Aldebaran Hides Behind the Moon

One of the most fascinating astronomical events late this year is the occultation, or obscuring, of a bright star by the moon. You can watch this event with the naked eye. Watch shortly after midnight as December 12 turns into the 13th, and see the moon slowly creep up on Aldebaran (the brightest star in Taurus, the Bull), finally blocking it out by 12:15 a.m. (exact time depends on your location).

Only four bright stars can ever be occulted by the moon. They are Antares in Scorpius, Aldebaran in Taurus, Regulus in Leo and Spica in Virgo. Each will be occulted in a series that repeats roughly every 18 years.

The Planets

Mercury—this elusive planet makes a brief evening appearance late in November, lying near the southeastern horizon after sunset. Not an easy object to see at this time of year.

Venus is brilliant, shining brightly in the southwest during your drive home from work during any clear evening. Its magnitude reaches –4.7 by mid-December, its most brilliant point of the year. The ease of visibility of Venus will generate the often-asked question, "Was Venus the Christmas Star?" While unlikely, the Christmas Star puzzle is an intruiging astronomical detective story told in our Christmas planetarium show each year. A lovely crescent moon joins Venus on November 3 and 4 and on December 3 in the western sky after sunset.

Mars lies quite close to Venus now, lying along the same line of sight. Of course, the two planets are not near each other in reality. By December 22 Mars lies 1.1 degrees south of Venus. Mars shines dimly at magnitude +1.2, making the brightness difference between Mars and Venus almost six magnitudes. Mars passes 0.59 degrees from Uranus on the night of December 27. Uranus is a dim 6th magnitude, detectable in binoculars or telescope, not with the unaided eye. It is staggering to realize that Mars lies a scant 192 million miles from Earth, whereas Uranus is exactly 10 times further away, at 1.9 billion miles.

Jupiter is brilliant in the constellation Capricornus. It is visible during most of the evening in November, but sets by 8:30 p.m. in mid December. Jupiter is the bright object in the southern sky, seen right after sunset. Look for the first quarter moon alongside Jupiter on November 7.

Saturn is high in the south by 10 p.m. during November, and a couple of hours earlier by December. No other bright objects lie in this region of the sky, so Saturn should be easy to spot. Through a telescope it is a superb sight, revealing the delicate ring system. Try one of our telescope observing nights to view the ringed planet.

Moon Phases

New Moon  1st Qtr  Full  Last Qtr

Nov 7  Nov 14  Nov 21  Nov 30

Dec 7  Dec 14  Dec 21  Dec 29

Planetarium Shows

Every Friday at 4 p.m. the Henry Buhl Jr., Planetarium at Carnegie Science Center presents Stars Over Pittsburgh, your weekly guide to the current night sky.

Don’t forget to see Flashback to the Future, celebrating the 40th anniversary of the Space Age, and our traditional Christmas show, The Christmas Star.

Martin Ratcliffe is the past director of the Henry Buhl, Jr. Planetarium & Observatory. He is now director of Science Theaters and Media Services, The Exploration Place, Wichita, Kansas.

Using the Star Map

Find a dark observing site, away from bright street lights and porch lights. You should also give your eyes time to adjust to the darkness. To avoid hampering your night vision and give yourself just the right amount of light for reading the map, place a small brown paper bag over a flashlight.

If you don’t know which direction you’re facing, look for the Big Dipper, or Ursa Major. Then follow the two stars at the end of the dipper’s bowl across the sky to the north star, or Polaris, and you will be facing north. East is to your right, west is to your left and south is behind you.

When you look at this map, you might think that east and west are reversed. They are opposite from the directions on a road map, but when you hold the star map over your head and look up at it, east and west fall into place. The stars on the map now should match the stars in the sky.

The north star is the only star in the sky that never moves. Throughout the night and year, all the stars move in circles around Polaris, also called the "pole star" since it is located directly over the Earth’s north pole.

As the night progresses, the stars will slowly move from east to west, circling around the pole star, or Polaris, due to the Earth’s rotation. Because the Earth is also moving around the sun, the stars appear a bit farther to the west at the same time each night.