What's Up in the Night Sky

April 2013 - Vol. 17, No. 4

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.

Look S as night falls to see the brightest star of the evening, Sirus (Canis Major). Look to its upper right to find the familiar "hour glass" asterism of constellation Orion with bright white Rigel (lower right) and red Betelgeuse (upper left). Below the three Belt stars, lies the Great Orion Nebula (M42 & M43) visible to the naked eye as a hazy patch of light. Now shift your gaze to the left to find another bright star, Procyon (Canis Minor) the upper star of the "Winter Triangle" mentioned last month. Above Procyon, and to its left, Saturn glows brightly and above Saturn at to its right are the Gemini twins, Pollux and Castor. As the month progresses and winter becomes spring, orange Aldebaran (Taurus) comes into view to the W. Just to the left of Aldebaran, a star cluster, the Hyades, might be faintly visible under dark sky conditions. Above that glows the more famous cluster, the Pleiades (M45). Although smaller that the Hyades, it is much brighter and should be visible as another hazy patch of light. Some may even be able to make out the tiny "dipper" arrangement of its eight brightest stars. High above and a bit to the right is brilliant Capella (Auriga) and farther right is the famous "W" asterism of Cassiopeia.

MERCURY favors observers in the southern hemisphere this month.. VENUS returns to the evening sky late this month moving into the night sky after conjunction. JUPITER will be visible in the evening sky, moving toward conjunction with the Sun next month in sets before midnight. MARS will not be visible this month, it reaches astronomical conjunction with the Sun on April 18. SATURN reaches opposition this month in the constellation of Libra.

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	Jupiter will be near Aldebaran this evening and for the next few days. They will be joined by the Moon on April 14.
08	Mercury 7 deg. S of Moon. You'll have to have a good horizon and get up before the Sun.
14	Jupiter 2 deg. N of the Moon.
15	Moon at apogee.
18	Mars in superior conjunction with the Sun, will not be visible this month.
19	Mecury 2 deg. S of Uranus
20	Astronomy Day
22	Lyrid meteor peak, calculated rate of this shower is 20 meteors per hour. This year, the Moon interfers as it will be well passed first quarter. The best time will be in the last few hours before dawn.
24	Jupiter 5 deg. N of Aldebaran.
26	Saturn 4 deg. N of the Moon.
27	Moon at perigee.
28	Saturn at opposition.

Lunar Almanac for April 2013

Phases of the Moon	Phase and Date(s)	Best viewed before local midnight
	New 10	Deep Space Objects
	1st. Qtr 18	Planets & Moon
	Full 28	Moon
	Last Qtr 03	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