Greetings Fellow Star Gazers!
Welcome to the third edition of Star Gazing Guide from the Milky Way Cowboys at BDSO. As we begin the last week of April, notice that our days are getting longer. Our Sun is setting close to 8:15 pm, and our first stars aren’t peeking out until around 9:00 pm. To get your eyes acclimated to the night sky, remember to avoid any lights so they can take in as many stars as possible. If you’re utilizing a night sky app, consider turning on the red light feature to preserve your night vision (scotopia).
Hopefully, you already recognize that bright non-twinkling object in the western sky as Venus. We will only be able to enjoy her magnificence for about another month, and then we’ll need to get up in the wee morning hours to see her reign in the eastern sky.
Moon-wise, we have a handsome waxing crescent that won’t impede our night sky viewing this coming week. In fact, if you have a good pair of binoculars or a telescope, the crater viewing should be spectacular.
As spring moves toward summer, we are about to lose some of our night sky favorites. Our brightest star—Sirius, Orion the Hunter, Pleiades (the Seven Sisters), and the Winter Hexagon with its bright stars and constellations, will soon be leaving us until late fall. The good news is there are
always
some fun constellations in the night sky to check out.
One popular zodiac constellation that is famous in Greek mythology is Gemini. Look for it almost overhead towards the western sky. A couple weeks ago, we shared how to find Pollux and Castor in the Winter Hexagon. If you visualize these two bright stars as the twin brother’s heads, you can follow two faint strings of stars downward. Use your sky app to help you to commit to memory the bodies of the twins. Gemini will continue to grace our night sky until late May.
Another zodiac constellation that is easy to visualize is Leo the Lion, 12
th
largest of the 88 modern day constellations. If you look overhead, you’ll see a giant backwards question mark or sickle made up of six stars. That’s Leo’s head. The nearby bright star, Regulus (with its two quite-faint companion stars), is visible on Leo’s kingly chest. And Denebola is the prominent star at the end of Leo’s tail. Those of you with telescopes might want to search out some of the galaxies and other deep sky Messier objects in Leo. Check out Leo online to learn the story of how Hercules battled the lion to the death.
In our second Guide we promised to explain how and why Polaris has not always been our North or Pole Star. Remember how we said that when you draw an imaginary line through the two stars (the Doobie Brothers) on the front of the Big Dipper’s cup, they point to Polaris, the end star in the Little Dipper’s handle. Well, if you take the two stars on the
backside
of the Big Dipper cup, they will point to the faint star Thuban (magnitude 3.65) in Draco the Dragon—our 8
th
largest constellation. Thuban was our North or Pole star from 3942 BC to 1793 BC. The reason is because during those years Thuban was the nearest visible star to the north celestial pole.
In a nutshell, here is why the identity of the Pole Star keeps changing: Earth tilts on a wobbling 22 to 24 degree axis. Every 72 years that wobbling causes a one degree change in Earth’s rotational axis. After 26,000 years, Earth will make one complete 360 degree wobble. Along the way different stars will become the new North Star. Check out the image below and you’ll see that in about 4,000 years Alderamin in the constellation Cepheus will be the North Star. And then in about 13,000 years, Vega in the constellation Lyra, and so on. Once it gets back around to Polaris, 26,000 years will have passed.
