EDITOR'S NOTE: This monthly guide to the stars is from the Marshall Martz Memorial Astronomical Association, the Southern Tier Astronomy Recreation Society, and the OBSERVER. For further information, contact the M.M.M.A.A. at www.martzobservatory.org or S.T.A.R.S. at ww.UpStateAstro.org/stars/stars.html
By RONALD W. KOHL
Special to the OBSERVER
During the last few days of December, it may be possible to spot little Mercury low in the southwest evening twilight. Use binoculars and look just below the much brighter Jupiter. On Dec. 28, the moon will join these two planets, very low in the southwestern sky.
Brilliant Venus appears as the Evening "Star" all month long, shining in the southwestern twilight sky. On New Year's Eve, look for the moon just above Venus.
Mars remains behind the sun and is not visible this month.
Bright Jupiter can be seen in the southwestern evening sky, drifting lower each night. On New Year's Eve, Jupiter and Mercury will be very close, low in the southwest.
Saturn rises in the east around midnight and is high in the south at dawn. In a fairly large amateur telescope, the nearly edge-on rings look like a thin disk that bisects the planet's globe. With the glare from the rings gone, now is a good time to search for some of the dimmer moons.
The Geminid Meteor Shower peaks in the predawn hours of Dec. 14. However, this year, a bright moon will drench the sky with light, drowning out all but the very brightest meteors.
The sun reaches the Winter Solstice on Dec. 21 at 7:04 a.m. This is the beginning of winter in the Northern Hemisphere and summer south of the equator.
Mergers and Acquisitions
The universe is truly stunning and magnificent but it is also very violent and deadly. Since ancient times, humans have always attempted to attach the intent of a supernatural mind to all that occurs in the Natural World. For this reason, they have invented innumerable gods and countless creation stories and myths. It's extremely difficult for many people to comprehend that the universe is completely indifferent to the existence of humans and all other life forms.
We live in the Milky Way Galaxy, a giant assembly of gas, dust, and hundreds of billions of stars, all held together by gravity. A little over two million light years away lies the Andromeda Galaxy, another spiral galaxy that is quite similar in size and shape to the Milky Way. That is all well and good but there is a problem. These two tremendous galaxies are on a collision course, approaching each other at a speed of nearly 315,000 mph. We know this because the spectral lines of the light coming from the Andromeda Galaxy are displaced toward the blue end of the spectrum. In other words, Andromeda's light is blueshifted by the Doppler effect. Over the next 3-5 billion years, our Milky Way Galaxy will collide and then merge with the enormous Andromeda Galaxy, and the eventual result will be the formation of a single gigantic elliptical galaxy. During the several near misses prior to the actual merger, the forces of gravity will twist and tear long tidal tails and plumes of stars, gas and dust from each galaxy, greatly distorting their original disk-like shapes.
When I show images of galaxy collisions to people visiting my observatory, one of the most frequently asked questions concerns the chances of collisions between stars during the merger process. Actually, although galaxies are gigantic and they contain billions of stars, they are really mostly empty space. The distance between individual stars in a galaxy is so incredibly huge, the probability of stars physically colliding is very small. As an example, if our sun was the size of a golf ball, the nearest star (Proxima Centauri) would be another golf ball almost 1,000 miles away. And that example represents the nearest star to our sun.
Although there is plenty of room for billions of galaxies in the universe, they still smash into each other surprisingly often. All galaxies are in constant interaction with other galaxies and clusters of galaxies through gravitational attraction. Even though most galaxies are rushing away from us due to the expansion of space, the Andromeda Galaxy is close enough to the Milky Way for gravity to overcome the expansion force. When the collision event finally begins, the two giants will undoubtedly not merge on the first pass but will probably simply brush past and circle around each other, causing gravitational distortions. However, their mutual gravity will eventually triumph, drawing the two galaxies together on successive flybys. Astronomers already have a name for the new elliptical galaxy that the mega-merger will create. They have named this future galaxy "Milkomeda."
