Red Planet Dominates Winter Skies

By Irwin Horowitz, 12-04-07

	Caption: 1997 HST Mars image

The end of the year brings with it the long awaited return of the Red Planet, Mars, to our evening skies.  On Christmas Eve, Mars will be in opposition, meaning that it lies on the opposite side of the Sun as seen from the Earth.  It will rise as the sun sets that evening and will be visible all night long, weather permitting.  It shines brighter than all of the stars in the sky (except the Sun, of course) and is only bested by the Full Moon and the morning star, Venus.

The previous evening (23 Dec) we will be fortunate to see both the full moon and Mars pass right by each other in the early evening after sunset.  If you have clear skies that night, I highly encourage you to bundle up and spend a few minutes outside marveling at the sight.  You’ll need a clear view of the northeastern horizon to enjoy this conjunction of these two celestial bodies. 

For those of you located in the northern parts of our region (Montana and the Idaho panhandle), you may see Mars graze by the southern limb of the Moon a few minutes before 7 p.m. MST (6 p.m. PST).  Not only is this a rare visual treat, but it also provides you with a sense of the motion of the Moon against the sky, as you can actually see it change position relative to the bright planet.  Note: if any of my readers finds themselves even further north that evening, they can actually see the Moon occult the planet briefly around that time.

Many of you may have received hoax e-mails in the past claiming that during its close approach Mars will appear “as big as the full moon!” As this conjunction clearly demonstrates, that claim is clearly erroneous.  The Moon is about 250x closer to us than Mars at this time, while only being about ½ the diameter of the planet.  Even when Mars had its close opposition four years ago, it was still over 150x further away from us than the Moon.

The winter solstice will occur at 11:08 p.m. MST (10:08 p.m. PST) on Friday, 21 December.  This marks the beginning of winter in the northern hemisphere and is the shortest day of the year.  The sun will set that day at 5:11 p.m. MST here in Boise (earlier for those further east) and rises the following morning at 8:15 a.m. MST for a total of over 15 hours of darkness!  Of course, we get the opposite effect in June on the summer solstice when we get 15 hours of light.

Besides Mars, the following planets are visible in the sky.  Saturn will rise about 11 p.m. MST at the start of the month and by the end of the year it will be rising around 9 p.m. MST here in Boise.  It resides in the constellation of Leo, east of the bright star Regulus.  Venus still dominates the pre-dawn sky and will remain visible in the mornings until February.  While Mars is in opposition at the end of December, Jupiter is in conjunction with the Sun around the same time, which means we will not be able to see it return to the morning skies until the spring time.  Mercury is also too close to the Sun to be observed this month.

This month’s astronomy club events in our region include the annual holiday party for the Boise Astronomical Society on Friday, 14 December at 7 p.m. MST at our usual meeting place in Classroom B of the Discovery Center of Idaho.  The Yampa Valley Astronomy Club announces a free lecture by Prof. Jimmy Westlake of Colorado Mountain College Alpine campus in Steamboat Springs on Tuesday, 04 December at 7:30 p.m. in Bogue 300.  The lecture is entitled “Are We Alone?” and will examine the factors involved in the famous Drake Equation used to estimate the number of advanced civilizations in our galaxy.  Weather permitting, there will be a telescope observing session following the talk.

I would like to wish all of my loyal readers a merry solstice and a joyous holiday season!