Bakersfield Night Sky — December 20, 2025
The William M Thomas Planetarium is closed for the winter break. Our spring shows begin in February. Bakersfield College has a hard closure (all offices closed) from this Monday, December 22 through the Sunday after New Year’s (January 4).
Tomorrow night is the longest night of the year with the December solstice that officially marks the beginning of the season of winter in the northern hemisphere. The sun has been moving southward, making lower and lower arcs across the sky during the day and it will reach its southernmost position at 7:03 a.m. Pacific time. The shallow angles of the sunlight hitting our part of the Earth dilutes the power of the sun’s energy and lower arcs across the sky mean the amount of time the sun has to warm up our part of the Earth is reduced. At the same time, those south of the equator have seen the sun making higher and higher arcs across the sky during the day with longer amounts of daylight. Both of those things are the result of the tilt of Earth’s rotation axis with respect to its orbit around the sun. On the third of January is our closest distance to the sun, so it’s clearly the angle of the sunlight that causes the cooler temperatures for us in winter.
On Christmas Eve, the moon will be just a waxing crescent among the dim stars of Aquarius, setting about 9:30 p.m., so it won’t help light Santa’s journey this year around the Earth. It looks like there is still funding for NORAD to track Santa this year. Follow along at the Norad Santa website.
On the evening of December 26, a fat crescent moon will be right above Saturn in the southwest. Saturn will be bright enough that even with a 42% lit moon, you’ll be able to enjoy seeing them both. They’ll be about two knuckles at arm’s length apart from each other, so they’ll easily fit within the same field of view of your binoculars. The following night, the moon will be at first quarter and at full phase on the night of January 2/3.
One interesting astronomy research story this past week is about the nearby interstellar clouds around our solar system that are ionized due to high-energy ultraviolet light, so the hydrogen and helium are missing one electron. Furthermore, the nearby interstellar clouds have been ionized for at least several million years. Our sun doesn’t produce the amount of UV to have zapped the gas. Other nearby sources, including three young white dwarfs (exposed cores of now dead low-mass stars), can explain some of the ionization we see but not the unusually large percentage of the helium that is ionized.
A team led by Michael Shull of the University of Colorado found that two bright stars at the paws of Canis Major could have done the job when they were much closer to the sun several million years ago. The stars are Mirzam, 493 light years away at the front paw of Canis Major, and Adhara, 405 light years at the back paw of Canis Major. These two stars are blue giant stars with between 22,000 and 25,000 times the sun’s luminosity. Now, they are quite far away but tracing their motion backwards in time, Shull et al. found that 4.5 million years ago, they would have been only 30 light years away.
At that close distance they would have been over ten times brighter than the current champion star in our sky, Sirius, also in Canis Major. Sirius is just 8 light years away but it’s a cooler, smaller star than Mirzam and Adhara. The two blue giant stars would have been as bright as Venus! They also would have produced copious amounts of UV (as they do now). Having those two stars so close to us 4.5 million years ago would have weakened the protective effect of the local interstellar clouds from cosmic rays which could have then destroyed some of the ozone in Earth’s stratosphere. That ozone is what shields us from the sun’s harmful UV. It’d be interesting to see if there is a marker of that weakening of the ozone layer 4.5 million years ago in the fossil record or other paleoclimate record.
In space exploration news, two NASA “icons of discovery”, the James Webb Space Telescope and the Curiosity rover on Mars are in TIME’s “Best Inventions Hall of Fame” that recognizes groundbreaking inventions that had the most global impact. The technological spinoffs from the development of Webb are found in improvements in the manufacturing of high-end cameras, contact lenses, and advanced semiconductors and even inspections of aircraft engine components.
Besides clearly showing us that Mars was habitable in the past, Curiosity has been measuring the radiation environment on the surface Mars—crucial measurements to prepare us for future human exploration of Mars—since it landed on Mars in August 2012 (over 13 years of data). Curiosity was the first rover to use a jetpack landing system used more recently by the Perseverance rover and will be used in the future for sending cargo to Mars. Great things are possible only when smart, passionate people work cooperatively toward a common goal.
I hope you’ll enjoy more star gazing in the longer nights of December!
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Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com
