On April 20, 2023, between 2:37 and 5:56 UTC, the moon passed between the sun and the earth. This produced a solar eclipse over the far northwest of Australia.
The plane of rotation of the moon around the earth and that of the earth around the sun are tilted by 5°. In order for the three stars to align, as in the top representation of the diagram, they must be in the same plane. That is to say on the axis of section of the two orbital planes. And for them to be aligned, it is necessary that the sun is on this axis of section. The lunar orbit rotating slowly, this happens every 173 days. So we could have an eclipse about twice a year.
The moon may not be in the right place in its orbit, so solar eclipses only occur somewhere on Earth about every one to two years. Not all of them are equal, however. Some pass over the ocean, others in areas that are often cloudy or barely visible above the horizon. In Australia, the one on April 20 was rare because it was total and visible, high on the horizon, from a semi-desert area. The earth passed through the cone of shadow as on marker A.
This eclipse is all the more remarkable because it was a hybrid eclipse. The earth-moon distance was just at the edge of the cone of darkness. So it went from an annular eclipse at first (a solar circle was visible around the moon as in marker C), then total (as in A) and again annular depending on where on the globe it was observed.
For the anecdote, the moon moves away from the earth very slowly, of 3,78cm per year. In a few hundred million years, there will be no more total eclipse, only annular ones.
Observation in Australia
The solar eclipse on the 20th of April was visible from Australia from 10:04, local time. This site shows the percentage of darkening, but also the chance of cloudiness, which is very low at this location. Three points seemed appropriate on the coast where there are fewer clouds:
- On the West of the Exmouth peninsula, the points 1 (eclipse at its maximum at 11h28:43, local time) and 2 (maximum eclipse at 11h28:48). The eclipse was total during 1:02 minutes.
- On the East, the point 3 (eclipse at its maximum at 11h29:58, local time). The sun was fully occulted for 1:03 minutes.
The next total solar eclipse over Australia will occur on the 13th of July 2037. It will be visible near Uluru. Enthusiasts please note!
Lunar eclipse 5-6 May
The moon revolves around the earth in just over 27 days. Half a revolution (about two weeks) before or after the solar eclipse, there is usually a new alignment of the stars. The moon then passes behind the earth which masks the light of the sun which illuminates our satellite. It is a lunar eclipse. It is not the same as the new moon, where we would see the unlit phase of the star. The moon is then illuminated with a pinkish-red hue.
For the solar eclipse of April the 20th, the lunar eclipse occured on the 6th of May over Australia, around 3 am local time. It was a penumbral eclipse: the moon was in the penumbral zone where the earth masked only part of the sunlight (position A on the following diagram). The next partial lunar eclipse took place on September 17 and we will have to wait until December 20, 2029 to see a total eclipse from Europe. But unlike the eclipse, it will be visible from the entire surface of the earth. More details on the site timeanddate.
