THE USM SOUTHWORTH PLANETARIUM
207-780-4249 www.usm.maine.edu/planet
70 Falmouth Street Portland, Maine 04103
43.6667° N 70.2667° W
Altitude: 10 feet below sea level
Altitude: 10 feet below sea level
Founded January 1970
Julian date: 2458602.35
"“Dwell on the beauty of life. Watch the stars, and see yourself running with them.”
THE DAILY ASTRONOMER
Monday, April 29, 2019
Sirius Matters
Sirius, the dog star, represents the nose of Canis Major,
the larger of Orion's two hunting dogs. One will find it
in the western evening sky each night for the next few weeks.
Seek out Sirius while you can. This evening it will lurk low in the western evening sky. Thought it is the night sky's brightest star, its position makes it somewhat difficult to observe. After all, May is less than 36 hours in the future and the winter stars will soon be exiting stage west. Of course, Sirius and its coterie of winter stars will return to the early morning mid to late summer sky. (The less said about that..)
As Sirius prepares to set, we should devote a few moments to marvel at this remarkable star.
First, its "nearness." At a distance of 8.7 light years, Sirius is one of the ten closest stars to us. Yet, how close is it really? Please try a demonstration. Read the following word: Sirius.
Yes, that task was quite simple. During the brief moment you needed to read that word, copious amounts of light left Sirius' photosphere. By the time you finish reading this sentence, that light will already be more than 3 million miles away from that star. A minuscule amount of that light will reach our solar system in mid January 2028! That light is now about 10 million miles away from Sirius and is moving through space at 186,290 miles per second. (If you are wandering outside in the early evening in mid January, 2028, you might see some of the photons that departed Sirius when you read "Sirius."
Next, its history. Sirius also served as the dog star in ancient Egypt. Many of those ancient Egyptians logically believed that Sirius bestowed an abundance of heat on us, as well as light. They reasoned that the Sun was bright and quite hot, so, too, would the star Sirius, as it was the brightest night sky star. Based on this mistaken, but understandable, presumption, they concluded that summer was so hot because at that time the Sun and Sirius were in the same part of the sky and so Earth was receiving the combined heat of both bodies. While this theory was incorrect, we do receive some heat from Sirius: equal to the light of a candle at a distance of three miles.
Finally, Sirius is the ultimate celestial time keeper. It reaches midnight culmination on January 1st, meaning that it crosses the meridian on the first moment of the year. As stars rise about 4 minutes earlier each day, Sirius crosses the meridian at 11:56 a.m. the following night. Sirius is now low in the southwest in the early evening, making the arrival of mid spring. It will emerge in the southeastern late summer sky and will eventually move into the winter evening sky and, yet again, reach midnight culmination on New Year's. Sirius' brightness and its favored position at year's beginning have elevated Sirius into a special stellar category.
We'll watch it each night as it draws closer to the setting Sun, destined to return to prominence next winter.