Greetings, stargazers.
This is the season that a lucky few of you may be receiving new astronomy toys, such as binoculars or telescopes. Or you might be looking for something for yourself or your scope-owning spouse. If so, consider an eyepiece upgrade.
Most entry- or mid-level telescopes come with economy model eyepieces. And many of those eyepieces yield a greater magnification than appropriate for their telescopes. (Interestingly, more expensive telescopes tend to be sold without any eyepiece.) The eyepiece does at least half the work in making an image for your eye to see. And nothing improves the view through a telescope better than a high-quality eyepiece.
The first thing to consider is the focal length, which determines the magnification. Bigger eyepiece focal lengths give lower magnifications. Lower magnifications give wider, and often more impressive, views of the sky.
One thing I consider important when selecting an eyepiece to put on a telescope at a star party is getting one with comfortable eye relief. Eye relief is how far from the glass you need to hold your eye in order to see through it. With enough eye relief, it is possible to look through an eyepiece even with your glasses on. You usually need to pay a premium for extra eye relief, especially with short focal lengths (i.e. those giving high magnifications).
But the easier an eyepiece is to look through, the more it will get used, and the more it is used, the better value it is.
This month
If you have never seen a comet with your naked eye, now is a chance to do it. Comet C/2013 US10 (Catalina) has made its appearance, but don’t get your hopes up for an amazing naked-eye tail. The comet is a bit over fourth magnitude. A fourth magnitude star would not even be bright enough to be included in the outlines of most constellations. Visible, but definitely an also-ran.
This morning, the comet is less than 5 degrees, or about a half a fist width, to the left of Venus. Venus is currently magnitude -4.15. On the logarithmic magnitude scale, negative magnitudes are brighter. A difference between Venus and Catalina of over eight magnitudes means that Venus is around 2,000 times brighter than the comet. So much brighter that you might even need to shield your eyes to see the comet.
Over the next few days, Catalina will be moving up and farther to the left of Venus. Moving away from the brightness of Venus will likely make it easier to see. Additionally, it will be traveling closer to Earth, so possibly getting brighter because of that.
The Geminid meteor shower, peaking on Sunday night, is usually pretty good. This year, it is only a couple of days after the new moon, so the sky should be nice and dark. If you were disappointed by the Perseids last August, this is a shower that could make up for it. But be sure to bundle up enough with lots of layers.
Don’t let a little cold send you back under the covers when there might be some great shooting stars.
Charles Hakes is a visiting assistant professor in the physics and engineering department at Fort Lewis College and is director of the Fort Lewis Observatory. Email him at hakes_c@fortlewis.edu.
Useful links
Comet C/2013 US10 Catalina: http://apod.nasa.gov/apod/ap151207.html
Astronomy picture of the day: http://apod.nasa.gov/apod/
An Astronomer’s forecast for Durango: www.cleardarksky.com/c/DrngoCOkey.html?1
Old Fort Lewis Observatory: www.fortlewis.edu/observatory
Four Corners Stargazers: http://groups.google.com/group/Four-Corners-Stargazers
