Skywatch Line for Monday and Tuesday, September 30, and October 1, 2024, written by Alan French

This is Dudley Observatory’s Skywatch Line for Monday and Tuesday, September 30, and October 1, 2024, written by Alan French.

The Sun rises at 6:52 A.M. on Monday and sets at 6:37 P.M. On Tuesday it rises at 6:53 and sets at 6:36. The sky is completely dark and free of any vestiges of evening twilight by 8:12 P.M.

The Moon was at last quarter, having completely three-quarters of its trip around Earth since last new Moon, last Tuesday, September 24, and is now headed toward new. If you are up before sunrise on Monday or Tuesday morning, you can spot a very old Moon in the eastern sky.

On Monday look for the Moon around 5:50. It will be due east, 12 degrees above the horizon, and a slender crescent, with a little less than 5% of the Moon’s surface in sunlight. As time passes the Moon will move higher, but morning twilight will increasingly brighten the eastern sky.

On Tuesday morning the Moon will not rise until 5:40 A.M. and will be a little less than 1½ degrees high by 5:50. By 6:00 it will be 3 degrees high and by 6:10 almost 5 degrees high. You will need an excellent view to the east for a chance to spot it at first. The situation will improve as it moves higher, but the eastern sky will also grow brighter. With the Moon only 1½% in sunlight, you might need binoculars to spot it if the skies are not completely clear or morning twilight interferes significantly.

The Moon will reach new Wednesday afternoon.

Mars and Jupiter continue to share the morning sky. At 5:00 A.M. Mars is 55 degrees above the southeastern horizon. It is now at magnitude +0.5 and appears reddish. Through a telescope it appears only 7.5 arcseconds across and detail is difficult to make out.

When Mars reaches opposition on January 15 next year it will be magnitude -1.4 and appear 14.6 arcseconds across. While this is considerably less than its maximum size at a close and favorable
opposition, when it can appear 25 arcseconds across, Mars will be high in our skies. When it is due south on January 15, it will be 72 degrees high. It will be 65 degrees or higher when it transits all of January.

At 5:00A.M. brilliant Jupiter, shining at magnitude -2.5, is 68 degrees above the south southeastern horizon, and to the right of and above Jupiter. Through a telescope Jupiter appears just over 42 arcseconds across and its two main dark bands, on either side of the equator, the North and South Equatorial Belts, can be seen a small telescope at about 60 power. The four brightest moons, Io, Europe, Ganymede, and Callisto, are easily visible, appearing as stars to the east and west of the planet. Their apparent positions change are they orbit the planet, and they can pass behind or in front of Jupiter. Many planetarium apps will show the positions of Jupiter’s four Galilean moons.