This is a splendid month for stargazers. Brilliant Venus shines in the southwest after sunset all month. Nearly as bright, Jupiter rises high in the eastern sky in the early morning hours and passes within a hair’s breadth of the star Wasat in the constellation Gemini. On October 12, three moons of Jupiter cast shadows across the face of the planet. Uranus reaches opposition and passes an orange 6th-magnitude star in Pisces, which makes it easier to see the blue-green color of the planet in a small telescope. Comet C/2012 S1 (ISON) is the wildcard this month. As October begins, the comet remains stuck at 12th magnitude or fainter. It may brighten to 7th magnitude, easily bright enough for binoculars by month’s end, but so far the comet has been fainter than expected. On October 16, the comet will pass about 2º north of the bright star Regulus in the early morning sky, which will make it easy to find. It’s a busy month in the night sky…
1-15 October. The zodiacal light remains well placed for viewing in the eastern sky before sunrise in the northern hemisphere. This whitish glowing wedge of light appears to thrust out from the horizon. The zodiacal light is simply sunlight reflected off tiny dust particles in the inner solar system. For observers in the southern hemisphere, it’s best seen later this month and next in the western sky after sunset. Dark sky is essential.
3 Oct. Uranus reaches opposition, rising as the sun sets. This distant ice giant is found east of the Circlet of Pisces, and spends mid month moving within 0.3º of a 6th-magnitude orange star (see map below). In a telescope, look for the color contrast between the star and the pale blue-green glow of Uranus. Both are about the same brightness.
4 Oct. The star δ Geminorum (Wasat) will come within 6′ (that’s 1/10 of a degree) of the planet Jupiter. You’ll need sharp eyesight to distinguish between star and planet without optical aid. Binoculars or a telescope will give a good view, and it should make for an interesting astrophoto. You can’t miss this event… at magnitude -2.4, Jupiter is the brightest object in the early morning sky except for the Moon. It’s well above the eastern horizon by 2 a.m. and remains up until sunrise.
5 Oct. New Moon, 00:35 UT
8 Oct. The slender waxing crescent Moon passes close by Venus in the southwestern sky after sunset. Venus will brighten this month to magnitude -4.5. By month’s end, it will set nearly 2 hours after sunset. But it remains low above the southwestern horizon after sunset for northern observers. Stargazers in the southern hemisphere get a much better view of Venus after sunset, as well as the planets Mercury and Saturn and the bright red supergiant star Antares. By month’s end, the visible face of Venus is 50% illuminated.
11 Oct. First Quarter Moon, 23:02 UT
12 Oct. A rare triple shadow transit will occur on the face of Jupiter at 4:32 to 5:37 UT. The event will be visible from Europe and Africa and possibly eastern North America where the planet will be low over the eastern horizon. Use a telescope at moderate to high magnification to see the shadows of Io, Europa, and Callisto pass across the face of Jupiter. The planet reaches western quadrature today, 90º west of the Sun, which is an added bonus for casting striking shadows on the planet’s face.
15 Oct. Mars comes within 1º of the bright star Regulus in the constellation Leo in the pre-dawn sky above the eastern horizon. At magnitude 1.4, white Regulus is just a little brighter than red-orange Mars. Look for the striking color contrast between the two.
16 Oct. Comet ISON will pass about 2º north of the bright star Regulus in the early morning sky, then it will move within 1º of Mars from the 16th to the 18th. This is a good opportunity to scan for the comet with a small telescope.
18 Oct. Full Moon, 23:38 UT
23 Oct. Comet C/2012 S1 (ISON) reaches its greatest elongation from the Sun (about 55º). After today, it starts moving closer to the Sun as seen from Earth and will make its closest approach to the Sun on November 28, 2013.
26 Oct. Last Quarter Moon, 23:40 UT
26 Oct. Brilliant Jupiter comes close to the last-quarter Moon in the early hours of morning.
29 Oct. The waning crescent Moon, Mars, and Regulus form a tight triangle in the eastern pre-dawn sky.