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07/28/2022 – Ephemeris – Why don’t we have solar eclipses every new moon?

July 28, 2022

This is Bob Moler with Ephemeris for Thursday, July 28th. Today the Sun will be up for 14 hours and 48 minutes, setting at 9:13, and it will rise tomorrow at 6:25. The Moon is new today, and won’t be visible.

The actual time when the moon is New will be 1:55 pm. The Moon will not eclipse the Sun this time. Why? Because the Moon is nearly 5 degrees, or 10 moon-diameters, north of the Sun. If the Moon orbited the Earth nearly in the same plane that the Earth orbited the Sun, we could have solar eclipses for somewhere on the Earth every new moon. As it is, the Moon orbits the Earth with about a 5-degree tilt to the Earth’s orbit of the Sun. So we get eclipse opportunities of eclipses about one in six new moons for solar eclipse and about the same for full moons and lunar eclipses. Of course, one has to be at the proper location to see them. If the Moon orbited the Earth over the Earth’s equator, like many other moons of other planets, eclipses would be much more rare and only occur around the equinoxes.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hours). They may be different for your location.

Addendum

The Sun and Moon at New Moon 7/28/2022

The Sun and Moon at New Moon at 1:55 pm today, seen as if the Earth had no atmosphere and one could see the Sun and stars at the same time. The orange line is the path of the Sun in the sky, called the ecliptic. The red line is the orbit of the Moon. Created using Stellarium.

Sun and Moon's orbits on the celestial sphere

Earth centered (geocentric) diagram of the heavens called the celestial sphere, showing the apparent orbits of the Sun and Moon. The Moon’s orbit has about a 5-degree tilt (exaggerated here) to the Sun’s apparent orbit, which we call the ecliptic. Solar eclipses occur when the new moon and Sun are near a node. Lunar eclipses occur when the full moon and Sun are near opposite nodes. My diagram.

The orbit of the Moon precesses, so the line of the nodes regresses, that is slowly rotating clockwise, backwards to the motion of the Sun and Moon (and all the rest of the planets), one rotation in 18.6 years.

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