Milky Way

If you are observing in really dark skies in March, you can see a stream of the Milky Way running between Procyon and Sirius. Courtesy

The evening skies in March offer you a very obvious contrast between seasonal constellations. The plentiful and brilliant stars that make up winter constellations are obvious in the western half of the sky, while the sparse and less brilliant stars making up the spring constellations fill up the eastern sky.

The most brilliant objects in the sky this month, in order of brightness, are Sirius, Arcturus, Capella, Rigel, Procyon, Betelgeuse, Aldebaran, Mars, Pollux and Regulus. Only one of the brightest stars this month is in the spring constellations. Why the difference in the number and brilliance of stars between the winter and spring constellations? In the winter skies, we are looking back across the nearest spiral arm of our Milky Way galaxy. When we look toward the spring constellations, we are looking directly up and out of the flat disk of our spiral galaxy. Although the spring stars and constellations are sparse and don’t have many bright stars, it does give us a clearer view of objects that lie well beyond our galaxy.

Early risers this month should watch for a tight conjunction between Mercury and Jupiter on the morning of March 5 to the ESE.

The Vernal Equinox occurs at 3:37 a.m. on March 20.

After the moon has set, the first two weeks of the month is a good time to look for the Zodiacal Lights. Look to the west after astronomical twilight. Be sure to have a dark, clear sky to see this elusive sky glow that is caused by sunlight reflecting off interplanetary dust. The Zodiacal Light looks like a faint cone of light stretching from the horizon to about halfway up the sky. It will be along the ecliptic; the apparent path of the sun through the sky.

Most everyone can find the obvious winter constellation of Orion the Hunter. However, finding his two faithful hunting dogs, Canis Major and Canis Minor, isn’t as easy because they only stick out by locating their brightest stars. Sirius shines at -1.44 magnitude, and Procyon shines at +0.4 magnitude.

If you go out in March between 7 and 9 p.m. and look due south, the most obvious constellation will be Orion the Hunter. Three bright stars in a row mark the belt of Orion, two bright stars above the belt mark his shoulders and two bright stars below the belt mark his knees. To find his two hunting dogs, all you have to remember is that they always follow him across the sky. To find his first dog, use this belt trick. Simply shoot an imaginary arrow down through Orion’s belt, and that arrow will land directly on the bright star Sirius, which marks the eye of Orion’s bigger dog, known as Canis Major. Sirius is the brightest star we can see with the unaided eye.

If you use your imagination, you can draw a stick figure of a dog nipping at Orion’s heels out of the other four to five dimmer stars nearby. Sirius is mentioned by practically every culture that ever kept records. Ancient Egypt called Sirius the Dog Star or the Nile Star, and whenever it was first visible rising before the sun in the early morning, it foretold that the Nile River would soon flood and make the land of Egypt fertile for planting.

Many of the Egyptian temples were oriented so the light of Sirius rising would flood their interiors. The expression “the dog days of summer” comes from Sirius rising with the sun in the hot months of July and August, so northern cultures associated those days with scorching heat. Sirius is such a dazzling star and low to the horizon, it can really put on a dynamic show like a disco ball where you’ll see it twinkle and sometimes give off some flashes of color.

Sirius is a blue-white star and is among the closest stars to Earth because it is located only 8.6 light years away. This means the light we see actually left Sirius 8.6 years ago. Being close to us is one reason why it appears so bright in the sky, but Sirius is almost twice as wide as our sun, and it is 23 times brighter. Sirius is the hottest and most luminous of the closest stars. Sirius has a companion star called Sirius B, which is a white dwarf. White dwarfs are stars that have exhausted the fuel in their core and have about the same mass as our sun, but they are only about the size of the Earth, making it so dense that a teaspoon of it would weigh several tons on Earth.

Sirius has some mysteries associated with it since ancient times. Many ancient writers or astronomers such as Cicero, Horace, Ptolemy and Seneca referred to Sirius as a red star. We distinctly see Sirius as a white or even bluish star. It is unlikely the star has changed color, but with the discovery of Sirius B, the companion white dwarf star, we can speculate that in ancient times Sirius B was a red giant star in its final stage of life before collapsing into a white dwarf, so maybe it was outshining Sirius at the time. Given this was only over 2,000 years ago, it seems unlikely the star would have evolved that quickly.

Another mystery is the Dogon tribe in central Africa have a legend referring to a companion star that circles Sirius every 50 years and was made of heavier materials than those found on Earth. This knowledge would not be available unless a telescope was used to find the companion star, and the composition of white dwarfs would have required some outside scientific knowledge. Were they visited by some extraterrestrial who told them about Sirius B, or did some traveling missionary visit them and pass along this information that was then incorporated into their stellar mythology?

Sirius B is dubbed the Pup, and was confirmed in 1862, almost 20 years after astronomers observed wobbles in the proper motion of Sirius across the sky. Sirius B was found to orbit Sirius every 50 years and is only visible in telescopes when it is at its farthest in orbit from Sirius.

Canis Minor, the little dog, is basically made up of two stars found higher in the sky and located by drawing a line eastward through Orion’s shoulder until you run in to the bright yellow-white star Procyon. Procyon is the sixth brightest star in our sky. Procyon means “before the dog” and rises before Sirius. Procyon is not quite as bright to the naked eye as Sirius, but in reality it is even larger than Sirius at 2.3 times our sun’s diameter.

However, Procyon is not as hot of a star as Sirius, so it shines only six times brighter than our sun. Procyon is also close at only 11.3 light years away. Ironically, just like Sirius, it also has a white dwarf companion star that is almost identical to Sirius’ companion star. Procyon’s white dwarf, referred to as Procyon B, orbits the primary star every 40 years.

I hope you catch a glance or these brilliant and unique stars this month. If you are observing in really dark skies, you can see a stream of the Milky Way running between Procyon and Sirius.

This is a monthly article provided by the Cheyenne Astronomical Society (CAS). Marcy Curran has been the editor of the Cheyenne Astronomical Society’s newsletter since 1986 and taught astronomy at LCCC from 1992-2013. For further information about the CAS, visit our website at killerrabbit.co. Our monthly meetings are free and open to the public and are held the third Friday of each month.

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