Planet watching is exciting this month as Jupiter and Saturn draw closer to each other for December’s great conjunction. Start watching them evenings just east of Sagittarius. Each planet is moving toward Capricornus. Jupiter is moving eastward faster than Saturn and will catch up to it a few days before the end of the year for the closest conjunction the two objects have had in almost four centuries. The moon will pass by the planets on the 22nd and 23rd. Also out there, between Jupiter and Saturn, is Pluto.
Mars is moving from between the fish in Pisces to alongside the southern fish. It’s at opposition on the 14th 0.42 astronomical units from Earth. That means it’s 42% of the distance from us as we are from the sun on average. Besides being closest to Earth at opposition, it’s opposite the sun. So when the sun sets, the red planet rises and stays up all night until the sun comes up again. It’s a great time to view Mars. If you can’t see Mars that night, don’t worry. The view will be almost as good all this month.
Venus starts the month in Leo and will have a conjunction just 0.1° from Regulus on the 2nd. The best viewing for this is going to be from about 50° to 90° east longitude. Viewers in western Asia and the western part of the Indian Ocean will get a splendid view of Venus one-fifth of a moon width from the bluish double star 79 light years away. Look eastward in the morning. Everyone who’s not in that region will see Venus a little farther from the star before or after the close call.
The moon passes by Venus on the 13th.
Mercury is an evening object in October. For northern hemisphere observers, it’s barely above the horizon in the west. Viewers near the equator and south of it will get a better view this month. The planet’s at greatest elongation 25.8° east of the sun on the 1st. From about 30° south, the planet sets about two hours after the sun on that date. A very thin crescent moon will be right of Mercury on the 17th.
There are two full moons this month. The first is on the 1st. People in cultures that celebrate Halloween will delight in the fact that the second is on the 31st. The phases between them are first quarter on the 9th, new on the 16th, and last quarter on the 23rd.
In addition to a second full moon, October has a second planet at opposition. Viewing that one won’t be as good as for Mars though. Uranus reaches opposition on the 31st. Since it’s just 3° north of the full moon, don’t expect to see this dim planet. At its brightest, Uranus is barely visible with the naked eye. You must have a dark sky and good eyesight to see it. Binoculars will help and, of course, a telescope is better. But for this opposition of Uranus, even if you find it in a telescope, the best view is a week before or after opposition. It’s about 18.8 astronomical units from us.
The moon is at apogee on the 3rd at 406,300 km or 252,500 miles. It’s at perigee on the 16th at 356,900 km or 221,800 miles. And it’s at apogee again on the 31st at 406,500 km or 252,600 miles.
The moon crosses the equator going north on the 2nd, reaches northern lunistice on the 9th, goes south of the equator on the 15th, reaches southern lunistice on the 22nd, and goes north of the equator again on the 29th.
Venus is at perihelion on the 30th. It’s about 0.7 earth-sun distances from the sun.