Monday, July 18, 2016

Tonight's Sky for July 18: Full Moon

Tonight, the Moon will reach its full phase, which means that, as seen from Earth, it is directly opposite the Sun in the sky as seen from Earth and is at the half way point in its current orbit.


As for lunar mechanics, the Moon is always half lit. The reason we don't always see it as such is thanks to orientation in relation to us. Right now, when the Moon is opposite the Sun and on the far side of Earth, we can see all of its lit side, which is why it appears to be “full.” In the coming nights, we will start to see less of the Moon as its lit side starts to turn away from us as seen from Earth and heads toward Third Quarter. 

Sunday, July 17, 2016

Tonight's Sky for July 17: Jupiter Sets 2 Hours After the Sun

Tonight, Jupiter, 5th planet from the Sun and largest in the solar system, will be setting just 2 hours after the Sun, meaning that time to catch Jupiter under a truly dark sky is now virtually over and seeing the planet itself requires a relatively good Western horizon. So, if you haven't bothered to take a look at Jupiter in awhile, don't wait around much longer.

Saturday, July 16, 2016

Tonight's Sky for July 16: Comet Shoemaker-Levy 9 Hits Jupiter (1994)

On this date in 1994, telescopes all over the world were trained on the planet Jupiter, which was about to experience the first in a week-long series of impacts caused by tidally torn Comet Shoemaker-Levy 9. Going into the event, about the only things that were known was that this would be the first impact event ever to be witnessed by scientists and that no one really knew what would happen when the comet 'impacted' the gassy planet.

What did happen was spectacular.

On July 16, 1994, the first in a series of more than 20 fragments hit the planetary king, creating a large fireball and leaving a dark black area of gasses at the impact site. In time, Jupiter would come to have a virtual necklace of impact sites in its Southern Hemisphere, which also went on to have serious impact here on Earth in that, for the first time, the threat of planetary collisions from large objects shooting through the solar system was taken seriously.  

Friday, July 15, 2016

Tonight's Sky for July 15: Moon Crowds Saturn, Shadows Mars


As a bit of an encore from yesterday, which Saw the Moon, Mars, and Saturn form a triangle, the Moon will still be near Mars but will be parked extremely close to Saturn tonight. So, if you were clouded out last night, here's your second chance to catch the Moon and a pair of planets. 

Thursday, July 14, 2016

Tonight's Sky for July 14: Moon, Mars, Saturn Triangle


Want to see Mars and Saturn but have no clue where to look? Well, tonight's your lucky night as both Mars and Saturn will be very near the Moon. In fact, the three bodies will form a triangle. To see the show, simply go out and find the Moon. That done, you'll notice two bright 'stars' near Luna. These 'stars' are, in fact, the planets. Which is which? Since Mars is near its closest to Earth, it should be noticeably red in color. As for the yellow-white one, that's Saturn.



Wednesday, July 13, 2016

Tonight's Sky for July 13: Moon at Apogee

Tonight, the Moon is about as small as it will ever get thanks to the fact that the Moon is at apogee, a point in its orbit that is farthest from Earth.


What many people may not realize is the fact that the Moon (and all other celestial bodies) do not orbit their parent bodies in circles, but ellipses, which are slightly elongated circles. Result: any given day of an orbital period, any orbiting body will be at a slightly different distance from its parent body. As for the Moon, this variance in orbit amounts to about 20,000 miles.

As for tonight, the Moon will be about as far from Earth as it is going to get. When it comes to practical implications, the difference will be hard to notice with the naked eye to all but an experienced observer but, in a telescope, the difference will be obvious

Monday, July 11, 2016

Tonight's Sky for July 11: First Quarter Moon Meets Spica

Today, the Moon, second brightest object in the sky, has reached the First Quarter phase, which means that it is exactly 90 degrees around its orbit of Earth and is one quarter finished with its current orbit.. 

As for lunar mechanics, the Moon is always half lit. The reason we don't always see it as such is thanks to orientation in relation to us. Right now, with the Moon at a 90 degree angle relative to the Earth-Sun line, we only see half of the lit side.

After today, we will see more of the Moon each night as its lit side turns more toward from us and heads toward Full in a week.


Additionally, bright blue Spica, alpha (brightest star) Virgo, is nearby, too. 

Sunday, July 10, 2016

Tonight's Sky for July 10: Venus at Perihelion

Today,Venus is as close as it will ever get to the Sun thanks to the fact that it is at perihelion, a point in its orbit that is closest to the Sun.

What many people may not realize is the fact that Venus (and all other celestial bodies) do not orbit their parent bodies in circles, but ellipses, which are slightly elongated circles. Result: any given day of an orbital period, any orbiting body will be at a slightly different distance from its parent body. As for the point of an orbit farthest from the Sun, it's called aphelion. Lastly, those planetary distances taught in schools? They're the planet's average distance to the Sun.


Additionally, Venus is as fast as it will get today, too. Why is this? As a planet locked in an orbit gets farther from the Sun, the Sun's gravitational force on the planet lessens and the planet will slow down. Then, as the planet round the aphelion point and begins to move closer to the Sun, its speed will increase as the distance to the Sun decreases, culminating at maximum speed at, you guessed it, perihelion. This fact was first discovered in the early 1600s by Johannes Kepler and serves as his 2nd law of planetary motion.

Saturday, July 9, 2016

Tonight's Sky for July 9: Voyager 2 Visits Jupiter (1979)

On this date in 1979, the Voyager 2 space probe, which would become the only space probe in history to encounter all 4 gas giant planets, made its first planetary encounter when it flew past Jupiter, fifth planet from the Sun, coming within 350,000 miles of the cloud tops. While exciting in itself for professional and amateur astronomers, for the greater public, there was not an overwhelming wave of attention for this mission thanks to the fact that Voyager 1 had done the same in March.

Although observed for centuries by astronomers, the Voyagers helped scientists learn more about the planet in the 48 hours of either side of close approach than had been discovered since Galileo first turned his telescope on the planet more than 350 years beforehand at the start of the Renaissance.

In all, the Voyagers discovered volcanism on Io, a probable ocean on Europa, rings around the planet, more moons, and radiation belts, all while providing the first up close pictures of the Jovian system.
 

Friday, July 8, 2016

Tonight's Sky for July 8: Mars Sets 8 Hours After the Sun

Tonight, Mars, 4th planet from the Sun, will be setting 8 hours after the Sun, meaning that it is up pretty much all night at this point. For the record, Mars will be coming to opposition, the point in its orbit when it will be up all night, later this month.
 

Thursday, July 7, 2016

Tonight's Sky for July 7: Moon Meets Regulus

Want to see the bright star Regulus, alpha Leo, but have no idea where to look? Well, you're in luck as the Moon will be parked next to the heart of the lion low in the Western sky tonight at dusk. 

Wednesday, July 6, 2016

Tonight's Sky for July 6: Sojourner Rover Begins Exploring Mars (1997)


On this date in 1997, NASA's Pathfinder mission truly got underway as the miniature Sojourner rover drove off of its landing craft and onto t he surface of Mars, becoming the first mobile vehicle to land on another planet. Being a first of its kind mission in that it was the first rover to land on another planet and the first planetary lander to use giant airbags to cushion the landing, the world was transfixed on the mission thanks to the fact that Pathfinder/Sojourner was the first great planetary mission in the era of mass access to cable and/or satellite television as well as the Internet, which made it possible to watch live by previously unimaginable numbers of people.

As for the mission, the name was appropriate as it paved the way for the later, far more ambitious Twin Mars Exploration Rovers and (Spirit and Opportunity) of 2004 and the Mars Science Laboratory (Curiosity) of 2012. AS for this mission itself, Pathfinder/Sojourner transmitted data for 83 days (far exceeding its 30-day design life) that included roughly 2.6 billion bits of information, 16,000 images, analysis for 15 rocks, and numerous weather data measurements.

Needless to say, this was the mission that truly re-ignited the interest in planetary science that would result in a quick succession of missions culminating with the Cassini/Huygens probe, which reached Saturn in late 2004.

Unfortunately, thanks to budget cuts, NASA's ambitions of traveling to the planets and answering questions raised by the 1997-2004 series of missions will, more than likely, be restricted for the foreseeable future.

Tuesday, July 5, 2016

Tonight's Sky for July 5: Earth at Aphelion

For people living in the Northern Hemisphere, it may be hard to believe but, right now, Earth is at a point in its orbit called aphelion, which is a fancy way of saying that it is as far as it will get from the Sun. 

As for how Earth can be its hottest (at least North of the Equator) when it's at its farthest from the Sun, it has nothing to do with distance, but everything to do with geometry.

The Earth's seasons are caused by the planet's 23.5 degree tilt relative to its axis. As Earth goes around the Sun, the angle of a location relative to the incoming solar rays changes. This is the reason why the Sun apparently takes a different path through the sky (high in summer and low in winter resulting in long and short days, respectively) during the year. It is this difference in angle (and resultant day length) that causes the seasons to change.

Oh yes, Earth is roughly 95 million miles from the Sun today rather than the 93 million mile average distance taught in schools.

Monday, July 4, 2016

Tonight's Sky for July 4: New Moon

Today, the Moon, second brightest object in the sky, has reached the New Moon phase, which means that it is directly between the Sun and Earth, and thus invisible for us Earthlings as of now.

As for lunar mechanics, the Moon is always half lit. The reason we don't always see it as such is thanks to orientation in relation to us. Right now, with the Moon directly between the Earth and Sun, e can't see any of its lit side.

After today, we will see more of the Moon each night as its lit side turns more toward from us and heads toward first quarter.

Sunday, July 3, 2016

Tonight's Sky for July 3: The Dog Days Begin

It's roughly two weeks from the start of summer for us living in the Northern Hemisphere, which means that the heat is on, but it has nothing to do with a certain Dog Star. In the time of the Ancient Egypt, the people noticed that the hottest days of the year correspond to a point in time wherein Sirius, brightest star in the sky, is very close to the Sun, so close that the Egyptians thought Sirius lent its brilliance to the Sun and helped make summer, particularly the 40 days between July 3 and August 10, the hottest month of the year. 

Well, we now know that Sirius is 8.6 light years distant and plays no part in Earthly weather. Still, this is an interesting space history lesson and the explanation for a common phrase whose origin is unknown by many of the people who actually use it!


Friday, July 1, 2016

The July Sky


With the arrival of July, the Summer Solstice is still a recent memory, which means that the Sun won't be going anywhere soon. Result: those short nights are going to be sticking around, making for brief, but good times under the stars as the summer sky is, more than any other season, a cosmic picture book.

Cool Constellations
With the arrival of July, the summer sky is at its peak for viewing as all the major sights are now visible without having to stay up half the night. First of all, spring leftovers Hydra (or at least its head end),
Corvus, Cancer, Leo, and Crater will be disappearing for the year. Virgo, highlighted by bright Spica, is also getting very low in the Southwest. Also, the Big Dipper signpost is now obsolete as the last two stops in the chain are gone with only Arcturus (alpha Bootes ) and Spica (alpha Virgo ) still remaining in the sky. Back to the Dipper, it's now pointing downward come nightfall. Onto the summer sky and the cosmic picture book. First up, Corona the crown, with a little imagination, looks like its namesake, or at least a tiara. Moving over, mythological hero Hercules looks somewhat human. Continuing into the Summer Triangle, Lyra looks vaguely like an ancient lyre. Going down, Cygnus is very swan-like and Aquila, with a little imagination, looks like an eagle. The mini constellations Delphinus and Saggita? Yes, they look like their namesakes, too. Now, moving to the South, Libra, though dim, does look like an ancient string scale. Scorpius? Well, using your imagination, the profile can resemble a scorpion. Finally, Sagittarius, one look at it instantly reveals why it is nicknamed the Teapot. Also, there is the Milky Way, which arches high overhead on summer nights and serves as a good measure of how good (or bad) your sky is when it comes to light pollution. By the time the sky starts to brighten, a fall preview in the form of Pegasus, both Pisces, Cetus, Andromeda, Aries, Capricorn, Aquarius, and even Perseus is on tap, too.

Planetary Perceptions
On the planetary front, July marks a month of transition as Jupiter, which has been up for seemingly forever, is becoming a twilight object as early July offers the last opportunity to catch the planetary king under a truly dark sky. By month's end, Jupiter is strictly twilight. Additionally, for the first time in months, there are no predawn planets visible as both Mercury and Venus are in twilight, with the former making a poor twilight appearance late month and the latter making an even poorer showing at the same time. July also makes for good times when observing Mars and Saturn as both are just about due South as the sky gets dark. Unfortunately, this being summer, the planets are not all that high thanks to the flat ecliptic plane. As a final item of note, Mars is finished retrograding, which means that it will once again be converging with, and eventually passing the slower Saturn.

Tonight's Sky for July 1: Moon at Perigee
Tonight, the Moon is about as big as it will ever get thanks to the fact that the Moon is at perigee, a point in its orbit that is closest to Earth.


What many people may not realize is the fact that the Moon (and all other celestial bodies) do not orbit their parent bodies in circles, but ellipses, which are slightly elongated circles. Result: any given day of an orbital period, any orbiting body will be at a slightly different distance from its parent body. As for the Moon, this variance in orbit amounts to about 20,000 miles.

As for tonight, the Moon will be about as close to Earth as it is going to get. When it comes to practical implications, the difference will be hard to notice with the naked eye to all but an experienced observer but, in a telescope, the difference will be obvious