Autumn skies are a great time to learn some stargazing basics to help you around the night sky. And it is easy to find star charts, whether old school at the library or downloading an “app” for your Smartphone.
First observation: You never see the Moon or a planet in the north part of the sky. Most of the Solar System objects are seen by facing south and looking up, not facing north. That includes the Sun, Moon and five naked eye planets. Exceptions are some comets and asteroids.
That’s because Solar System objects orbit the Sun in a narrow plane. From Earth, that pathway across the background of stars is called the Zodiac, and it circles the sky within the boundaries of 13 constellations. In astrology, Ophiuchus the Serpent Bearer between Libra and Scorpius, is not included. The planet Saturn has been in Ophiuchus all Summer of 2017. And the Sun does spend a week in this “extra” constellation of the Zodiac.
On any clear night, from a dark location, the naked eye can see about 2,000 stars. You might be lucky to see 200 from an urban, light polluted site. Their patterns, immortalized in mythical tales thousands of years ago, were given official, arbitrary boundaries only in the last 300 years.
There are 88 constellations in the northern and southern celestial hemispheres. About one-third are never seen from geographic latitudes higher than 30 degrees—like we stargazers in the Mountain Empire.
The stars to the north circle around the North Star, Polaris. In the early Autumn the “M” shape of Cassiopeia is high in the northeast, while the bowl of the Big Dipper is dragging along the northwest horizon. The faint stars of Draco the Dragon wanders between them.
These stars and their constellation patterns in the north are called circumpolar—they never set below the horizon. The Big Dipper and the Little Dipper are just parts of a constellation, and as such, are called “asterisms.” The Big Dipper is part of Ursa Major, the Big Bear, and the Little Dipper is part of Ursa Minor, the Little Bear.
The North Star is the tip of the Little Bear’s tail, or the end of the dipper’s handle. It is, in fact, a not-so-bright star that is famous only because our spinning axis points to it.
That polar axis of Earth actually wobbles, like a lazy top. Called precession, the wobble makes a complete circle every 26,000 years. So, Polaris is only a temporary “North Star.” In about 7,000 years, the very bright star in the west Autumn skies, Vega in Lyra the Harp, will be directly north, unmoving as a spectacular guidepost to the pole. There is no naked eye star near the south celestial pole, which is located in the constellation Octans the Octant—a forerunner of the navigational sextant.
The brightest star of any constellation is designated “alpha.” Then, the next brightest stars are given the next letter in the Greek alphabet—beta, gamma, delta and so on to the 24th letter omega.
Of course, many of the brightest stars are named. Nearly three-fourths of all named stars can be traced back to ancient, Arabic words describing a part of the constellation.
Like Enif, the “nose” of Pegasus the Horse.
Or the more familiar stars like Deneb (tail) in Cygnus, Altair (flying eagle) in Aquila and Betelgeuse (armpit of the giant) in Orion. Libra the scales, known to the Greeks as the “Claws of the Scorpion,” called the alpha and beta stars of this constellation Zubenelgenubi (the southern claw) and Zubeneschamali (the northern claw)—quite a mouthful!
Distance between stars is measure in degrees, with half the sky from horizon to horizon being 180 degrees. From horizon to directly overhead, zenith, is 90 degrees. There are many asterisms in night sky that are good guidelines for distance. The pointer stars of the Big Dipper are five degrees apart. One side of the Great Square of Pegasus is about 10 degrees.
Since each human has a body features in basically the same proportions to their size, a hand stretched out at arm’s length will give everyone the same measuring guideline.
A thumb extended to arm’s length will block out about one degree of the sky. A clinched fist will block out about 10 degrees of the sky, and a spread hand from the top of the thumb to the little finger will measure about 20 degrees.
Incredibly, the Sun and Moon block out only one-half degree of the sky—a little pinky! Yet, their presence always dominates our attention skyward.
Now you have some simple tools for stargazing, and using them qualifies you for the title “amateur astronomer.” Bundle up these Autumn nights, grab a star map and enter the Universe right in your own backyard.