Greetings, stargazers.
I hope you are enjoying the change in weather. My December column has occasionally been used to list some things you might want to put on your astronomical observing wish list. This year that wish list might include a big cat.
Unless you have been shopping for one, you might not recognize “cat” as a term sometimes used for catadioptric telescope. These telescopes are simply ones that use both mirrors and lenses in various combinations to create an image.
The two main classes of telescopes are refractors, which use lenses to make an image, and reflectors, which use a large mirror to make an image. Both have their advantages and disadvantages. I have not been hesitant about my recommendation that beginners start with a good pair of binoculars, which are just a pair of small refractors. Or that Dobsonian-mounted Newtonian reflectors provide the best bang for the buck for casual observers.
Catadioptric telescopes come in several varieties that are targeted at amateur observers. The most common type is a Schmidt Cassegrain. The advantage of these telescopes is that they typically have much larger apertures, or light-gathering ability than comparably priced refractors. And they use a folded light path, so they are much more portable than a simple reflector of the same diameter. They can therefore be put on a much smaller tripod or tracking mount. Their portability is what makes them popular.
Catadioptric telescopes most often come with an electronic clock drive mechanism to allow you to find or follow your target object. Unfortunately adding one of these auto-finding drive mechanisms to a telescope can make the experience more complicated, with more time spent setting things up than observing.
- Saturn is getting lower in the western sky in the early evening, so there are only a couple of months to get a last view before it goes behind the sun.
- Jupiter, which was at opposition last month, is now very high in the southern sky in the early evening. That makes it easier to tell it is the brightest thing out there right now.
- Venus is still the bright morning star, but just not as far from the sun this month. You can see it during the daytime, as it is certainly bright enough. Its position relative to the sun won’t change during the day, so if you notice how far from the sun it is at dawn, it will remain that same distance away all day.
- The new moon this month is on Dec. 12, so that will be an ideal time to get out and find some of the dimmer things you might not see otherwise, or to watch the Geminid meteor shower.
- The Geminid meteor shower, typically runs from Dec. 7 to 17 and peaks on the evening of the 13th and morning of the 14th. Always one of the better annual meteor showers, this year it peaks on the night after the new moon. This could be one of the best chances to watch it in several years. Up to 120 meteors per hour can be expected, but to see that many, you should watch with a friend or two. My experience is that half the meteors are behind the direction I am looking. Unlike some meteor showers that are more prominent after midnight, the constellation Gemini rises soon after sunset, so these meteors should be visible all night. Most meteor showers happen when the Earth’s orbit crosses a debris trail from a short-period comet. However, this shower is from debris of the asteroid 3200 Phaethon.
- Orion is also rising soon after sunset. That prominent winter constellation, with its distinctive three bright belt stars, is a great way to orient yourself to a star chart to find other winter constellations that might not be so bright or recognizable.
Useful links:
Catadioptric Telescopes
https://en.wikipedia.org/wiki/Catadioptric_system#Catadioptric_telescopes
Geminid meteor shower
https://earthsky.org/astronomy-essentials/everything-you-need-to-know-geminid-meteor-shower/
Astronomy picture of the day
http://apod.nasa.gov/apod/
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
Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory.
