This is the Skywatch Line for Monday and Tuesday, December 3rd and 4th.
The Sun sets at 4:22 PM; night falls at 6:03. Dawn begins at 5:28 AM and ends with the Sun rising at 7:09.
Bright planets are becoming difficult to find. Saturn, in Sagittarius, shines with zero magnitude about 10º above the southwestern horizon, low enough to ruin views of its ring system. Saturn sets at 6:12 PM.
Aquarius harbors two planets. Mars shines also with zero magnitude and appears about 89% lit. It lies about 36º high in the southern sky. It is best observed at 5:57 PM and sets at 11:29 PM. The Martian surface is becoming quite littered with spacecraft. The recent INSIGHT lander joins Curiosity, and 5 other NASA spacecraft either orbiting or on the surface. This does not count space efforts by other nations and failed missions. In fact, not long ago, Mars was known for the difficulty for safely placing probes in or around Mars. Neptune is normally difficult to locate; it shines with 8th magnitude and appears a tiny 2 arc-seconds in size. However, on Monday and Tuesday nights, the blue-green planet lies within 2º of the Red Planet, within the same low power field in most telescopes. Neptune is best observed at 6:06 PM and sets at 11:41 PM.
Uranus, in Pisces, is brighter with 5th magnitude and a bit larger than Neptune. It is situated near the star Omicron Piscium. It is best observed at 8:53 PM and sets at 3:35 AM.
Comet 46P/Wirtanen is closing in on Earth. It is found in the constellation Fornax (the Furnace) and heading towards the constellation Eridanus. It will be closest to the sun on Dec 12th and closest to Earth on the 16th. Recent observations place it at 6th magnitude, visible through binoculars and telescopes. Finder charts are available from astronomical media.
The 27-day-old Moon rises at 4:04 AM on Tuesday in Libra. It glows with 5th magnitude and appears about 8% illuminated. Wednesday’s Moon is fainter and thinner about 3% lit and rises at 5:10 AM. Wednesday’s Moon is the last easily observed old Moon. Tuesday’s Moon is about 4º from Venus, which makes seeing a planet during daytime easy. Most binocular fields are about 5º in size; so, both fit the same field of view.
By 9 PM, the constellation Cetus (the Whale) is moderately high in our skies. Occasionally, the Skywatch Line mentions the variable star Algol, which varies its light about every 3 days. However, there is another star in our sky that takes much longer to vary its brightness – Mira. Mira is classified as a pulsating variable. While it was known to ancients, it took the Polish astronomer Hevelius to name it “Mira” – Latin for “Wonderful” in 1662. Most star catalogs call it Omicron Ceti, which is in Cetus. Mira is a binary, two stars orbiting each other. Mira is ancient, about 6 billion years old and about 220 light-years distant. It is the prototype of a class of between 6 to 7 thousand similar variable stars. Mira varies its light every 332 days. Maximum can be between 2nd and 4.9th magnitude; minimum can be between 8.6 and 10th magnitude. The star usually takes 100 days to brighten and twice as long to fade. Most of its light is in the infrared spectrum, but the star is easily seen in ordinary telescopes. In Ultraviolet telescopes, it sports a comet-like tail. The last maximum was December 29, 2017, so its current maximum is just about now and visible in amateur telescopes. Finder charts are available from astronomical media.