What's Up in the Night Sky

May 2013 - Vol. 17, No. 5

This Month's Night Sky - NOTE: The next paragraph describes the sky as it appears at 10 pm EST (11 pm EDT) near mid- month. The sky also looks this way at 11 pm EST (midnight EDT) during the beginning of the month and at 9 pm EST (10 pm EDT) by month's end.

As May brings the lengthening days, the hours of nightly observation decrease as well, it is always with a bit of sadness that we say good-bye to the Winter and Spring constellations, Gemini, Leo, and Virgo. The early evening presence of Arcturus, the second brightest star in the northern sky, reminds us that the bright star clouds of the Milky Way will soon be brightening up those dark evenings when the Moon is small enough to allow us to truly enjoy those galactic treasures. As the evening turns to morning, the bright stars of the summer triangle follow until just before sunrise, the Milky Way is at the zenith, high overhead. Long twilight hours come to the northern hemisphere.

MERCURY returns to the evening sky the last week of the month to put on a great show with VENUS and Jupiter in the evening sky. VENUS returns to the evening sky but hugs the horizon for northern observers. JUPITER is visible in the early evening, vanishing before twilight ends. MARS still hides in the Sun and won't be seen until late June. SATURN still visible most of the night, fades before sunrise.

Review how to determine Angular Measurement.

Calendar of Events

NOTE: For those observers not in the ET zone, convert the calendar times to your zone's time by subtracting one hour for CT, two for MT and three for PT. Don't forget to adjust for Daylight Savings Time when necessary by subtracting one hour from your planisphere's time. Dawn and dusk times must also be corrected. See your local newspaper, TV news, or cable TV's Weather Channel for sunrise and sunset times. Unfortunately some of these events may occur during daylight hours in your area.

DATE	EVENT
05	Eta Aquarid meteors, showers up to 60 per hour at zenith, Moon favorable.
10	Annular solar eclipse, visible in Australia and south Pacific islands.
11	Mercury at superior conjunction.
12	Jupiter 3 deg. N of the Moon.
14	Moon at apogee.
22	Spica just S. of the Moon, occultation in SE Asia and NE Australia.
25	Mecury 1.4 deg. N of Venus
26	Moon at perigee.
27	Mercury 5 deg. N Jupiter,
28	Venus 1 deg. N of the Jupiter.

Lunar Almanac for May 2013

Phases of the Moon	Phase and Date(s)	Best viewed before local midnight
	New 09	Deep Space Objects
	1st. Qtr 17	Planets & Moon
	Full 24	Moon
	Last Qtr 02	Deep Space & Planets

Topic of the month: Ursa Majoris

Spring brings attention to a familiar constelation, Ursa Major, the Great Bear. This time of year, the bowl of the Big Dipper, is hanging below the handle for in the early evening hours. The name, " Big Dipper" is called an asterism, because it doesn't include the entire constellation, but a few bright stars that are popularly associated with a familar object or form. Although the constellation is associated with a bear, it's a bit of a mystery because the handle of the dipper is allegedly the tail of the bear, but, interestingly enough, bears don't have tail. The constellation is circumpolar for observers in the northern hemisphere, this means that it never sets, but continuously circles around the north star and doesn't go below the horizon.

Why is it considered a spring constellation, then? Spring is the majical time of the year when deep sky astronomers look for galaxies, especially those that are associated with the Como and Virgo clusters of galaxies. There are a number of galaxies in Ursa Major that backyard astronomers love to look at. The brightest of these are known as M81 and M82. These galaxies are nearby on a cosmic scale, M81 is a beautiful spiral galaxy of type Sa, due to the large size of its central nucleus. It is the largest galaxy in a group of galaxies that are actually gravitational bound to each other about 12,000 light years away. .(Click on the link to see the APOD image of the M81 group.) M81 and M82 are well known interactive galaxies. They are in orbit around each other and the larger spiral has "stolen" matter from the irregular M82. There is a bridge of hydrogen gas between them that has been detected by x-ray telescopes.

.Ursa Major is a constellation of second magnitude stars. The central star of the handle of the Big Dipper is called Mizar. If you look closely you will see that Mizar has a companion star. The name of the companion star is Alcor. The two stars are a good test for far eyesight. The seven bright stars that make up the Big Dipper were the inspiration for Vincent Van Gogh's Starry Night painting. Alpha Majoris, Dubhe, and Beta, Merak are the two bright stars on the far end of the cup of the dipper. These two stars are also called the "Pointers" because following a line from the bottom of the cup toward the rim will reveal the location of Polaris, the north star.

--See You Under the Stars!
Astra for Astra's Almanac