Thursday, November 7, 2013

Keeping Warm

Spending a warm summer night under the stars can be one of the most enjoyable, relaxing experiences around for anyone, serious astronomer or not. Unfortunately, the weather is not always conducive to comfortable astronomy, often the exact opposite in the case. As any astronomer who has gone through a full year of observing can say, there's nothing colder than a clear winter night. Herein arises the question: how to keep warm?


The bad part about astronomy is that it is a stationary hobby so, without any movement to build up body heat, you can get cold really quick. As a general rule, seasoned astronomers will always tell a newcomer to dress (or at least have handy) clothing that will suffice if it were actually 10 degrees colder than the forecast low for the night. Bottom line, if it's going to get down to 50 tonight, dress as though it were going to be 40. Another tip: layer up. When layering, your body heat will warm up the air between the layers of clothing, providing for some very effective insulation. As hard as it may be to believe, layering three lightweight coats can actually be as warm as (or warmer) than a single winter coat. Try it and see.


Light Pollution

Statistically, most people in the developed world live in cities/suburbs, which are not all that great settings for doing astronomy. In fact, living in such a location probably prevents a great number of people from taking up astronomy in the first place, which need not happen as there are ways to beat the light.
First of all, what does light pollution look like?


Have you ever gone outside on a cloudy night and noticed how light it was? The answer to this question, for anyone living in a city/suburb is going to be “a lot.” This effect can be greatly magnified when there is a snowstorm overnight, too. Naturally, none of this light is natural. In its purest form, a cloudy night should be dark, not have a reddish hue to it. Needless to say, this is a very practical example of light pollution, or stray light beamed away from the ground that serves no other purpose than to brighten up the sky.


Now, this is not to say all light pollution is this bad, as there can be greatly varying levels that can present themselves in different ways.


In 2001, John Bortle devised a scale for determining light pollution. The scale runs from one to nine, with higher numbers indicating more light pollution. Here is a breakdown of the scale, magnitudes listed are for people with exceptionally good vision.

Level 1: Excellent dark sky site, stars as dim as magnitude +8. The brightest areas of the Milky Way cast very visible shadows. Bright planets, Venus, Jupiter, Mars at a close approach, all seem to inhibit proper night vision. This is an observers dream.

Level 2: Typical dark sky sight, stars to magnitude +7.5. The Summer Milky Way is structured to the naked eye, the Zodiacal Light is still bright enough to cast shadows. Many globular clusters are naked eye objects.

Level 3: Rural sky, stars to magnitude +7. Only a hint of light pollution near the horizon, where clouds may appear slightly illuminated. Clouds dark overhead, appear as a starless black void in the sky. Zodiacal Light rises over 60 degrees when standing straight up. Any telescopes are apparent only to about 30 feet.

Level 4: Rural/suburban transition, stars to magnitude +6.5. Light pollution domes over cities are apparent, clouds are illuminated in brighter areas of sky, but still dark overhead. Zodiacal Light extends about 45 degrees up at best. Milky Way still easily visible, but most detail is now gone.

Level 5: Suburban, magnitudes to +5.9. Only hints of Zodiacal Light visible on best nights. Milky Way only a faint haze near zenith and washed out near horizon. Light sources very apparent, any clouds are brighter than the sky.

Level 6: Bright suburban sky, magnitudes to +5.5. Zodiacal Light now invisible and only a hint of the Milky Way is seen near the zenith. Clouds are fairly bright. You will have no trouble seeing eyepieces on a table at a distance. The third of sky nearest to horizon glows a grayish-white color.

Level 7: Suburban/urban transition, magnitudes to +5. Entire sky has a grayish-white hue to it. Milky Way now invisible, clouds appear as glowing.

Level 8: City sky, to magnitude +4.5 at best. Sky begins to take on an orange glow, you can read newspaper headlines easily. Constellations incomplete as dim stars are now invisible.

Level 9: Inner city sky, magnitudes of +4 or less. Sky is lit to zenith, All but the brightest constellations appear incomplete, dim constellations are invisible.
Not only where you observe from can impact what you see, but the characteristics of the air itself can play a huge role. Humid air is an observer’s second worst enemy, only behind light pollution. For visual observers, all of the tiny water droplets in the air reflect light, thus magnifying any already existing light pollution. The drier the air, the better the observing. On the most humid of Summer nights in suburbia, third magnitude stars can be a challenge. However, a few days later on a dry night, the Milky Way might be visible from Zenith down to about 45 degrees. This vast difference in what is visible can be due to humidity alone. 


Now, light pollution understood, how to beat it?



The easiest way (other than driving out into the country) is to simply go to the backyard. Think about it: do people put lights behind their houses? Without all of the walk lights on the fronts of houses, the backyard is a lot darker than the front. In addition, houses are great blockers from street lights, too. So, without all of this artificial lighting, it's an easy claim that you can drop one level of John Bortle's scale just by changing your observation location without leaving one's own property. 

 
For someone really dedicated and who has a little money to burn, it might be a good idea to build a small, privacy fence-enclosed area in one' s backyard. By doing this, one can block out even more light. By doing so, one can block out all the stray light coming in from the sides, preserving night vision by allowing only a straight up view of the night sky. To add to a fenced in area's effectiveness, paint the inside of the walls flat black so prevent any reflectivity.


If you are really serious about your astronomy and have a lot of money to spend, it may be a good idea to invest in a small observatory. As funny as it may seem to a beginner, many companies sell ready-to-build observatory kits. By building an observatory, one can block out even more light than with a privacy fence and, in addition, have an outdoor storage space for all of one's astro toys. 

Night Vision

Humans are not designed to be nocturnal; therefore the human eye is not as well suited to nighttime viewing as a night animal, say a cat’s. The reason for this inability to see as well at night as a cat is that the pupil of the human eye does not open nearly as wide as a cat's. The pupil is what controls the amount of light allowed into the eye. Naturally, for seeing in the dark, the ability to let in as much light possible is important. If you look at a cat in a relatively dark setting, you will see that the iris, the colored part, of the cat’s eye is almost completely blocked out by the black pupil. This is because the pupil is almost completely open, which lets in the most light possible, which translates to excellent night vision. In bright sunlight, a cat's pupil appears as a tiny black slit in the middle of the colored iris. Unfortunately, for naked eye astronomers, the human pupil can not open up to the amount that a cat’s can. The good news is that the human pupil can open up to a certain degree, the bad news is that this process takes about ten to fifteen minutes. So, before stargazing, give your eyes at least ten minutes to adjust to the dark. Once you get used to looking at the stars, you will notice a difference. Many more stars will be visible after ten minutes than after just after stepping out of your probably well-lit house, human night vision at work.



Once optimum night vision has been achieved over the course of about ten minutes, a split second can ruin it. Since the human eye is more adept at picking up light than seeing in the dark, the pupil quickly dilates, or closes at the sight of a bright light. Once dilated by a bright light, it will take time to re-achieve night vision, with time being directly dependent on the intensity and color of the light, which is also an important consideration. 


The spectrum of visible light runs from red, orange, yellow, greed, blue, indigo, and violet (thing 'Roy G. Biv'). Colors on the red end of the spectrum have longer wavelengths and less powerful frequencies than the short wavelength light on the violet end of the spectrum. Since the power of the wavelength can vary with color, it should come as no surprise that reddish colors with longer wavelengths at lower frequencies are less damaging to night vision than other colors. This lesson on the color spectrum explains why you will only see red shaded flashlights at any gathering of observational astronomers. 


Getting back to night vision, it is a good idea to go behind your house if you live in a suburban setting to avoid all of the car headlights going up and down the street, with each pass re-ruining your night vision. In addition to escaping from headlights, escaping street and house lights can do wonders for the amount of stars you will be able to see.

Eyepieces

While many people are all about the telescope, the eyepiece often comes as an afterthought. For a serious astronomer, this can be somewhat of a mystery as the eyepiece can go a long way in making viewing more enjoyable or, at the least, more varied. 


The first question many people have with eyepieces is 'how powerful is it?' Well, there is no single answer to that question as eyepiece power is directly related to what telescope it is being used with. To find eyepiece power, simply divide the telescope's focal length by the eyepiece's focal length. Example: a 10mm eyepiece in 1000mm scope (1000 divided by 10) results in 100x power. In a 500mm scope, that same 10mm eyepiece results in 50x power (500 divided by 10). 


Another thing to consider about eyepieces is the size of the opening through which you look. Old-fashioned eyepieces resemble peepholes when of short (powerful) focal lengths. Now, thanks to computer design and ever-increasing creativity, some short focal length eyepieces can have massive openings, providing bay window-like views to the universe.


A final consideration of eyepieces is their angular field of view. Needless to say, the wider the field, the better. Unfortunately, for those super-wide, 90+ degree fields, you'll be paying a lot of money and using eyepieces that seem to weigh as much as bricks.


Lastly, good eyepieces come in two sizes: 1.25 and 2 inch diameters. The small, .965 eyepieces bundled with some department store telescopes are a sure sign of a junk telescope as no modern company with any degree of self-respect would market such a product.

Mounts

For many beginning astronomers, the mount the telescope sits on is often, erroneously, an afterthought. Bottom line: the mount can make or break the observing experience whether it be through merely being too small or simply not having the desired functionality. Telescope mounts fall into three main categories, each of which will be examined.


Equatorial. The equatorial mount, while being initially difficult to use for a beginner, is the type of mount prized by the most serious of astronomers. Operating on a dual axis design, the equatorial mount can, when equipped with a motor drive, track the stars as they move across the sky during the course of a night. For this reason alone, it is the choice of the serious observer and the only choice for any astrophotographer more advanced than tripod photography. Another plus of the equatorial mount is that it will come equipped with slow motion controls, which allow for manual adjustment of the telescope in the most minute motions to compensate for Earth's rotation without the use of a motor drive. The only real down side of this mount design is that it can be just about impossible to point the telescope close to the North Celestial Pole.


Alt-Az. An abbreviation for “altitude-azimuth,” the alt-az. mount is a simple point and look affair. For the beginner, this is perhaps the most user-friendly mount on the market as it is, without doubt, the most intuitive in use, simply grab, aim, and look. For serious observers who want a second, often portable mount, a small mount of this design is often the preferred choice. Like the equatorial, the alt-az can come equipped with slow motion controls. Unfortunately, unlike on an equatorial where hand-controlled tracking can be done by turning one knob if polar alignment is true, no such thing can be done on an alt-az as you'll find yourself working both knobs simultaneously for the simple reason that the mount can't align with your latitude. Also, look out for your tripod legs when aiming.


Dobsonian. The simplest of all telescope mounts, the Dobsonian is essentially an alt-az using a lazy susan rather than a tripod and mount head design. First popularized by John Dobson in the 1980s, the Dobsonian has become the mount choice for large reflectors in recent years thanks to its simple design, low cost, and the fact that it sits low to the ground, thus eliminating the need for step stools to get to the eyepiece. On the down side, the Dobsonian has no slow motion controls and can be quite a pain to aim when trying to view near zenith. Still, just by looking how most reflector rigs are sold today will leave no doubt in one's mind that the Dobsonian is immensely popular.


Telescopes

There are three main telescope designs, refractor (lens-based), reflector (mirror-based), and compound (both lenses and mirrors). Each scope has benefits and drawbacks depending on what you will be observing and where you will be observing from.


1. Refractors. A refracting telescope is the oldest telescope design. The first refracting telescopes were spyglasses intended for terrestrial purposes that were turned skyward. Galileo’s pioneering discoveries were all made with a very basic refracting telescope. A refracting telescope uses a lens to gather the light. The lens is shaped so that the light is bent (refracted) down to a focus point. After the focus point, the image is flipped and continues a short distance before hitting a diagonal mirror which then flips the image back to right side up and directs it into the eyepiece at the same time. Because of this, refracting telescopes can also be used for terrestrial pursuits, such as bird watching. This is the basic anatomy of a refractor. Although two refractor designs will be dealt with, the difference in the two types is in the glass used, not the design.


Achromatic refractor. Achromatic refractors are refracting telescopes with a lens made of two individual pieces of glass. Commercially made achromatic refractors usually range from 2 to 6 inches in aperture. The focal ratio usually ranges from f/5 to f/12. While these are the most common standards, achromatic refractors can go over 6 inches in aperture or over f/12 in focal length. It is virtually unheard of for a refractor to be less than an f/5 length. Achromatic refractors provide unrivaled image sharpness because of a clear aperture and color contrast, which is created by using a lens. An achromatic refractor will easily out perform larger scopes of other designs in the area of contrast and sharpness. While usually marketed for planet and double star observing, achromats of about 3.5 inches or larger are really excellent all around telescopes, except in the faint galaxy department where more aperture is needed. Because of the high color contrast, refractors are by far the best type of telescope to use in light polluted settings because the object being observed stands out well in contrast to the dark background.

There are two major drawbacks with an achromatic refractor. First, the eyepiece is at the base of the tube, which means that the eyepiece can be quite low when observing objects high in the sky. However, the height problem can be fixed with mount extensions to raise the scope.

The second problem is chromatic aberration. Because the objective is made of standard glass, it is difficult to bring light to a single focus point at focal ratios under about f/12. The colors of the spectrum have different wavelengths, red having the longest and violet the shortest wavelength. The goal of the lens is to bring these colors together at a single point to create an image. However, the glass used in achromatic refractors can not accomplish this task completely unless the lens is a long focal length. Because of their shorter wavelength, colors on the violet end of the spectrum are not brought to focus with the rest of the colors. The result is a purple halo around bright objects, especially noticeable at higher powers. Views of chromatic aberration vary. While some people easily ignore it, other observers are driven crazy by the false color. Long achromats, about f/15 or longer, can virtually eliminate chromatic aberration on all but the brightest objects, but the length can be a problem, especially for larger aperture scopes.


Apochromatic/ED refractors. Apochromatic/ED (Extra Low Dispersion) are interchangeable names for refractors that retain all the high contrast and crystal clear sharpness of an achromat while eliminating the chromatic aberration. Without a doubt, apo refractors provide the best images per inch of aperture of any telescope design. The key to the apo refractor is in the glass. Apo refractors use anywhere from a two or sometimes even a five element lens design. With extra layers of high quality ED glass and strategic spacing in between, an apo refractor can bring all the colors of the spectrum to a single focus, eliminating any false color. Apo refractors are usually at least 2.5 inches in aperture and some companies even offer apos over a foot in diameter. The focal length is, like the achromat, at least f/5. Large apo refractors are an astrophotographer’s dream scope. For photography through a telescope, nothing can beat the combination of pinpoint sharpness, high contrast, and lack of false color that only an apo refractor can provide. Like other refractors, an apo can be raised with a mount extension to bring the scope up to a more reasonable height. With all of these features going for them, apo refractors are probably the closest thing to the perfect telescope. However, with apo refractors, there is a downfall. For all of these perks, any would-be apo owner will have to pay a premium price. A 3 inch apo optical tube with no accessories selling for $500 is a bargain. A fully outfitted 4.5 inch achromat with a tripod and accessories can be bought for about the same price. But if money is not an object, an apo refractor is probably the best way to go.


Summary. Refractors, of all the telescope designs, are the most expensive per inch of aperture. But if you have the cash, a refractor is well worth the extra investment. Refractors offer unrivaled image clarity, making them the obvious choice for anyone who likes to observe planets and/or double stars. The internal baffling of the tube can greatly reduce internal glare, boosting the color contrast of your targets. The high color contrast of a refractor lends itself nicely to light polluted areas. Another perk of a refractor is the greater light transmission. Refractors average at least 90% light transmission, with some premium refractors being tested at as much as 98% light transmission. On the other hand, the best reflectors only transmit about 75% of the light collected to your eye. Because of the high contrast and greater light transmission, a refractor can outperform larger scopes of other designs for even deep sky objects, especially from cities and suburbs. Another perk of a refractors are their size, which makes them easily portable. Achromatic refractors, especially those over 4 inches, are great all around performers and the economical refractor choice for a beginner. Another big advantage: a closed-tube design, which means no internal dust, and the fact that it is virtually impossible to knock a main lens out of alignment without trying.




Reflectors. Physics pioneer Sir Isaac Newton, bothered by the lack of high quality refractors on the market at the time, built the first reflecting telescope around 1668 (exact dates can vary). Reflecting telescopes use a set of mirrors to gather light. The primary mirror for a reflector is housed in the rear of the tube. The light enters the tube, bounces off of the main mirror toward a small secondary mirror, which then directs the image up through the eyepiece. Unlike refractors, the image in reflectors stays upside down.


The modern reflector is essentially unchanged in design from the first one built by Newton and has the mirror arrangement as described above. Commercially built Newtonian reflectors can range anywhere from about 4 ½ inches to three feet, yes three feet, in diameter. The focal ratio of a reflector is typically an f/4 to f/8 range. Because of their smaller aperture, small aperture reflectors are typically longer in focal length. Because of their large diameter, large reflectors are usually at the short end of the length spectrum. An example of this fact is the following comparison. A six inch, f/8 reflector is a common design at about 48 inches long. A ten inch, f/4.5 is another common design, about 45 inches long. A long focal ratio, large aperture reflector would just be too difficult to handle. Not many people would want to mess with a ten inch, f/8 reflector about 80 inches long. The focal ratio determines what the telescope is best suited for. Long 6 inch, f/8 reflectors are good all around performers, but are somewhat limited to a narrow field of view because of the long focal length. An f/4.5, ten inch reflector is best suited to deep sky observing because of its large aperture and short focal length, which allows for a generous field of view. Probably a good, middle of the road choice is an eight inch, f/6. 

Advantages of the reflector include the mirror light collection system itself. With a mirror, chromatic aberration is not an issue. Also, a mirror located at the rear of the tube is less prone to collecting dew than a lens at the front of a refractor or compound design. The reason many beginners go for reflectors is the cost. A Newtonian reflector is the cheapest design per inch of aperture of all telescopes. However, there are drawbacks to a reflector.

One drawback is due to the mirror system. The pair of mirrors must be kept in line. Collimating, is the process of aligning mirrors and this will undoubtedly have to be done sooner or later. When it comes to handling, Newts are the most fragile of telescopes. Another drawback of the mirror is that the reflective coating will need to be replaced with enough time. Bulkiness is an issue for some people. Many reflectors are typically about four feet long with apertures of up to a foot. This may prove too large for some people to want to carry outside very often. For many astronomers, by far the biggest complaint about Newtonian reflectors is the secondary mirror. The small secondary mirror is supported by a four pronged “spider” at the front of the tube. The “legs” lead to diffraction spikes appearing on stars. While to some people, the spiking is aesthetically appealing, it is an annoyance to others. Even for people who think the spiking just adds to the beauty of the stars, the secondary mirror obstructing the tube definitely degrades the image sharpness/contrast. Because of the obstruction caused by the secondary mirror, no reflector will ever match a refractor in the clarity and resolving department. However, the clarity and resolving ability of a reflector is not bad at all, it just is not quite as good as a refractor. Also, while refractors are greatly limited in size because a lens is only supported on its periphery, a mirror can be supported underneath, allowing for giant telescopes. Some companies offer ready built reflectors of up to three feet in aperture.


Summary. The simple Newtonian reflector is by far the cheapest telescope design around. Because of the cost, a six to eight inch reflector is often considered an ideal choice for a beginning astronomer. Reflectors offer some decided advantages over other designs. First is the low cost. Reflectors are also the least likely design to be effected by dew formation. Another benefit of the mirror is the lack of false color. The older Newtonian design offers these benefits but has some disadvantages. Mirrors will occasionally have to be realigned and refinished. Diffraction spikes provide varying reactions. But the undeniable drawback is the clarity. While Newtonians can split double stars and resolve detail in the cloud bands of Jupiter, a refractor will always be better for clarity and contrast. The new clear aperture reflector design offers great potential. With the lack of false color and clarity, apo refractors may soon be challenged as the best telescope design around.




Compound. The compound design is a relatively recent idea that uses a system of mirrors and lenses to produce an image. The light enters the telescope through either a front plate or corrector lens. From there, the light travels to the rear of the tube to the primary mirror. After reflecting off of the primary mirror, the light travels forward to a small secondary mirror attached either to the corrector lens or front plate, depending on the design. From the secondary mirror, the light is directed back toward and through a hole cut in the primary mirror, finally reaching the eyepiece. Because of the back and forth reflecting, a compound design telescope tube is much shorter than either a reflector or refractor, despite being of often longer focal lengths. The two most common designs here are very similar visually to a beginner, the differences in the fine details.


Maksutov (Maks) use a spherical, meniscus shaped corrector lens in the front of the telescope. This corrector lens is the distinguishing feature of a Maksutov design. Maks are of often a longer focal ration than the Schmidt design (mentioned later). The longer focal length results in a less steeply curved primary mirror, which means less need for image correction. For the secondary mirror, Maks use an aluminized section on the back of the corrector lens. This is easier than mounting an actual mirror but by using the back side of the corrector as a secondary virtually fixes the focal ratio of a Mak, usually at f/15. Although the field of view of a Mak is quite small, the small secondary ups the contrast compared to a Schmidt. Also, because of the use of a glass corrector lens in the front, Maks are usually limited to about six inches. Any greater aperture would be too front heavy because of the large lens.


Schmidt. The Schmidt design uses an aspherical corrector plate as the front objective with a secondary mirror mounted on the back of the plate. The corrector plate of a Schmidt is more complex that the corrector lens of a Mak. The Schmidt corrector plate appears flat, but is actually thicker in the middle and around the edge. Unlike the Mak, the Schmidt design uses a real mirror mounted on the back of the corrector plate. Unfortunately, the secondary obstruction of the Schmidt is the largest percentage of any telescope design, which degrades image sharpness. The good news about the Schmidt is that it is shorter, typically f/10, allowing for a wider field of view than the Mak. Because of this, Schmidts are better for deep sky viewing. Because of the lighter corrector plate, Schmidts can be built bigger, up to two feet for commercially built models.

As with everything else, though, there are disadvantages. Like Newts, compound designs are obstructed by a secondary mirror, which will degrade image clarity/sharpness somewhat. Like refractors, with front-mounted optics, these scopes are also more prone to dewing up, especially considering that, unlike refractors, they are often sold without dew shields! AS for the biggest problem of the compound design it all has to do with the focusing. Unlike refractors and Newts, which are focused by racking the focuser in and out, this changing the length of the scope, the compounds are focused by moving not the eyepiece, but the main mirror, which creates two problems. First, and most common, mirror flop. Swinging a compound scope around the sky can actually defocus the scope because the main mirror will slide around, albeit slightly. Second, because the tube is not sealed, moisture can actually get inside the scope, resulting in inner dew and, if the scope in not allowed to dry, fungus.


Summary. When it comes to portability, nothing beats a compound design. Models under six inches are an ideal scope for any astronomer who likes to travel. The great advantages of the compound design revolves around the short tube design. With the short tube, looking into the eyepiece will never feel like a stretching exercise. Large scopes are still compact for their aperture and are a common choice for anyone considering building an observatory with a permanently mounted telescope. Like the reflector, chromatic aberration is never an issue. Maksutovs have small fields of view but provide clearer, higher contrast images because of the smaller secondary mirror. Schmidts are shorter and can be built bigger, but at the price of having a substantially larger secondary mirror than the Mak. Either way, size wise, nothing beats a compound design.





What is best?
The question of what is the best telescope has no right or wrong answer. What constitutes an ideal scope is determined by where the scope will be used and the preferences of the observer. In only a few situations can any actual recommendation be given with confidence. If you live in a light polluted city where only planets and bright stars are visible, a small refractor is the way to go, unless you know of a dark site you can go to in the country. Even a 60mm refractor at high power can be used to successfully reveal the cloud bands of Jupiter, the rings of Saturn, and split many double stars. From a bright city setting, trying to find deep sky objects will be a futile search, making a large aperture, deep sky scope useless for its intended purpose. For observers living under dark skies where the Milky Way is easily visible, aperture should be the goal. Because deep sky objects will be easily seen, the largest telescope that can be easily taken outside would be the ideal scope. Just be careful not to go too big. A scope too big to transport easily will probably hardly ever get used. A small compound, under 6 inches, is ideal for anyone who likes to take their hobby out on the road. Some small scopes can be made to fit a lightweight camera tripod, which are perfect for traveling astronomers. For anywhere in between, and recommendations are hard to give. A great piece of advice for someone buying a telescope is to go to a star party and look through as many types of telescopes as possible. The best way to discover your personal preferences is to look, reading descriptions can only go so far. According to many astronomers, the best telescope is one that will be used and not left to sit and collect dust in a closet.


Spotting Scopes

Spotting scopes, intended for nature watching, are also great for beginners when turned skyward. Spotting scopes are small telescopes of either refractor or compound design. The reason that you will never see a reflecting spotting scope is that reflectors always produce upside down images.


While spotting scopes are more expensive than binoculars, they do offer some advantages. Some spotting scopes come with a tripod and even if it doesn’t come with a tripod, all spotting scopes can be made to attach to tripods to provide a stable viewing platform. Another great benefit of spotting scopes is that many have adjustable magnifications that usually range from 20x up to 60x. The adjustable magnification is great for finding objects and then zooming in on them. The only downfall is that even at low power, 20x, the field of view will be quite small. At 60x, you have the equivalent of low power for an astronomical telescope. Some spotting scopes even come with eyepieces like an astronomical telescope. Some spotting scope eyepieces can also be used on an astronomical telescope when you decide to upgrade.


As with binoculars, spotting scopes can have their viewing field expressed in degrees or feet at a particular distance. Use the same method as for binoculars to calculate the field if it is expressed in feet. Again, higher magnification reduces the field of view.


Like binoculars, aperture is important. The larger the aperture, the better.


Binoculars


Binoculars are essentially two small refracting telescopes put together and are very cheap, but can be great for looking at the stars, especially when coupled with a tripod to eliminate the shaking that we all have some degree of in our hands. With the shaking eliminated, dimmer objects can be resolved.

When it comes to buying binoculars, they can be picked up at most department and sporting goods stores for under $50. For beginners, any binoculars will do, as long as they met a few basic specifications that are suited to astronomy.

Binoculars are sized by two numbers, 10x50, for example. The 10 refers to the magnification power and the 50 refers to the lens aperture. For astronomy, a pair of binoculars with a magnification of ten or twelve is ideal. Anything less that ten is often underpowered for viewing some brighter deep sky objects, especially if light pollution is an issue. Anything much greater than twelve often is a problem because of two factors. First, at higher magnifications, shaking in your hands can really become a problem. Second, the higher the power, the smaller the field of view. Even for experienced astronomers, a generous field of view is desired to eliminate any need to search, which is better spent looking at the sky. With binoculars, searching should not consume much time.

The second number, the aperture, is also important. Anything less than 50mm won’t let enough light in, which will limit what you can see. In astronomy, aperture is everything. For aperture, higher is always better. If you find two pairs of binoculars for close to the same price, say a 10x50 and a 10x70, go for the one with the larger aperture. With a larger lens, more light is let in and objects will look brighter.

Another important consideration for astronomy binoculars is field of view. For most people, anything less than a 5 degree field will be too small thanks to both the narrow field making things harder to find and for being more prone to hand shake. Personally, anything with a 5-7 degree field is the happy medium. Generally speaking, binoculars with 7-10x power fall into these fields of view.

Sunday, November 3, 2013

The Sky's Motion

Like the Sun, the stars move in the night sky. For proof of this, go out on any clear night and look up, noting the positions of a few bright stars, then go back inside for a few hours. Later in the night, go out again and, guess what, the stars have shifted position.

So, how does this work?

The most important thing to understand is that the sky itself does not move, the Earth moves and the motion of the sky is only apparent. So in technical terms, referring to “sunrise” or “sunset” is incorrect as the Sun doesn't move. The motion of the Sun, and other stars, is caused by the rotation of the Earth. The Sun and Stars are all at fixed points in space and the Earth is not. For an easy comparison, stand in a room and twirl around. By doing this, you are simulating the relationship of Earth to the stars. You are the rotating Earth and everything in the room is a star. Objects in the room appear to move even though you know they are stationary, only you are actually moving. The situation is the same for the Earth and stars. Ironically, despite knowing this fact for hundreds of years, we still have yet to adopt it into our daily language.

If you go outside and observe the location of the Northern stars over the course of a night, you will notice that they revolve around a single point in the sky. The question quickly becomes “why?” The answer is simple. The Earth is surrounded by stars in all directions. Imagining a giant arrow starting at the Earth's South Pole, extending through the core of the planet, to the North Pole, and out into space. The North Celestial Pole lies directly overhead of the Earth where the head of the arrow is pointing. In a modification of the experiment in the above paragraph, twirl yourself around in a room looking straight up at a fixed point on the ceiling. The point you are looking at will remain stationary and everything else you see will seem to revolve around that fixed point. The same exact thing happens with the Earth. In fact, every star revolves around the Celestial Pole, but those stars that are far enough away from the pole, out of the circumpolar region of sky, appear to rise in the East and set in the West. Over the South Celestial Pole, the same thing happens as in the North.

Comets

The rarest of all celestial visitors visible to the naked eye, comets are capable of, by far, the most variety. When one hears the word 'comet,' the thought of a long-tailed object comes to mind. Yes, while comets can look like this, these 'great comets;' are exceedingly rare. To illustrate, the last great comet, McNaught, was visible in 2006-7. Before that, Hale-Bopp (1997) was the last great comet. While there was Hyakutake the year before in 1996, Halley's Comet's 1986 appearance was the last great comet before that. Just by looking at these examples, the pattern becomes obvious: great comets are, on average, a once a decade event.

Now, while not all comets are the pop culture image great comets present, they are fun to look at. With the naked eye, comets can be visible as diffuse fuzzball-like objects in the sky. In binoculars and telescopes, comets can take on a lot more detail, especially in regards to color. For comets, the most common color is a greenish blue, which can be extremely delightful to look at in the telescope as there are no green objects in the sky.


Another interesting point to comets is that they are unpredictable. While forecasters will make predictions about what any given comet will do months in advance of its arrival, comets often have other ideas. A prime example of this was Comet Holmes in 2007, which morphed from a small, normal binocular/telescopic comet just on the edge of naked eye visibility into a massive body as large as the full Moon. The same can be said of Comet McNaught. While bright, no one could have ever expected it to erupt a sky-spanning tail after making its close passage to the Sun. To say the least, comets are true cosmic wild cards that are always worth a look.  

The Moon

Of all heavenly bodies, the Moon is perhaps the most fun to observe with the naked eye thanks to the fact that it changes phases and because one can actually see surface features without optical aid.

When it comes to Moon's phases, they are actually very easy to explain. Although it may not always appear so to us, the Moon is always half lit. What we can see and when we can see it depends on where the Moon is in its orbit relative to the observer. To explain what is happening, let’s take a trip around the Earth by way of the Moon. A total orbit of the Moon around the Earth takes about 29 days. At new Moon, the alignment is Sun, Moon, and Earth in that order and in a straight line. From the Earth, the Moon is lost in the glare of the Sun, hence why we cannot see it. As the days progress, the Moon will move out of the Sun’s glare and the Sun will set before the Moon. In the days just after new Moon, from the Earth, we will begin to see a tiny bit of the lit side of the Moon just after sunset.

As the days progress, we will continue to see more of the lit side of the Moon as our cosmic companion distances itself from the Sun’s glare. As the Moon moves from new to first quarter, it is called a waxing crescent. At first quarter, the point in its orbit where the Moon has gone a quarter of the way around the Earth, the Sun, Earth, and Moon form a 90 degree angle, with Earth serving as the right angle of an imaginary cosmic triangle. Because of this 90 degree angle, the Moon appears half lit to us on Earth because we see exactly half of its lit side. At first quarter, the Moon also rises exactly half way between sunrise and sunset.

As the moon continues in its orbit from First Quarter, it is now farther from the Sun than the Earth. After the angle to the Moon relative to the Earth is over 90 degrees, we see more than half of the lit side of the Moon and the Moon continues to rise later each night. At this point of being over half full, the Moon is now called a waxing gibbous.

At full Moon, the Sun, Earth, and Moon are all in a straight line relative to each other. The Moon is now appears full as we can see the entire lit side because it is directly opposite the Sun in the sky. After full Moon, the Moon continues its orbit, now traveling back toward the sun as a waning gibbous. We see less and less of the lit side of the Moon as it returns toward the Sun. At third quarter, when the Moon reaches a 270 degree angle from the Sun, we again see half of the lit side and half of the dark side. The Moon now rises exactly between sunset and sunrise. After third quarter, the Moon now moves even closer to the Sun as a waning crescent, rising later each day until it is again lost in the glare of the Sun as a new Moon.

The Sun


First of all, this should go without saying, but NEVER look at the Sun without specialized eye protection, whether it be in the form of eclipse glasses or solar filters for binoculars/telescopes. For penny pinchers who do not want to use eclipse shades, a #14 or darker welder's shield will work when observing the Sun with the eye alone. When looking at the Sun with the naked eye, it will often appear as a single-colored disk save a few large, dark sunspots. When turning binoculars and even or powerful telescopes on the Sun, the spots will appear more detailed, with clear shapes becoming visible.

In telescopes, the real fun starts when moving out of visible light into very specific wavelengths. By doing this, one will be able to see granulation, which gives the Sun the appearance of boiling water, flares, which appear as giant flames erupting off the solar surface, and prominences, arches of fire that loop up and then down again. Unfortunately, all of this added detail comes at a cost, literally, as such filters/specially-built telescopes cost a lot more than standard, visible light filters.   

Planets

Only five planets, Mercury, Venus, Mars, Jupiter, and Saturn are visible to the naked eye. Under extremely dark skies, Uranus can be spotted but is indistinguishable from the stellar background and Neptune requires binoculars to even be seen at all. Many ways exist for classifying the planets. For observational purposes, only one classification really matters. For observers, the two types of planets are inferior planets within the Earth’s orbit and superior planets outside the Earth’s orbit. Where a planet is in relation to the Earth directly impacts its apparent motion throughout the sky. However, irregardless of where a planet is in relation to Earth's orbit, they all lie on the ecliptic plane, a narrow lane of sky wherein planets appear to travel and that represents the area where a disc of dust and debris existed at the formation of the solar system. In time and with the aid of gravity, this debris coalesced to form the planets.

Inferior Planets
Inferior planets are never seen to stray far from the solar glare and are only visible in the morning or evening. For planets within the Earth’s orbit, knowing some terminology is necessary. Greatest elongation, Eastern or Western, is the best time for observing the inferior planets. Greatest elongation refers to the time in a planet’s orbit where the planet is at its greatest angular distance from the Sun and at its highest in the sky as seen from Earth. Eastern elongation is when the planet is farthest East of the sun and this means the planet is visible in the evening and Western elongation means the planet is visible in the morning when it is farthest West of the sun. The worst time for observing an inferior Earth planet is during conjunction. For planets within the Earth’s orbit, there are superior and inferior conjunctions. A superior conjunction is when the planet being observed is on the far side of the Sun in a straight planet, Sun, Earth alignment. Inferior conjunctions occur when the planet comes between the Earth and Sun in a straight Sun, planet, Earth alignment. Either way, any conjunction is the time when a planet disappears into the sun’s glare.

Mercury.
Of all the planets, Mercury is the one most people never see. The great astronomer Nicholas Copernicus, who finally rediscovered the idea that the sun is the center of the solar system, reportedly never saw Mercury. The reason that Mercury is so difficult to spot is that it is so close to the Sun. The greatest possible elongation only takes Mercury about 28 degrees away from the sun. Because the ecliptic is rarely vertical, Mercury at greatest elongation actually appears much lower that 28 degrees in the sky most of the time. Because Mercury is an inferior planet, it is only seen in the early morning just before sunrise and early evening just after sunset. Mercury is best seen in spring evenings and on fall mornings when the ecliptic is nearly vertical, allowing Mercury to appear highest in the sky. When seen, Mercury averages out to be about a zero magnitude object near the horizon. Even though it is bright, because it is so close to the Sun, Mercury is often difficult to spot. Binoculars cure this problem. Because the sky needs to dim before the planet can be seen, any time that Mercury appears about ten degrees above the horizon is considered a good appearance. If you see Mercury, you will join an exclusive club of people who have seen the planet nearest to the Sun.

When looking an Mercury with binoculars, it still looks like a bright star without any special features.

 In the higher power of telescopes, Mercury appears to go through a complete set of phases from new to full and back again, just like the Moon. While interesting to watch in the present, in the past, the phases of Mercury (and Venus) conformed the theory that the planets do go around the Sun, not vice versa.
Venus
As the third brightest object in the solar system, only out-shown by the Sun and Moon, Venus is a true sight to behold. Venus is the second planet from the Sun and, because it lies within Earth's orbit, is classified as inferior. Because of its location relative to Earth, Venus can only be seen in the morning or evening. Averaging out at about magnitude -4, Venus cannot be missed. The greatest elongation possible for Venus is about 47 degrees. The best times for viewing Venus are Spring evenings and Fall mornings, when Venus can be seen about half way up to the zenith during a good appearance. At other times of year when the ecliptic is at a flatter angle, Venus appears much closer to the horizon. Because of its brightness and movement in relation to the Sun, Venus was given special significance by many ancient cultures, especially the Maya of Central America, who considered Venus just as important as the Sun. Because of its brightness, Venus is very easy to spot. So go outside when Venus is at its best placement, you can’t miss it.

When looking at Venus through binoculars, it may be possible to see phases if the binoculars are strong enough (above 15x power) and are mounted on a tripod.

In telescopes, Venus can appear to be a mini Moon because of its very obvious phases. Because it is closer to us then Mercury, when watching the phases of Venus, look for changes in the planet's angular size as the planet will appear at its largest as a crescent and its smallest as it nears full.
Superior Planets
Planets outside the Earth’s orbit exhibit different patterns of behavior. Depending on the location of the planet in its orbit, planets outside the Earth’s orbit can be observed at any time of the night and can be seen to traverse the sky, rising and setting with the stars. Here, a new term, opposition, enters the equation. Opposition is the time when a planet is 180 degrees away, directly opposite the Sun in the sky. This means that when a planet is at opposition, the planet rises as the Sun sets and sets as the Sun rises. At and around opposition, a planet is observable just about all night. Looking down on the solar system from above, opposition is a straight line of Sun, Earth, and planet. For outer planets, there is only one type of conjunction when the planet goes behind the Sun in relation to Earth, the superior conjunction of an inferior planet. And like the inner planets, outer planets are un-observable at and near conjunction. Another interesting phenomena takes place with the superior planets is retrograde motion, which is caused when the Earth passes a slower planet. A similar comparison is when you are driving on a highway and pass a slower car, which appears to fall behind you because it is being passed by your faster-moving car. A third bonus of the superior planets is that, along the ecliptic, lie some magnificent star clusters which the planets can appear to pass near or actually through. 

Mars
Of all the planets, Mars is often considered the most fun to visually observe. Because it is a superior planet, Mars retrogrades. But the real bonus with Mars comes about because of its highly elliptical orbit. While all planets change in brightness, most do only slightly. Mars is the notable exception. At its dimmest, Mars shines just shy of +2 magnitude. At its brightest, an obviously red Mars nearly reaches magnitude -3. Because of the highly elliptical orbit, the distance from Mars to Earth changes more than any other planet. The changes in distance bring about the dramatic changes in brightness. Mars is also notable because detail of the planet, its red color, can be observed without a telescope. Of all the planets, Mars is the probably the most fun planet to observe today while it was probably the biggest anomaly for ancient astronomers to explain. By observing Mars over the course of its 2-year orbit and various changes, it's no wonder that the ancients thought that it was alive.

In binoculars, Mars does not appear any different than it does to the naked eye, just a bigger, and more red.

 In telescopes, though, Mars can be a real treat. By using a medium-sized (4” and up) scope at around 200x power or greater, surface detail of Mars can become apparent, especially when Mars makes a close approach to Earth. The first things to look for on Mars are its polar ice caps, not unlike those of Earth, which can actually build and recede according to the Martian seasons. If you have a really big scope and really steady skies, more can be seen on the Martian surface, namely Mariner Valley, a canyon that would stretch from New York to Los Angeles if transported to Earth. Under the best conditions, one can observe differing colors on the Martian surface, which can, from time to time, be obscured my massive sand storms, whose existence is evidenced by temporary changes to the Martian surface coloring. In years past, it was thought that such changes in surface color were caused by the blooming and dying of of vegetation, much like that of deciduous trees here on Earth


Jupiter
Jupiter is the largest planet in the solar system and, because of its great distance, shines at a relatively constant -2.5 magnitude. Because of its twelve year orbit, Jupiter takes spends about a year in each zodiac constellation before moving on to the next. To the naked eye, Jupiter appears only as a bright star.

With optical aid, the game changes dramatically. In binoculars, while the cloud bands will still be invisible, one should be able to see the 'Galilean Moons,' named after their discoverer, the Italian astronomer Galileo. These four largest moons of Jupiter are named Io, Europa, Ganymede, and Callisto and are in that same order, with Io being closest to Jupiter and Callisto farthest. A simple way to remember them is to say 'I(Io) Eat(Europa) Green(Ganymede) Caterpillars(Callisto).' Okay, it's a little juvenile, but it works. For historical implications, the discovery of Jupiter's moons proved that not all objects went around the Sun, which was preached as gospel by science and Church until that time. Also, in binoculars, Jupiter transforms from looking like a bright star into a very obvious planetary disc. To see this, just look at the edges of the planet, which appear as a crisp line and not a diffuse glow.

In telescopes, Jupiter transforms from a featureless disc into a world alive with color. In even small telescopes, one can see distinct, reddish-pink cloud bands on the planet. The higher the power, the more detail one can resolve. In large scopes under steady skies, expect to see, with relative ease, swirling in the clouds along with the Great Red Spot. Another cool feature to be seen in a telescope at high power is the shadows of the Galilean Moons transiting the disc of the planet itself. Though not overly rare, these are fun events to observe, especially for a beginning astronomer.



Saturn
The last planet known to the ancients and the second largest planet, Saturn appears to the naked eye as a star shining around magnitude -.5. Saturn takes about 30 years to orbit the Sun and thus spends just over two years in any given constellation of the zodiac. Like Jupiter, Saturn shines at a relatively constant brightness thanks to its immense distance from Earth.

In high-powered binoculars on a tripod, Saturn's famous rings, while not being truly resolved, do present themselves in that the planet seems to have an oval shape to it, which Galileo termed as “ears.”.

Like Jupiter, even the smallest telescopes transform Saturn from a featureless disc into a wonderful world that must be seen to be believed. First of all, there are the famous rings, which appear easily at around 50x power. With larger scopes and higher powers, one can see gaps in the rings, most famously the Cassini Division. With very large scopes under steady skies, smaller divisions may also appear on a good night. Another thing to look for with Saturn are color bands, which are far more subtle than on Jupiter. With Saturn's rings, there is an interesting phenomenon that takes years to present itself. Because of the angles of Earth and Saturn relative to each other, Saturn's rings appear to 'open' and 'close,' with, once every 15 years years, the rings becoming edge-on and disappearing from view altogether. This slow progression can be observed in even the smallest of telescopes. Back to the big scopes, look for Saturn's moons. While giant Titan is easy to see, it can be possible to spot some of the other, much smaller ones, too.        

Stars

Even before going out and taking your first serious look at the night sky, you undoubtedly know that some stars are brighter than others. In astronomical jargon, the brightness of a star is known as magnitude. The magnitude scale is unusual in that it works in both positive and negative numbers. On the scale of brightness, the lower the number, the brighter the object. 

There are two kinds of magnitudes, apparent and absolute. The absolute magnitude is the actual brightness of a star. Stellar distances greatly vary. Some small stars that give off a relatively small amount of light are close and appear bright while some giant stars are very far away but appear dim. A comparison can be made with light bulbs. A nightlight at five feet away will look brighter than a 100 watt bulb at 300 feet away. The same is true of the stars. But for observational purposes, the magnitude to be concerned is the apparent magnitude, which simply refers to how bright the star appears to be in the night sky. The Sun, undoubtedly the brightest object in the sky, blazes away at an apparent magnitude of -27 while, for most people, a magnitude of +5 to +6 is the naked eye limit on the dim side of the spectrum. Needless to say, a combination of good eyes and dark sky can produce the ability to see even dimmer stars.

The magnitude scale is not an arithmatic scale because stellar brightness does not increase or decrease by a factor of one. A difference of one stellar magnitude translates to about a 2.5 change in brightness. For example, a zero magnitude star is about 2.5 times brighter than a first magnitude star. To compare brightness of stars, just multiply 2.5 to the power of magnitude difference. For example, to find the magnitude difference between a third and zero magnitude star, multiply 2.5 x 2.5 x 2.5 (2.5 to the third power) for an answer of 15.6, which means that the zero magnitude star is about 16 times brighter than the third magnitude star.
After brightness, the next thing to look at with stars is their color, which is a direct giveaway to a star's temperature. When it comes to stellar classifications by color/temperature, there are 7 classes that matter to the visual astronomer: O, B, A, F, G, K, M. A common way to remember this is by the saying 'Oh(O), be(B) a(A) fine(F) girl/guy(G), kiss(K) me(M)!' For students, the saying 'Oh boy, an 'F' grade kills me!' will also work equally well. When it comes to what the classifications mean, here's what we get:

(Hottest, usually largest)
O: Blue, hottest stars
B: Blue-white
A: White
F: Yellow-white
G: Yellow (our Sun is a 'G' star)
K: Orange
M: Red (coolest stars we can see without optical aid)

(Coolest, usually smallest save red giants)

Generally speaking, most of the stars in the sky fall between the A and G classification. Want proof of this? Just go out and look up. Now, it should be said that the stars do not look like Christmas lights in the sky, the colors are far more subtle. Still, though, by looking around the night sky, one can see that, while not obvious, the stellar colors mentioned above are, without doubt, very present. Obviously, in a telescope, the colors become very apparent. 

The Sky's Motion

Like the Sun, the stars move in the night sky. For proof of this, go out on any clear night and look up, noting the positions of a few bright stars, then go back inside for a few hours. Later in the night, go out again and, guess what, the stars have shifted position.

So, how does this work?

 The most important thing to understand is that the sky itself does not move, the Earth moves and the motion of the sky is only apparent. So in technical terms, referring to “sunrise” or “sunset” is incorrect as the Sun doesn't move. The motion of the Sun, and other stars, is caused by the rotation of the Earth. The Sun and Stars are all at fixed points in space and the Earth is not. For an easy comparison, stand in a room and twirl around. By doing this, you are simulating the relationship of Earth to the stars. You are the rotating Earth and everything in the room is a star. Objects in the room appear to move even though you know they are stationary, only you are actually moving. The situation is the same for the Earth and stars. Ironically, despite knowing this fact for hundreds of years, we still have yet to adopt it into our daily language.

If you go outside and observe the location of the Northern stars over the course of a night, you will notice that they revolve around a single point in the sky. The question quickly becomes “why?” The answer is simple. The Earth is surrounded by stars in all directions. Imagining a giant arrow starting at the Earth's South Pole, extending through the core of the planet, to the North Pole, and out into space. The North Celestial Pole lies directly overhead of the Earth where the head of the arrow is pointing. In a modification of the experiment in the above paragraph, twirl yourself around in a room looking straight up at a fixed point on the ceiling. The point you are looking at will remain stationary and everything else you see will seem to revolve around that fixed point. The same exact thing happens with the Earth. In fact, every star revolves around the Celestial Pole, but those stars that are far enough away from the pole, out of the circumpolar region of sky, appear to rise in the East and set in the West. Over the South Celestial Pole, the same thing happens as in the North.