Skywatch Line for Wednesday and Thursday, October 1 and 2, 2025, written by Alan French

This is Dudley Observatory’s Skywatch Line for Wednesday and Thursday, October 1 and 2, 2025, written by Alan French.

The Sun rises at 6:53 A.M. on Wednesday and sets at 6:36 P.M. On Thursday it rises at 6:54 A.M. and sets at 6:34 P.M. Thursday lost 20 minutes,10 seconds of daylight compared to last Thursday.

The Moon was at first quarter on Monday and is now moving toward full. On Wednesday a waxing gibbous Moon rises at 4:03 P.M. toward the southeast.

At 7 P.M. on Wednesday a 69% sunlit Moon will lie 20 degrees above the south southeastern horizon. It will be due south and 23 degrees high at 8:35 P.M. and will set at 1:13 A.M. Thursday. The Moon’s low path across the southern sky keeps it in our skies for only 9 hours, 10 minutes on Wednesday night into Thursday morning.

Thursday’s Moon rises at 4:34 P.M. in the east southeast and its visible face will be 78% in sunlight. It will transit at 9:25 P.M. when it will be 28 degrees above the horizon. The Moon will set at 2:26 A.M. Friday.

Either night would be nice for observing the Moon with binocular or any spotting scope. Neither is well suited for looking high in the sky, so the Moon’s low altitude can be an advantage. Detail is most obvious along the terminator, now the sunrise line marching across the Moon’s surface. Here shadows are longest and detail stands out. Of course, these are also good nights for lunar observation with an astronomical telescope.

The Moon will reach full on Monday, October 6. The next new Moon is Tuesday, October 21.

Venus continues to be prominent in morning twilight. At 6 A.M. our sister planet, closely matching Earth in size, is 12 degrees above the eastern horizon and at magnitude -3.9. Its brilliant, small 11 arcsecond disk is nearly full and uninteresting through a telescope. At 10 P.M. EDT Wednesday it is at perihelion, its closest approach to the Sun, 107.47 million kilometers away. Venus is 226 million kilometers from Earth now.

None of the planets are in circular orbits, but Venus has the lowest eccentricity of any of them. Its distance from the Sun varies from its current close approach, 107.47 million kilometers (66.76 million miles) to aphelion, at 108.94 million kilometers (67.69 million miles). That is an eccentricity of only 0.0068. Our Earth’s eccentricity is 0.017.

Mercury, the innermost planet, with an eccentricity of 0.2056, has the highest eccentricity of any of the planets. At perihelion it is 46 million kilometers from the Sun, while at aphelion it is 70 million kilometers away. It receives twice as much solar radiation at perihelion as it gets at aphelion.