Sunday, May 1, 2016

The May Sky 2016

With the arrival of May, the news is of a very mixed nature. First, the bad. While the lengthening of the days (and shortening of the nights) will slow, that is little consolation for astronomers as, by this time of year, the nights are getting rather short and staying up to view under dark skies is undeniably a chore for most. Ditto for getting up early for early bird observers. However, the good news is threefold. First, the rate of cloudiness will drop as it did last month. Second, May will finally bring consistently warm nights where bundling up is no longer a must. Third, at least at the start of the month, the bugs shouldn't be much of an issue, either.

Cool Constellations
By the time May arrives, most of the winter constellations are a memory. Still hanging around low in the West are Auriga and Gemini, but they won't last much longer. Also, barely circumpolar Cassiopeia is now just scraping the Northeastern horizon, too. By the time May comes around, there is no better time than now to use the handy Big Dipper signpost. 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 and looking in the South-Southwest, zodiac constellations Cancer and Leo are still well-placed, but this will be ending come next month. 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 later, there's mythological strongman Hercules and the Summer Triangle high overhead and, to the South, Ophiuchus, Serpens, Libra, and Scorpius are all starting to rise at a somewhat reasonable hour. By the time the sky starts to brighten, Vega is at Zenith, Sagittarius is due South, and the Great Square has reemerged in the East.

Planetary Perceptions
On the planet front for May, Mercury is the star, or planet, of the month. The first order of business should be to catch speedy Mercury in the dusk twilight. The little planet put on its best evening appearance of the year last month but, come May, it's quickly dropping out of the sky as it heads toward solar conjunction, from which it will appear as a morning object in the final days of the month just ahead of the rising Sun. The real big news here: on May 9, Mercury will transit the solar disc as it comes directly between the Sun and Earth, appearing as a tiny silhouette against the backdrop of the Sun thanks to lucky celestial geometry. The vast majority of the time, Mercury, as seen from Earth, passes above or below the Sun, but not this time. The next transit of Mercury will not occur until 2019. Moving into the night, Jupiter, which reached opposition on March 8 is extremely well-placed as the sky is getting dark as it just about crossing the meridian, and is thus at its highest. As an item of note, the sky need not be truly dark to get good views of planets. In fact, twilight commonly offers windows of steady air, making viewing planets at high power much, much easier. Later in the night, Mars is next to break the horizon, followed closely by Saturn. An item of note: these planets had been converging the past two months. Now, with Mars retrograding, period over, Mars is now putting sky between itself and Saturn, which will continue through June. Additionally, Mars comes to opposition the 22nd, meaning that it is directly opposite the Sun in the sky as seen from Earth, meaning that Mars is up all night. Moving to the immediate predawn sky, it will take eagle eyes and probably optical aid to spot Venus, which is barely visible at the start of the month and lost in the Sun's glare by mid May.




Tonight's Sky for May 1: May, Cross Quarter Day
Today is May Day and also a cross-quarter day. What is a cross-quarter day? It's the mid way point of any season and was, like the solstices and equinoxes, an important time for early civilizations as these days served as another natural way to divide up the year into periods of time, which became a matter of life and death with the advent of large scale agriculture around 5000BC.

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