Stars are born, live out their life spans and then die, but the light they emit goes on forever. All the light that has ever been emitted still exists and makes up what is known as the extragalactic background light. Dr. Marco Ajello of Stanford University has used the Fermi Gamma-ray Space Telescope to measure the light from ancient stars, some dating to only 500 million years after the Big Bang, to determine the density of stars in the universe. His target was “blazars,” extremely compact quasars with black holes at the center, that boast electromagnetic emissions of energy more than a billion times more energetic than visible light. Ajello found that there are about 1.4 stars per hundred billion cubic light years which translates to an average distance of 4,150 light years between stars.

Focus on the Planets

Mercury opens the month relatively high in the southeast about two hours before dawn. It will be relatively easy to spot to the lower left of Venus until it disappears into the sun’s glare the last week of the month.

Venus is unmistakable in the southeast at dawn, where it outshines all of its neighbors. Unfortunately Venus sinks a little lower each day and will be starting to disappear into the sun’s glow by month’s end.

Mars is low in the southwest at twilight and is visible until it sets about two hours after the sun. Mars is now little more than a reddish dot even by telescope.

Jupiter rises in the east at sunset, is high in the southwest at midnight, and sets in the west at dawn. Large and bright, the giant planet will offer telescopic views of its surface features and the dance of the four major moons around and across the face of the planet.

Saturn rises in the southeast around 4 a.m. as December opens and two hours earlier by month’s end. The ring system is tilted at 19 degrees to our line of sight, making them the most open they have appeared since 2006 and offering details such as alternating rings and gaps.

Uranus is fairly high in the south in Pisces while Neptune is low in the southwest in Aquarius. Use the finder charts in the September issue of Sky & Telescope or visit to get help in spotting these far distant planets.

December events

1: Sunrise, 6:52 a.m.; sunset, 3:56 p.m. Look to the southeast about an hour before sunrise for Mercury, Venus and Saturn in an ascending diagonal line.

3: Jupiter is at opposition and moves from the morning to the evening sky. Aldebaran is to Jupiter’s lower left with the Pleiades star cluster situated well above the planet.

6: Moon in last quarter, 10:32 a.m.

9: Starting tonight the moon is high in the southeast and directly below Spica about an hour before sunrise. On Dec. 10, the moon is to the lower right of Saturn and the next night finds it to the lower right of Venus with Mercury well to the lower left.

12: The moon is at perigee, or closest approach to Earth. Since this occurs less than half a day before the new moon, abnormally high tides can be expected.

13: New moon, 3:43 a.m. This is the peak night for the Geminid meteor shower and viewers can expect a spectacular display as it falls on the night of the new moon. Look directly overhead around midnight for 80-130 bright, medium velocity meteors per hour with some having persistent trails.

18: The sun enters Sagittarius on the ecliptic.

20: Moon in first quarter, 12:19 a.m.

21: Winter solstice, 6:12 a.m. This marks the first day of winter and the Sun’s farthest point below the celestial equator. The sun enters the astrological sign of Capricornus at the solstice but astronomically has just entered Sagittarius. Venus, Mercury and Antares form a triangle low in the southeast an hour before sunrise.

25: Christmas. Jupiter is the bright “star” just above the moon. Aldebaran is the reddish star to the pair’s lower right. The moon is at apogee.

26: Full moon, 5:22 a.m. The full moon of December is called the Cold Moon, the Long Night Moon and the Moon after Yule.

31: Sunrise, 7:13 a.m.; sunset, 4:04 p.m.

Send astronomical queries to Clair Wood at or care of the Bangor Daily News, Style Desk, P.O. Box 1329, Bangor 04402.