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Ephemeris: 06/23/2026 – How the Sun sizes up to other stars

June 23, 2026 Comments off

This is Ephemeris for Tuesday, June 23rd. Today the Sun will be up for 15 hours and 34 minutes, setting at 9:32, and it will rise tomorrow at 5:58. The Moon, 2 days past first quarter, will set at 2:13 tomorrow morning.

Stars big and small, where does the Sun rank? It depends on the criteria. As far as mass goes, it’s pretty much in the middle. One can’t get stars much more than 20 times the mass of the Sun stars or stars less than a 10th the mass of the sun. As far as brightness goes, there are stars 100,000 times brighter than the sun and stars hundreds of times dimmer. All the stars that you can see with the naked eye, with very few exceptions, are all brighter than the sun intrinsically. As far as size goes from the largest and smallest, the sun ranks near the bottom, in a range from 1,000% down to 15% the sun’s diameter. Don’t feel bad about the sun’s ranking. Stars like the sun in mass, which determines those other qualities, live long enough for life like us to evolve.

The astronomical event times given in this blog are for the Traverse City/Interlochen area of Michigan (Lat 44.7° N, Long 85.7° W; EDT, UT – 4 hours) unless stated otherwise. Times will be different for other locations.

Addendum

A comparison of stars on the large side of the sun. Showing the sizes in order: Sirius, Pollux, Arcturus and largest of all UY Scuti. (UY is a variable star designation. It lies in the direction of the constellation of Scutum (the Shield) located north of Sagittarius looking toward the inner part of our Milky Way Galaxy.
This is a comparison of stars on the large side of the sun. There are stars smaller than the sun, however. Red dwarfs, which are less massive than the sun have diameters of maybe 10 to 15% that of the sun. White dwarfs, which are the end state of stars like the sun, are earth size or about 100th the size of the sun. Supernova explosions of massive stars produce either neutron stars of maybe 30 miles or so in diameter, or black holes whose size maybe a dimensional sport but whose event horizon is maybe a few miles in diameter. When the sun runs out of hydrogen in its core in five or so billion years from now it will bloat up to the size of Arcturus or larger for a short period of time, before shrinking down into a white dwarf. From ar.inspiredpencil.com
Categories: Astronomical fact, Ephemeris Program Tags: , ,

Ephemeris: 04/17/2026 – The Moon’s Far Side isn’t dark!

April 17, 2026 Comments off

This is Bob Moler with Ephemeris for Friday, April 17th. Today the Sun will be up for 13 hours and 35 minutes, setting at 8:30, and it will rise tomorrow at 6:53. The Moon is new today, and won’t be visible.

When I hear discussions about the Artemis 2 missions, some people who ought to know better still refer to the far side of the moon as the dark side. Officially we have the two faces of the moon: the near side and the far side. I’ll even accept front side and back side. Until 1959 no one had ever seen the far side of the moon so it was dark, in the sense that we could not see it. Not dark because of the lack of light. I’ve been thinking about it. The far side sees more light from the sun, so maybe we should call it the bright side. It certainly has fewer maria or seas, those dark patches that we see on the near side of the Moon. There’s only one on the far side, it’s called the Moscow Sea since the Russian spotted first. Mare Orientale, subject of much study by the Artemis 2 crew, straddles the near side-far side line. It’s closer to the sun when it’s fully illuminated than the near side by about half a million miles, and it doesn’t suffer solar eclipses to darken it like the near side, being already in night, like it always is, at full moon.

The astronomical event times given in this blog are for the Traverse City/Interlochen area of Michigan (Lat 44.7° N, Long 85.7° W; EDT, UT – 4 hours) unless stated otherwise. Times will be different for other locations.

Addendum

Photograph of the crescent Earth setting behind the limb of the Moon by the Artemis 2 crew.
The far side may seem to be the dark side in this photograph of earthset by the Artemis 2 crew. It is as bright as the brightest parts of the near side. These are the crater filled highlands, so it is the exact same brightness as the highlands on the near side. And indeed in traveling to the Moon, when it was seen half near side and half far side, there was no difference in the brightness of the highlands between the two. So the moon is really dark gray in brightness, on average. It reflects something like 12% of the sunlight it receives, while the earth is more than twice that reflectance. Astronomers call that quantity albedo. So the Moon has an albedo of 12% while the Earth has an albedo of something like 29% on average. So the reason the full moon is so bright at night is due to lack of competition from something that’s actually much whiter. Credit: NASA/ESA/CSA -The Artemis 2 crew.
Categories: Astronomical fact, The Moon Tags: ,