When first learning to identify objects in the night sky, novice stargazers should start their observations before it gets completely dark. The planets and brightest stars will be visible, but not much else. Right now, Jupiter is dominating the southern sky and is the brightest thing in the evening when the moon isn’t out.
Two bright stars to look for at dusk are Arcturus and Vega. After Sirius, which isn’t out right now, Arcturus and Vega are the second and third brightest stars visible from Durango. You can find Vega shortly after sunset when you look about 30 degrees above the northeastern horizon. Arcturus will be the very bright star a little to the south of your zenith point, or the point directly overhead.
Another way to find Arcturus is to remember that the handle of the Big Dipper will “Arc to Arcturus.” The second half of this memory aid, and a way to find another bright star, is that if you continue the arc through Arcturus from the Big Dipper, you will “speed on to Spica.” Most of the time, Spica will be the next bright object you encounter toward the south, but right now, Jupiter happens to be that direction, too. And Jupiter, at magnitude -2.21 is about 20 times brighter than Spica.
I like to contrast the color of Vega with that of Arcturus. Both stars are very close to the same brightness, at magnitude 0.0, but Arcturus is noticeably yellower than Vega.
Vega is one of the most studied stars. It is close enough to the sun to determine its distance using parallax. It shows a tiny but measurable shift in position relative to more distant background stars when viewed at different times of the year, when the Earth is on different sides of the sun.
Vega has a very flat spectrum. That means it shines with equal intensity through the commonly used ultraviolet, blue and yellow filters. It also shows very little changes in intensity over time. In fact, Vega was a primary star used to define the modern logarithmic magnitude scale. It is magnitude 0.0.
For Northern Hemisphere observers about 12,000 years ago, Vega would have been the pole star. This is because of the precession, or wobble, of the Earth’s axis. In another 14,000 years, it will again be the pole star.
Vega is the brightest of the three stars in the summer triangle, the others being Deneb and Altair. These stars make a good starting point for locating other stars and constellations in the summer sky.
This monthJupiter is the brightest object in the southern evening sky. Through a small telescope, you can easily see the Galilean moons and usually at least two cloud bands that look like stripes going across Jupiter. With an 8-inch scope, you might see more bands or even a shadow of a moon as it happens to pass in front of Jupiter. The Great Spot would be more of a challenge, as you would need to check when it is in an optimum viewing position. I would not expect to see it as a red spot though – just a slightly different shade of beige.
Saturn is rising in the southeast. The rings are at a nice angle for viewing, and they can be seen with very low magnification.
Venus is the morning star. This is a good month to see Venus during the day. The easiest way to do that is find it at dawn and keep following it as the day gets brighter. At brighter than magnitude -4.2, Venus is by far the brightest thing in the sky besides the sun and the moon. It will stay the same distance from the sun, so as the sun rises and moves across the sky, Venus will stay the same distance ahead of it.
Keep checking the Four Corners Stargazers Google group or Facebook page for updates on summer stargazing activities. I hope to see you at one of these events.
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 [email protected]