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Measuring the Sky
Perhaps you received that longed-for better telescope recently and want to learn more about the night skies and have no idea what to do first. May I suggest you go online to the site South Texas Astronomical Society and check out their options? There is an in-person event scheduled February 21 that just might be what you have been hoping for.
In the meantime, let us assist you to build your understanding of astronomy by providing a bit of geometry for you to use in measuring dimensions of some of the constellations visible in our winter sky. The dome of the sky, or the celestial sphere, is a circle that measures 360º. Due to the rotation of Earth on its axis, the Sun appears to move 15º across the sky in one hour. When an adult's hand is extended at arm's length in the "hook 'em horns" position, the width between the extended fingers measures approximately 15º. This is the measurement between the stars that mark the shoulders of Orion, the Hunter.
Continuing using our hands to measure, half of the pinkie measures one-half degree, the diameter of the Moon; three middle fingers clustered together mark 5º; the entire fist, 10º. It should take about six fists (like choosing up sides in a softball game when you were a kid playing for fun!) to measure from the horizon to the zenith (directly over one's head), and the angle formed by your body to the horizon to the zenith is 90º. These measurements were devised by the ancient Babylonians, who also named many of the stars and constellations while Europe was mired in the "Dark Ages". The Arab civilizations became the "keepers" and developers of Greek astronomy.
Look for Orion to become visible in the east, midway to the zenith just after sunset in the gathering darkness. Try the measurements yourself and "calibrate" your body. The redder star that marks Orion's right shoulder is named Betelgeuse, and has an apparent magnitude of 1, compared with the brilliant star Sirius just below the Orion, which is a -1. If you watch Orion through the night it appears to move from east, to south, and west over about 12 hours. It will move fifteen degrees toward west each hour. During the course of 24 hours, as the Earth turns on its axis, the stars will pass beneath us and reappear as the sun sets, to continue the cycle until Earth has moved along its revolution around the Sun. WHEW! DO go out and look up! And if you want more insider details, look for a book titled "365 Starry Nights", by Chet Raymo. It is filled with lots of interesting information and ranks high on most astronomer’s list of helpful publications. Raymo’s book is my go-to resource for easy-to-understand information such as the geometry in this column. For young astronomers I recommend H. A. Rey’s standby, The Stars: A New Way to See Them in which he creates charming stick figures to delineate the familiar eighty-eight constellations. If you read any of the Curious George books, you know H. A. Rey.
Although in general when a person thinks of a constellation they just include the specific stars that we can see with our unaided eyes as being a constellation. In actual practice, astronomers use terminology such as right ascension and declination which is similar to latitude and longitude to create complex puzzles outlining the constellations. The January issue of Astronomy magazine has a brief response to a reader’s question about them but there are also online sites to explore. I just prefer a paper and ink source instead of the internet. It is a matter of age I suspect.
Clear cold nights make for excellent viewing but your telescope and the eyepieces must be acclimated to the ambient outdoor temperatures, which means advance planning, as well as a warm jacket and a thermal cup of your favorite hot chocolate or exotic coffee flavor to help keep the chill within reason. Check how many of the Seven Sisters you are actually able to detect without your telescope and then take a look through the eyepiece. Or consider the stars in the Big Dipper asterism and the ability to detect the horse and rider in the handle bend, stars Alcor and Mizar. https://earthsky.org/brightest-stars/mizar-and-alcor-the-horse-and-rider/, my online daily star update site has more detailed information for those who want to know more than we are able to share here.
Be sure to send your email questions or comments. I do read them. carolutsinger@att.net.
Until next week, do let some stars get in your eyes.
