Greetings, stargazers.
There have been many clear, dark nights recently. I hesitate to say this, but right now I think a little more light might be good for the region. But the only extra light source I am advocating is a snow-covered ground. Snow will reflect every other light source including the stars, and when the moon is out, it can seem as bright as a cloudy day. Unfortunately, the ground around my house is ominously dark and dry this month.
If you are at all romantic, you might appreciate an abundance of twinkling stars over a snow-covered landscape, but if you are an astrophotographer you quickly learn to despise the twinkles. They are just an artifact of atmospheric turbulence. After spending many years or decades traveling through space to reach Earth, it is too bad the light’s trajectory gets perturbed in the last microsecond of the journey.
The turbulence is from hot and cold packets of air mixing, compounded by the transition from flat desert to rough mountains. Light refracts differently through hot and cold air packets, and when those packets are constantly in motion twinkling is what happens. This blurs the image of a star and is the ultimate limit of resolution for any ground-based telescope.
The effect that causes the overall blurring of images is called “seeing.” The cleardarksky website link has a pretty reliable prediction for atmospheric seeing condition. I used to maintain that Durango had mediocre seeing, but I have come to look forward to days when the seeing is predicted to be as good as “average” here.
If you zoom in enough on any picture of a star, the disk will always have soft edges. The width of the star image is typically given in arc seconds. One arc second is 1/60th of an arc minute, which is 1/60th of one degree. That is the width a 0.5mm pencil lead would appear 100 yards away. If optics were the only limitation, any telescope 6 inches in diameter or larger should be able to resolve something that small. However, even the best ground-based telescopes are limited by the atmosphere to about one arc second resolution. The best resolution I have seen through the atmosphere around Durango is closer to three arc seconds. In contrast, the Webb telescope’s resolution limit is more than 10 times smaller.
Useful links
Astronomical seeing
https://en.wikipedia.org/wiki/Astronomical_seeing
Astronomy picture of the day
An Astronomer’s forecast for Durango
http://www.cleardarksky.com/c/DrngoCOkey.html?1
Old Fort Lewis Observatory
http://www.fortlewis.edu/observatory
hakes_c@fortlewis.edu
I know of no new bright comets out this month, but I did see numerous photos of Comet C/2024 G3 ATLAS from the Southern Hemisphere. I am interested to hear if anyone in the area was able to see Comet C/2024 G3 ATLAS when it was low on the horizon, as I could not.
The string of planets across the evening sky is still out. Venus and Jupiter are the brightest, and Sirius is the only star that is brighter than Mars right now.
Mars is nearing the end of its retrograde phase – when it appears to move from east to west against the background stars. This month, it is near Castor and Pollux, the twins of Gemini. If the seeing happens to be exceptional, maybe you can see some surface details through a telescope.
Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory.
