Skywatch Line for Friday, October 4, through Sunday, October 6, written by Sam Salem

This is Dudley Observatory’s Skywatch Line for Friday, October 4, through Sunday, October 6, written by Sam Salem.

On Friday, Sun rises at 6:56am and sets at 6:30pm; Moon rises at 8:44am and sets at 7:07pm.

The thin waxing crescent Moon will hang close to Venus and the bright red star Antares, the brightest star in Scorpius the Scorpion on Saturday, about 40 minutes after sunset. The following evening, the Moon will lie between Venus and Antares. Venus, magnitude –3.9, gleams low in the west-southwest as evening twilight fades. It sets around twilight’s end. The dark portion of the Moon will be glowing with earthshine, the reflected light from Earth.

Mars and Jupiter, magnitudes +0.5 and –2.5, respectively, rise in late evening and show best in the early-morning sky. Watch for Jupiter to rise in the east-northeast around 10 p.m. Mars comes up almost two hours after Jupiter now, two fists to its lower left. Once they’re up, you’ll see that bright Jupiter is shining in Taurus near the Bull’s horn-tip stars, Beta and Zeta Tauri. Mars is creeping across Gemini, between the two stick-figure Twins, which are lying on their sides. Mars and Jupiter are highest toward the south around the beginning of dawn, where they shine through thinner, steadier air for the best telescopic views.

Saturn, magnitude +0.7 in the constellation of Aquarius, is a couple weeks past opposition. As the stars come out it’s already nicely up in the southeast. It’s two fists lower right of the Great Square of Pegasus, which balances on one corner after dark. By 11 p.m., Saturn is about as high toward the south as it will get.

There are three bright stars you might notice flashing or twinkling fiercely in the October night. They are Capella in Auriga, are Capella in Auriga, Arcturus in Boötes, and Sirius in Canis Major.

Look just above the northeast horizon after dark, far below high Cassiopeia, for bright Capella on the rise. Capella is the brightest star in the constellation Auriga the Charioteer. But since antiquity it’s carried the name Goat Star. Look for a little triangle of stars nearby, an asterism called The Kids. The flashes are happening because Capella is low in the sky in the evening at this time of year. When you look at an object low in the sky, you’re looking through more atmosphere than when the same object is overhead. The atmosphere splits or “refracts” the star’s light, just as a prism splits sunlight.

Arcturus is in the constellation Boötes the Herdsman. It’s an orange-colored star, in the northwest in the evening in October. You can tell you’ve found Arcturus if you notice the Big Dipper nearby. The arc of the Big Dipper’s handle can be extended outward to Arcturus. Arcturus is about the same brightness as Capella, but it’s not as noticeable. On October evenings, Capella is ascending in the sky. Arcturus is descending.

Sirius in the constellation Canis Major the Greater Dog is the brightest star in the night sky. Sirius is famous for twinkling in different colors. It is now in the south before dawn, as seen from the Northern Hemisphere. Since our atmosphere is causing the light to break into its colors, and since Sirius is often seen low in the sky where you peer at it through a thicker layer of atmosphere, the flashing colors of Sirius are obvious. When Sirius is higher in the sky, which it is close to dawn in the month of October, or in the evening sky in January and February, you’ll find that Sirius shines with a steadier, whiter light.