Astronomy in October

Starry night in October

October’s Skies Are Great For Stargazing

Posted on Friday, September 26, 2014 by eNature

October skies are busy ones! The longer nights and cooler, clear skies of fall make for some great stargazing. And there’s a lot more than just stars to see up there!

Highlights Include Stars, Planets And Well-known Constellations

Our night sky sparkles with stars, billions of them, inspiring lovers, poets, explorers, and scientists. The closest star to Earth, the Sun, warms our planet and makes life possible.

Stars are composed mainly of hydrogen gas. Their light comes from the energy produced at their cores by nuclear fusion. This energy emerges from the surface of a star as the light we see and as ultraviolet light, X rays, and radio waves.

Our sun, which is at a stage in its life (called the main sequence stage) when it converts hydrogen at its core to helium and energy, maintains a fairly steady energy output. It’s been at this stage for about four and half billion years, and perhaps another five billion years remain until it uses up its hydrogen fuel. When a star becomes exhausted, the fuel at its center begins to expand and its surface cools. Depending on its mass, the star then turns into a red giant or a supergiant. Our sun will become a red giant.

In a red giant, both helium and hydrogen are transmuted into heavier elements and energy. After swelling to many times its former size and using up its store of helium, a red giant sheds its outer envelope. The star’s interior begins to shrink, and its surface heats up, becoming white hot. It’s now a white dwarf, an extremely dense star with the approximate mass of the Sun compressed into a size about that of the Earth. A teaspoonful of the matter of such a star would weigh many tons.

October Constellations

The Summer Triangle still graces the sky in early fall. At 9:00 p.m. on October evenings, it lies in the northwestern quadrant of the celestial dome. One corner, Altair, the alpha (or brightest) star in the constellation Aquila, the Eagle, is almost due west. Vega, the blue-white alpha star in the constellation Lyra, the Harp, is about halfway up the northwestern sky. The third corner, marked by Deneb, the brightest star of Cygnus, the Swan, is about two-thirds of the way between the horizon and the zenith (the point straight overhead).

Hercules, the Strongman, lies low in the northwest, just below Vega. Ursa Major, the Great Bear, and its well-known asterism (a star shape within a larger constellation), the Big Dipper, are very low on the northern horizon. The Little Dipper, or Ursa Minor (the Little Bear), extends to the left of Polaris, the North Star, which marks the end of its handle.

In the northeastern quarter of the sky is Andromeda, the Princess. Nearby are her mother, Queen Cassiopeia, whose wide W shape is now angled like a number 3, and her father, King Cepheus, shaped like a child’s drawing of a house. Below the Princess and the Queen is Perseus, the Hero, who saved Andromeda from Cetus, the Sea Monster. The brightest stars in this part of the sky are the yellowish star Cappella, the alpha star in the pentagonal constellation Auriga, the Charioteer, and the reddish star Aldebaran, marking the eye of Taurus the Bull, low in the east. The V-shaped star cluster of the Hyades looks like an arrowhead pointing to the right. Aldebaran sits at the end of the bottom arm of the V. Above Aldebaran is the small but beautiful star cluster of the Pleiades, also known as the Seven Sisters.

High in the south and southeast are the stars of Pegasus, the Winged Horse ridden by Perseus. The curved, narrow A shape of Andromeda begins at the northeastern corner of an asterism called the Great Square of Pegasus and stretches into the northeastern sky. On a very dark, clear night you might be able to make out a fuzzy patch of light above the middle of the two lines of stars that form Andromeda; this is the Great Andromeda Galaxy, the most distant object the eye can see unaided by binoculars or a telescope.

Closer to the horizon in the southern part of the sky are Pisces, the Fish, and below it, the dim constellation Cetus, the Sea Monster. Culminating in the south is Aquarius, the Water Bearer. Capricornus, the Sea Goat, and some of the other faint “watery” constellations, including little Delphinus, the Dolphin, are in the southwest. Almost due south is one of the brightest stars in the sky, Fomalhaut, the alpha star in Piscis Austrinus, the Southern Fish. Fomalhaut is unfamiliar to most northern-latitude observers since it belongs to a Southern Hemisphere constellation that appears in northern skies only briefly and always low. There are no other bright stars in the southern sky at this time, so it’s unmistakable.