Sunday, March 1, 2015

The March Sky

With the month of March upon us, the lengthening of the days will be at its most noticeable as the Sun moves fastest near the equinox, which occurs on the 20th of the month. Besides the rapidly shortening nights thanks to the lengthening of the day, another dramatic loss in dark sky time will come on the 8th, which is when Daylight Savings Time returns. Needless to say, by month's end, there will be far less opportunity for observing as nightfall will come an hour and a half later than it did at the start of the month.

Cool Constellations
At the start of March, the first order of business should be getting a last look at the winter constellations under dark sky conditions as, with the advent of DST, most will be low in the Southwest come nightfall and, unless one has a good horizon, too low to observe very well. The early-month, early-evening observe list should include Cassiopeia, Cepheus, Perseus, Orion, Canis Major, and Canis Minor. A few other winter constellations, including Auriga, Taurus, Gemini, and the Pleiades are still reasonably well-placed, though. As Orion was to winter, the Big Dipper is to spring in that it is a signpost to the stars. Starting at the Dipper, follow the arc of the Dipper to bright orange Arcturus, alpha Bootes, and the brightest star in the spring sky. To the left of the kite-shaped Bootes, look for the arc of stars that is Corona, the crown. Next, speed onto blue Spica, alpha Virgo, and one of the brightest spring stars. Next, continue the curve to trapezoidal constellation Corvus, the crow. Finally, conclude in dim Crater the cup. Moving higher in the sky, zodiac constellations Cancer and Leo are well-placed as well. Speaking of Cancer, look just below the cosmic crab for a distinct ring of stars, the head of Hydra, the sky's biggest constellation, which snakes (sorry) through over 120 degrees of sky. For those who like to stay up late (or get up extremely early), there's mythological strongman Hercules and the Summer Triangle high overhead and, to the South, Ophiuchus, Serpens, and Scorpius

Planetary Perceptions
Like February, March is looking to be another 5 for 5 planet month. At dusk, Earth's two planetary neighbors, Mars and Venus, will continue to be easy dusk objects. As was the case last month, Venus will continue to climb out of the dusk twilight while Mars stubbornly hangs low in the Southwest, setting roughly 2 hours after the Sun all month long. Moving later into the night, Jupiter is up all virtually all night having reached opposition (the point when, as seen from Earth, a planet is 180 degrees distant from the Sun) last month. Additionally, Saturn continues to re-emerge from the Sun in the predawn sky. By month's end, the ringed wonder will be just about due South at dawn. Last but not least, speedy Mercury, which reached greatest elongation as a morning object in late February, will continue to hang around in early March. Unfortunately, thanks to the flattening ecliptic, the little planet will be very close to the horizon, making it very difficult to spot.

Young Moon Season
Want to find the Holy Grail of naked-eye astronomy? Well, you're in luck as March begins what could be considered the Young Moon season, which runs through June and features wire-thin, barely there crescents just after sunset. The funny thing: many people who call Full Moons light pollution will plan young Moon hunts weeks in advance. So, why the change in attitude?

Young Moons are, besides quite aesthetic, rare, very rare. To sight a Young Moon under 24 hours old (and even one under 30 hours old), all the conditions need to line up just right. If everything goes perfectly, on the day after New Moon, or even on the same day sometimes, just past sunset, a wire-thin crescent will pop out low on the horizon among the Sun's last rays. Needless to say, when dealing with a Moon less than 2% illuminated, binoculars are a must.
So here is why the Young Moon is so difficult to spot:

1. Timing. If New Moon is timed too close to sunset, it will be lost in the Sun's glare on the day of New Moon and will be way past a day old come the next night. A 36 hour Moon is no challenge, pure and simple.

2. Clouds. If it's cloudy, there's no seeing the Moon.

3. Light. Young Moon hunters are forced to fight twilight. With the Moon only 1-2% lit, just the act of spotting the Moon low on the horizon in such light conditions is a challenge because that is where the Sun is. A saving grace can be (and was for me both times) a nearby planet, Mercury and Venus, respectively. If you can use a bright planet as a marker, it is a lot easier to estimate where the Moon will appear once the sky gets dark enough.

4. Haze. Even more so than during the day, haze makes its presence known at dusk, looking similar to wispy clouds on the horizon. While the biggest problem during the summer, haze can even appear in winter, too. Even a crystal-clear day can produce haze on the horizon at dusk. While the haze will quickly dissipate come dark, that's too late for the Young Moon.

These difficulties compounded with horizon issues showcase why Young Moons are the Holy Grail of Lunar observers. Now for the good news: spring is Young Moon season. Because of the near vertical ecliptic at sunset, the Young Moon will hang higher in the sky now than any other time of year, which is good. For Young Moon Hunters, March through May (even June depending on time of month) is an ideal time to look. By the time July rolls around, the ecliptic is undeniably flattening too much to make observing the Young Moon really feasible.
Get out while you can!

Future thin crescents:
March 20: 17 hour Moon (telescope a must)
April 19: 31 hour Moon
May 18: 22 hour Moon
June 17: 36 hour Moon

Tonight's Sky for March 1: Venera 3 Impacts Venus (1966)
It was on this date in 1966 that Venera 3, which was set to become the first space probe to land on another planet (Venus), made a different bit of history when it crashed into the planet instead, taking the dubious distinction of becoming the first spacecraft to crash onto another planet.

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