The October sky
October is a great time to venture outside and find the Milky Way. Away from the city lights, you should be able to find the cloudy ribbon that makes up our home galaxy overhead. For observers in the Northern Hemisphere, the brightest part of the Milky Way is in the constellation of Sagittarius, near the star Al Nasl. This region is roughly the center of our galaxy.
Our view from Earth takes us through the Sagittarius arm, one of the prominent spiral arms of our galaxy. Although studded with star clusters and glowing nebulae, the Sagittarius arm is also clouded with vast amounts of interstellar dust. This prevents us from looking through the Sagittarius arm to see the galactic center itself. At the center, we would find the Sagittarius Star Cloud, about thirty thousand light-years distant. The Sun and all the stars in the outer part of the galaxy revolve around this spot, which is believed to contain a massive black hole. At the rate of 155 miles per second, it will take Earth and Sun about two hundred million years to complete one orbit.
Number 7: Rigel—Magnitude 0.12
Rigel shares the sky with Betelgeuse in the constellation Orion, and forms Orion’s western foot. According to mythology, this is the point where the scorpion stung the great hunter. Actually, Rigel is a multiple-star system. Rigel A shines forty thousand times stronger than the Sun. A heavy star, Rigel A is likely to end its life in a supernova in a few million years or so.
Number 6: Capella—Magnitude 0.08
Look for Capella, a brilliant star with a distinct yellowish hue, in the constellation Auriga, the Charioteer. Capella measures sixteen times larger than our Sun in diameter; it is 174 times as luminous, and is located forty-two light-years away. It is a fascinating star system comprised of two similar class G yellow giant stars and a pair of much fainter red dwarf stars. Capella appears to rise well to the north of due east. In fact, it is visible in the lower forty-eight states throughout the year. To locate it, follow the two top stars that form the pan of the Big Dipper across the sky. Capella is the brighter star in the irregular pentagon formed by the stars in the constellation Auriga.
Number 5: Vega—Magnitude 0.03
The brilliant bluish-white star in the constellation of Lyra, the Harp, is Vega. It’s the third-brightest star visible from mid-northern latitudes, behind Sirius and Arcturus. Vega is also the brightest of the three stars forming the large Summer Triangle. This hydrogen-burning dwarf star is fifty-four times more luminous and 1.5 times more massive than the Sun. At a distance of only twenty-five light-years, it’s a near neighbor. In 1984, a disk of cool gas was discovered surrounding Vega, extending some seventy Earth-Sun distances from the star. It was not by chance that Carl Sagan selected Vega as the source of radio transmissions received from an advanced alien culture when he wrote the book that was the basis for the movie Contact. A “hole” was found in the Vega disk, indicating that planets might have coalesced and formed around the star.
Orionid Meteor Shower
The Orionid meteor shower peaks around 21-22 October each year. This is one of the two meteor showers associated with Comet Halley. Orionids tend to travel quite long distances, and often leave trails, which can sometimes be visible for several seconds. Look for about ten meteors per hour with surges to twenty-five per hour.
Where Are the Planets and the Moon?
- Look for Mercury early in the month hugging the eastern horizon in the morning twilight.
- Venus is the evening star, setting around 7:00 p.m.
- Mars is still brilliant, setting about 3:00 p.m. Mars sits one degree north of the Moon on October 6.
- Jupiter rises a few of hours before the sun. See Jupiter four degrees south of the Moon on October 21.
- Saturn is a great object to view through your small telescope, with its rings still open toward Earth. It rises about 11:00 p.m. Find Saturn five degrees south of the Moon on October 17.
- The full moon is on October 10. The new moon is on October 25.
One light-year is equal to 5.88 trillion miles, the distance that light travels in one year.