Archive
Ephemeris: 05/19/2026 – The Greeks discovered that the Earth was round and determined the Moon’s distance
This is Bob Moler with Ephemeris for Tuesday, May 19th. Today the Sun will be up for 14 hours and 58 minutes, setting at 9:08, and it will rise tomorrow at 6:09. The Moon, 3 days past new, will set at 1:01 tomorrow morning.
The Ancient Greeks used lunar eclipses to determine that Earth is a sphere, and worked on determining the distance to the Moon. From ancient times, the Greeks knew that an eclipse of the Moon was caused by the Earth’s shadow falling on the Moon. Since the Earth’s shadow was always circular, no matter where the Moon was in the sky during an eclipse, the Earth must be a sphere since that’s the only three-dimensional body that always casts a circular shadow. They also used the size of the Earth’s shadow to estimate the distance to the Moon. The lunar distance, on average, is 60.8 times the Earth’s radius away. The first estimates were about one third of that. Hipparchus in the 2nd century BC got much closer at 68 Earth radii.
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
Ephemeris: 04/27/2026 – Mare Orientale made a splash!
This is Ephemeris for Monday, April 27th. Today the Sun will be up for 14 hours and 4 minutes, setting at 8:42, and it will rise tomorrow at 6:37. The Moon, halfway from first quarter to full, will set at 5:06 tomorrow morning.
One of the pictures that the astronauts of Artemis 2 took of the far side of the moon was one that revealed chains of craters which appear to be emanating from the Sea on the edge of what we can see on the moon from the Earth, called Mare Orientale or the Eastern Sea. It was created by the impact of an asteroid onto the Moon’s surface, maybe 4 billion years ago, kicking out debris in all directions. Apparently the ejecta thrown out created chains of craters that appear to trace back to Orientale. They are most easily seen to the north and west of Orientale towards the terminator, the sunrise line, where the shadows are deeper. There’s probably chains of craters going in other directions, but they have no shadows.
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
Ephemeris: 04/24/2026 – Where did the lunar “seas” come from?
This is Bob Moler with Ephemeris for Arbor Day, Friday, April 24th. Today the Sun will be up for 13 hours and 55 minutes, setting at 8:39, and it will rise tomorrow at 6:41. The Moon, 1 day past first quarter, will set at 4:08 tomorrow morning.
The face of the Moon is a bit more than half uncovered from our point of view, with first quarter occurring yesterday. It shows the string of lunar seas, those gray areas on the Moon which lead to the terminator, the Moon’s sunrise line. There is a larger sea called the Ocean of Storms on the eastern side of the Moon, as we see it. Most were created about 3.8 to 3.9 billion years ago by asteroid strikes. The same collisions happened to the Earth, but plate tectonics destroyed the evidence. Not so on the Moon. Many planetary scientists think it was the result of the Late Heavy Bombardment, caused by the changing orbits of mainly Saturn, Uranus and Neptune disrupting the asteroids, and sending them careening through the solar system.
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
Ephemeris: 04/17/2026 – The Moon’s Far Side isn’t dark!
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
Ephemeris: 04/14/2026 – My virtual flight with the Artemis II crew
This is Ephemeris for Tuesday, April 14th. Today the Sun will be up for 13 hours and 26 minutes, setting at 8:26, and it will rise tomorrow at 6:58. The Moon, 3 days before new, will rise at 5:55 tomorrow morning.
I hadn’t enjoyable time last week Monday afternoon listening to Artemis 2 astronauts talking with the science team on Earth about what they were seeing Moon’s far side. I have the program called Virtual Moon Atlas which allows one to see the entire Moon with the phase and shadows. And I was able to rotate it and get the phase right so it appeared pretty much as it did to the astronauts. So I was able to follow along with their discussions of the far side features that they were seeing and photographing. I could zoom in to craters and features they were talking about, but nowhere near the detail they were seeing. So I consider it to be a really great time of, in essence, flying along with the astronauts.
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; EST, UT – 5 hours) unless stated otherwise. Times will be different for other locations.
Addendum
Ephemeris: 04/07/2026 – The Artemis II crew made amazing observations of the Moon’s Far Side
This post was made late due to some WordPress posting issues last night.
This is Ephemeris for Tuesday, April 7th. Today the Sun will be up for 13 hours and 5 minutes, setting at 8:18, and it will rise tomorrow at 7:10. The Moon, 3 days before last quarter, will rise at 2:33 tomorrow morning.
Yesterday evening the Artemis 2 crew flew over the far side of the moon. The moon to us has a waning gibbous phase. The far side is actually a waxing crescent, so most of the far side was in night. They might have gotten a good look at Mare Orientale, which is right on the edge of the moon that we see from Earth. It is a double-walled sea that looks like a bulls eye. Now they’re on their way back to the earth and will splash down in the Pacific Ocean later this week. Unlike Apollo 8 which orbited the moon, they will not be flying over any proposed landing sites. They flew over the moon’s equator while Artemis 4 will attempt to land near the moon’s South Pole. Besides, the Lunar Reconnaissance Orbiter has surveyed it much better than they could have.
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; EST, UT – 5 hours) unless stated otherwise. Times will be different for other locations.
Addendum
The script for the program seen above was written and recorded Sunday night April 5th before Artemis 2’s lunar flyby. This comment is made after the flyby on the late afternoon of April 6th. I speculated about Mare Orientale being something I wanted to have them investigate. And they did spend a great deal of time observing it, so we should expect some very nice photographs of it when they’re sent back. The image above is from the Lunar Reconnaissance Orbiter taken several years ago, at least. I find it a really cool feature.
Ephemeris: 01/26/2026 – Artemis, not just flags and footprints
This is Ephemeris for Monday, January 26th. Today the Sun will be up for 9 hours and 35 minutes, setting at 5:43, and it will rise tomorrow at 8:07. The Moon, 1 day past first quarter, will set at 3:10 tomorrow morning.
The current space race or I might say more properly, Moon race, is more than it was in the 1960s this race is not simply what is called a flag and footprints race get there first and go home. We already did that 57 years ago. But to set up permanent settlements on the moon to explore and extract the Moon’s resources like water. Water is not for export. Whatever water we find on the Moon would still be fairly scarce and probably rationed. There’s also an unknown amount of helium 3, which is a useful fuel for fusion reactors. Something we don’t have on the Earth, but would be the Holy Grail for clean energy production. We don’t know the Moon’s mineral potential, but whatever we find won’t have to be hauled up a quarter of a million miles from the Earth.
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; EST, UT – 5 hours) unless stated otherwise. Times will be different for other locations.
Addendum
Ephemeris: 10/06/2025 – Tonight’s full moon is the Harvest Moon!
This is Ephemeris for Monday, October 6th. Today the Sun will be up for 11 hours and 26 minutes, setting at 7:13, and it will rise tomorrow at 7:48. The Moon, at full today, will rise at 6:53 this evening.
Today’s full moon is the nearest full moon to the autumnal equinox which makes it the Harvest Moon. Normally, October’s full moon is called the Hunter’s Moon, so it can be both at the same time. The indigenous peoples of our area, the Anishinaabe, call it the Falling Leaves Moon and indeed this month the leaves will fall from deciduous trees, after giving us a couple of weeks of spectacular color. The exact time that the moon will be full will be 11:48 PM this evening. Therefore, the Moon is going to rise very close to sunset. As a matter of fact, it will rise 20 minutes before sunset, so it should be a very spectacular rising of an orangish moon which, this time of year, will remind one of a pumpkin.
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
Ephemeris: 09/08/2025 – Previewing the Harvest Moon Effect
This is Ephemeris for Monday, September 8th. Today the Sun will be up for 12 hours and 52 minutes, setting at 8:05, and it will rise tomorrow at 7:14. The Moon, 1 day past full, will rise at 8:30 this evening.
Last night’s full moon was not the Harvest Moon. We normally expect the Harvest Moon to come in September, but this year it does not because it is not the closest full moon to the autumnal equinox. The full moon of October 6th, this year, is the nearest full moon to the autumnal equinox. So it this month’s full moon is called the Corn Moon. But the effects of this full moon are the same as the Harvest Moon, in that the Moon rises only slightly later each evening for about a week or so. The Moon tonight will rise only 20 minutes later than it rose last night. The average day-to-day interval of moon rising is about 50 minutes. This earlier rising time had the effect of extending twilight which helped early farmers with an extra hour to gather in their crops.
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
Ephemeris: 08/29/2025 – Late August crescent Moon stays low in the western sky
This is Ephemeris for Friday, August 29th. Today the Sun will be up for 13 hours and 22 minutes, setting at 8:24, and it will rise tomorrow at 7:03. The Moon, 2 days before first quarter, will set at 10:48 this evening.
There’s an interesting feature that I’ve noticed about the Moon this time of year. When there’s a waxing crescent Moon in the evening, in late summer to early autumn, it’s seen pretty low in the southwestern sky after sunset. Tonight it’ll be two days before first quarter so it’ll be a fat crescent. However, when it’s seen after sunset, it will be very low in the southwestern sky. Contrast that for early risers, at this time of year the waning crescent Moon moves at a steep angle to the horizon, as do the planets now in the east. And of course the opposite is true for late winter and early spring moons. By the way, the Harvest Moon is in early October this year. The Harvest Moon is the nearest full moon to the autumnal equinox.
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
Bob Moler's Ephemeris Blog 