Greetings, stargazers.
One thing I have learned when teaching astronomy is that students quite often have way cooler astronomy apps on their smartphones than I do. Faster, more accurate pointing, more object details, etc. Sigh.
Fortunately, I can introduce them to a planisphere. Known by a variety of names, such as star finder or star locator, these low-cost cardboard (or sometimes plastic) maps can show the locations of stars and constellations in the night sky at any date and time.
These portable devices don’t require a computer, a smartphone or batteries, and many versions are less than $10. The one I have now is the Edmund Scientific Star and Planet Locator, but there are a variety of other brands and sizes with lots of extra information typically printed on the back.
No matter the brand, they all work the same way. A disk has printed on it a polar projection of the brighter stars and constellations visible from mid-northern latitudes. This disk is secured within a sleeve by a grommet or rivet so it can rotate about its center point. The outer edge of the disk has 365 tick marks – one for each day of the year. The sleeve has tick marks for the 24 hours in a day. When you align the current day with the current time, a large oval hole in the sleeve reveals only the part of the disk showing the stars currently visible overhead.
If you put the finder on a table in front of you with north on the top and south on the bottom, the first thing you might notice is that east is on the left and west on the right. That is exactly the opposite of what a terrestrial map will show. However, if you hold the star finder over your head with north pointing toward north, then east will indeed be in the proper direction.
The biggest issue with a planisphere is the same one encountered when making a map of the world. When trying to display the surface of a sphere on a flat page, some parts will be distorted. In this case, the constellations toward the southern horizon will be significantly stretched. Some brands have a second opening projected from the Southern Hemisphere especially to overcome distortions seen in that part of the sky.
Venus is the evening star and will be by far the brightest thing in the southwestern sky at dusk. Mars is dimmer than it was over the summer, but is still first magnitude, and will be the bright reddish point less than 30 degrees above the horizon to the south-southwest after sunset.
The full moon this month is on Monday and is considered a supermoon. The moon’s orbit is elliptical, so has a low point, perigee, and a high point, apogee, every month. Whenever the moon is at perigee, it will appear slightly larger because it is slightly closer. If perigee happens to coincide with a full moon, it is considered a supermoon. The December full moon will also be a supermoon.
The Leonid meteor shower is a regular November event, but the peak will be only a couple of days past the full moon, so I am not expecting a major show.
If you want a binocular or telescope challenge this month, a nova in Sagittarius was recently brighter than eighth magnitude. It is toward the center of the Milky Way and only about 6 degrees from Venus. However, it is in a dense field of stars of similar brightness, so the challenge will be to know which one of those dim stars doesn’t belong.
Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory. Email him at hakes_c@fortlewis.edu.
Useful links
Planisphere:
Nova in Sagittarius:
An astronomer’s forecast for Durango:
Old Fort Lewis Observatory:
Four Corners Stargazers:
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Astonomy picture of the day:
