Wyoming Skies: Bright planets light up December skies

December marks the approach of the winter solstice on December 21, bringing a stretch of cold and snowy weather to Wyoming. Despite the chill, the night sky features 15 objects shining at first magnitude or brighter. In order of brightness, these include: Jupiter, Sirius, Mars, Vega, Capella, Rigel, Procyon, Betelgeuse, Altair, Aldebaran, Saturn, Pollux, Fomalhaut, and Deneb.

As night falls, the stars forming the Summer Triangle Altair, Vega, and Deneb remain visible midway in the western sky. A few hours later, Cygnus appears upright above the western horizon, highlighting its Northern Cross asterism. The lowest star of this cross, Alberio, is a striking telescopic double star displaying gold and blue colors.

High overhead, the distinctive W or M shape of Cassiopeia is easy to spot, along with the four moderately bright stars forming the Great Square of Pegasus. Nearby, the Andromeda Galaxy (M31) can be seen. Under dark skies, it is visible to the naked eye, lying over two million light-years away. Binoculars reveal more of its spiral structure.

Turning eastward, winter constellations and stars dominate the sky. The brightest object in this direction is Jupiter. Leading the winter display, the Pleiades star cluster glimmers like a tiny dipper. Below them lies Aldebaran, the fiery red eye of Taurus, with Capella shining in the constellation Auriga.

As the night progresses, Gemini and Orion rise in the east. Orion is notable for its three-star belt along the eastern horizon, with Betelgeuse marking the hunters shoulder. Nearby, Geminis twin stars, Castor and Pollux, shine brightly, while Jupiter stands out as a steady, brilliant light close to Gemini.

December evenings offer the opportunity to see two planets. Jupiter rises after sunset and remains visible until dawn, with the Moon near it on December 7. Saturn glows in the southwest as darkness falls, with the Moon nearby on December 26. In the morning sky, Jupiter appears in the western sky before dawn, and Mercury is visible in the eastern morning twilight around December 25.

The Geminid meteor shower peaks overnight on December 13-14. This reliable and bright shower is unaffected by the gibbous waning crescent Moon this year and can produce up to 120 meteors per hour under dark skies. The showers radiant rises in mid-evening and peaks around 2 a.m., allowing early evening observers to catch meteors, including long-lasting earthgrazers traveling horizontally across the sky. Geminid meteors originate from debris left by an asteroid rather than a comet.

The Ursid meteor shower reaches its peak before dawn on December 22. With a new moon two days prior, dark skies may reveal around 10 meteors per hour.

December 4 features the last supermoon of 2025, known as the Cold Moon, visible all night. Near the horizon, the Moon appears larger due to the moon illusion, though it looks smaller through a straw. The next supermoon occurs in January 2026. While supermoons do not appear larger, they do shine brighter in the sky.

Author: Sophia Brooks