Uncle Bob's Puzzle Corner | Uncle Bob and Aunt Claire's Place | Astronomy Menu

Uncle Bob's Astronomy Pages

Summer Sky Favorites

Calling all fair-weather sky gazers. This is your season, and what a busy one it can be. We have the annual Perseid meteor shower, some deep sky objects accessible to binoculars, and the Milky Way with millions of stars in the show. The moon should be out of the picture for half of each month, and that will clear the way for finding a swarm of astronomical attractions. You will find a sky map below.

First up are the Perseids, scheduled for August 11-13. We have shooting stars every night of the year, but in addition, we have these annual concentrations because the earth in its orbit passes through trails of debris left by comets. The Perseids, once the most reliable and numerous shower, have been quiet for many years; nevertheless, at a peak rate of possibly 50 per hour in a dark site, we don't need to wait long to spy one. That's good because we have other things to see.

I'd like to relay some practical suggestions for night observation. Your night vision will improve greatly in the first 20-30 minutes, if you avoid looking at white light. If you live near street lights, find a shadow to observe from. If you are trying to read this article, or any other excellent source, while observing, you should cover a flashlight with a couple layers of red cellophane. Finally, telescope users know about dew. We pay for the warm weather when dew collects on the lens. The higher you are pointing the instrument, the faster the dew collects. If you notice it starting to collect, tip the lens down and give it a few minutes to clear. Don't wipe the glass — you might scratch it. I keep papers, books, lenses and filters in a plastic tub, and I let the lid get dewy.

Back to work. Find a dark place that has an open view to the south. Look high up in the sky. You should see two bright stars. Toward the west is the champagne-colored Arcturus, which we have seen for a good part of the spring. Almost at the zenith (directly overhead) is the bright white star Vega. Let's scan from west to east beginning with Arcturus and heading to Vega and beyond.

Arcturus is the south-westernmost star in a large kite-shaped constellation. To the east is a small hanging arc of stars named Corona Borealis (northern crown). It is one diamond-studded tiara not available through "home-shopping"; on the other hand, it's free to all sky viewers. The gems are well-protected by big strongman Hercules just to the left (east). Hercules looks more geometric than humanoid to me. Look for a quadrangle as high up as Vega and a little west. Departing each corner of the quad is a leg. They all seem to bend in a clockwise fashion. Evidently, Hercules hits the ground running. There is a globular cluster of a half-million stars (cataloged as M13) located along the western leg of the quadrangle, about one-third of the way from the north corner to the south. These clusters hover around our Milky Way galaxy. They are wildcats who refused to join the big disk, but managed to attract an impressive number of stars. At 23,000 light years, M13 is just around the corner. In binoculars, it is not a bright object, rather it should appear as a fuzzy ball and larger than a single star.

Next in our lineup, east of Hercules, is Vega, the fifth brightest star as viewed from earth. It dominates the tiny constellation Lyra (the Lyre), which is a triangle joined at one corner to a skinny parallelogram (a four-sided figure with parallel sides). Vega is the westernmost corner of the triangle, and the parallelogram hangs from the southerly corner. Look closely at the third corner of the triangle. In binoculars it is two stars; in a telescope it is four — a double-double system. Imagine waking to four sunrises all at once, or staggered throughout the day.

East of Lyra is a large constellation which suggests an elongated cross. The Northern Cross is part of the constellation Cygnus, the Swan. Imagine a large bird, wings spread, and a head at the end of a long neck, flying south. The brightest star, Deneb, is at the tail. Look at the head in binoculars. Though it is the dimmest star in the cross, it is regarded by many as the most beautiful object in the sky. It is a double star of contrasting blue and bright yellow. It requires good binoculars or a telescope to separate the two stars, but can you detect any color using binoculars? Many double stars flicker more than single stars because of the interfering light from each component. Later in the year, near Christmas time, the Swan flies down to the western horizon and disappears. It is in this orientation that Cygnus suggests the Christian cross; thus, the Northern Cross is its second identity.

Let's head southeast from Cygnus. There is another bird which appears to be flying north almost directly at the Swan. This is Aquila, the eagle. It's bright star is white Altair, and together with Vega and Deneb, it forms a large right triangle which will be visible from now through the fall and into December. They call it the Summer Triangle, probably because it dominates the high summer sky, but it runs a little late.

By now it has grown darker, and you are seeing more, and we've been steering the tour right toward the Milky Way. It's awesome. Can you see the dark lane in it which runs southward from the Swan? Why is it dark? Is it the absence of stars (negative space) or the interference of non-luminous dust? We continue south as if to look for the source of this steamy stream of stars. Who left the kettle on? We find an answer in Sagittarius, just above the horizon. It has a groups of stars known as the Teapot, and the Milky Way leads us to it and to the general direction of the center of our galaxy. Above the spout and lid of the Teapot, there are numerous fuzzy objects to look for. There are more globular clusters, M22 probably the biggest, and there are a couple of nebulas, the cloudy ghosts of exploded stars. These carry the names Trifid and Lagoon, and I have seen them with unaided eye from dark locales.

We might close by thinking about the Milky Way, and how much we have learned of our universe since the previous century began. In 1910, we had no accurate estimate of the size of our galactic disk. Harlow Shapely, theorizing that those globulars like M13 would be more numerous near the center of the Milky Way, made an estimate of the radius, and of our distance from the center. We're talking 25,000 light years. Indeed, we had no need for the term “galaxy” until astronomer Edwin Hubble found that there were others. In the 1920s, his measures of the brightness of stars in a fuzzy patch called Andromeda put their distance at one million light years, and that opened things up considerably. It is very fitting that the space telescope named to honor him is now imaging the oldest, furthest objects in our “known” universe. Enjoy.

Uncle Bob's Puzzle Corner | Uncle Bob and Aunt Claire's Place | Astronomy Menu