Ephemeris: 05/19/2026 – The Greeks discovered that the Earth was round and determined the Moon’s distance

May 19, 2026 Leave a comment

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

Partial Lunar Eclipse showing arc of the Earth's shadow
Partial Lunar Eclipse showing circular arc of the Earth’s shadow. Taken by me from the Veen Observatory of the Grand Rapids Amateur Astronomical Association at 04:15 UT August 17, 1970.
The partially eclipsed Moon setting through a thin cloud and the neighbor kid’s swing set.
The partially eclipsed Moon setting through a thin cloud and the neighbor kid’s swing set at 7:09 AM EDT April 4, 2015. Sunrise that morning was at 7:18 AM. Taken with a smartphone through 10X50 binoculars. If the Earth were pizza shaped, it would cast a shadow like the cloud in the image.
Earth and Moon size and distance to scale.
Earth and Moon size and distance to scale. Modified from the original GIF animation by the author.

Categories: Astronomical History, Ephemeris Program, The Earth, The Moon Tags:

Ephemeris: 05/18/2026 – Earth shines on the Moon

May 18, 2026 Leave a comment

This is Bob Moler with Ephemeris for Monday, May 18th. Today the Sun will be up for 14 hours and 56 minutes, setting at 9:07, and it will rise tomorrow at 6:10. The Moon, 2 days past new, will set at 12:07 tomorrow morning.

The Moon tonight will appear as a thin sliver, with Venus below and left of it. However, if as you look at the Moon closely tonight you may have the funny feeling that the whole moon is actually visible, you would be right. It’s easily confirmed with a pair of binoculars or a small telescope. What is illuminating the dark part of the Moon is earthshine. The Earth is big and bright in the Moon’s sky, as a fat waning gibbous orb from its vantage point. From the Moon the Earth has the opposite phase that we see of the Moon from the Earth. The effect used to be called by the term “Old moon in the new moon’s arms”. The effect was first explained by Leonardo da Vinci some 500 years ago. The effect will disappear in a few days as the Moon gets brighter and the Earth less so in the Moon’s sky. Earthshine will appear again when the Moon appears as a waning crescent in the morning. But not many of us are up to see it at that hour.

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

Earthshine by Bob Moler
Earthshine shown on a waxing crescent Moon taken by me back in the days before digital cameras. The bright crescent had to be overexposed to bring out the night side being illuminated by the Earth. The over exposure crescent part caused it to “bloom”, expanding it to adjacent parts of the image.
During the solar eclipse caused by the Moon, while Integrity and the crew were again in sight of the Earth, but not of the Sun, the Earth’s reflected sunlight illuminates the upper left part of the Moon. Credit: NASA/Artemis 2 crew.
The first solar eclipse experienced by the Artemis 2 crew, caused by the Earth. In this longer exposure, the night side of the earth is flooded by moonshine from the nearly full Moon in the Earth’s sky. What surprises is the color. On Earth the world appears in shades of gray under the light of the nearly full moon. The reason is the low light level. Our eyes have two kinds of photoreceptors: cones and rods. The cone s work best in bright light. They detect colors. Rods, work at low light levels, sacrificing color detection. Credit: NASA/Artemis 2 crew.

Categories: Artemis Program, Eclipses, Ephemeris Program Tags: ,

Ephemeris: 05/15/2026 – Orion flees the evening sky as Scorpius rises

May 15, 2026 Leave a comment

This is Ephemeris for Friday, May 15th. Today the Sun will be up for 14 hours and 49 minutes, setting at 9:04, and it will rise tomorrow at 6:13. The Moon, 1 day before new, will rise at 5:34 tomorrow morning.

Orion the winter constellation is just about gone from our spring skies. Only the top part of his club is left in the west as evening twilight fades. Rising in the southeast at the same time is his nemesis the constellation Scorpius the scorpion. According to Greek mythology, Orion was killed by a giant scorpion. And that scorpion of course was Scorpius. It was sent by the goddess of the earth Gaia. Orion, the mighty hunter, had boasted that he could kill any creature. So this was his final comeuppance. In that battle he was killed by the sting of that scorpion. And that is why Scorpius and Orion can never be in the sky at the same time. Orion won’t venture into the evening sky until Scorpius is long gone in late autumn.

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

Scorpius chasing Orion out of the evening sky. Two views of the horizon at 11 PM, with Scorpius rising in the southeast, while all that's left of Orion is upraised right forearm and club setting in the west.
Scorpius chasing Orion out of the evening sky. Two views of the horizon at 11 PM, with Scorpius rising in the southeast, while all that’s left of Orion is his upraised right forearm and club setting in the west. Created using Stellarium, LibreOffice Draw and GIMP.
Orion's fatal clash with the giant scorpion. A Google Gemini AI image created with the prompt: "A scene about the death of Orion the hunter by the sting of a giant scorpion of Greek myth. The scene: Orion, with sword in hand, preoccupied with the scorpion's claws, not noticing the scorpion's curved tail and stinger descending on him from above."
Orion’s fatal clash with the giant scorpion. A Google Gemini AI image created with the prompt: “A scene about the death of Orion the hunter by the sting of a giant scorpion of Greek myth. The scene: Orion, with sword in hand, preoccupied with the scorpion’s claws, not noticing the scorpion’s curved tail and stinger descending on him from above.”
Categories: Constellations, Ephemeris Program, Mythology, Observing Tags: ,

Ephemeris: 05/14/2026 – Looking at the bluest first magnitude star: Spica

May 14, 2026 Comments off

This is Bob Moler with Ephemeris for Thursday, May 14th. Today the Sun will be up for 14 hours and 47 minutes, setting at 9:03, and it will rise tomorrow at 6:14. The Moon, 2 days before new, will rise at 5:02 tomorrow morning.

In the south at 11 PM is the bright star Spica in Virgo the virgin. Arcturus, high in the southeast, is much brighter than Spica and has an orange tint to Spica’s bluish hue. In fact, Spica is the 15th brightest and the bluest of the 21 first magnitude stars. That means that it has a really hot surface temperature. I found that out once photographing a lunar eclipse near Spica, The star came out very blue, much bluer than seen visually. Spica is actually two stars in a tight 4-day orbit of each other. They are both reasonably matched in mass and brightness. The twin stars of Spica are 250 light years away. I’m glad the stars are young now. They will have a very interesting future as they age and interact in the next few million years.

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

Finding Spica
Spica finder animation for May evenings. First, follow the arc of the handle of the Big Dipper to find Arcturus. Then straighten it to a spike to find Spica. Click on the image to enlarge. Created using Stellarium and GIMP.
The binary stars that make up Spica in this artist’s depiction
The binary stars that make up Spica in this artist’s depiction. The stars cannot be separated in telescopes, but were detected by their Doppler signatures in the stars’ spectra as they orbit each other in 4 days..
Categories: Ephemeris Program, Observing, Stars Tags: ,

Ephemeris: 05/13/2026 – Where are the naked-eye planets this week?

May 13, 2026 Comments off

This is Ephemeris for Wednesday, May 13th. Today the Sun will be up for 14 hours and 45 minutes, setting at 9:02, and it will rise tomorrow at 6:15. The Moon, 3 days before new, will rise at 4:37 tomorrow morning.

Let’s take our weekly look at the whereabouts of the naked-eye planets. By 9:30 PM tonight, about a half hour after sunset, Venus may be seen in the western sky. A telescope will show a very tiny disc on Venus, because it is still pretty much beyond the Sun, 128 million miles (205 million kilometers) away from us. Over the next 5 months it will be moving closer to us and becoming much larger. Jupiter is the second-brightest star-like object in the western sky seen before 10 PM. It is above and left of the brighter Venus. Venus will set at 11:38 PM, while Jupiter will hold out until 1:21 AM. Saturn may be glimpsed just after it rises in the east at 4:48 AM, before morning twilight overwhelms it sometime later.

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

Jupiter, and Venus with a few remaining winter stars at 10 PM tonight, May 13, 2026. The planets are appearing to approach each other. They will be in conjunction on the evening of June 8th.
Jupiter, and Venus with a few remaining winter stars at 10 PM tonight, May 13, 2026. The planets are appearing to approach each other. They will be in conjunction on the evening of June 8th. Created using Stellarium.
The waning crescent Moon and Saturn at 5:15 AM May 14, 2026
The waning crescent Moon and Saturn at 5:15 AM May 14, 2026. Created using Stellarium.
A binocular or low power view of the waning creacent Moon showing the expected earthshine on its night side.
A binocular or low power view of the waning creacent Moon showing the expected earthshine on its night side. Created using Stellarium and GIMP.
Telescopic Venus, Jupiter and Saturn (north up) as they would be seen in a small telescope with the same magnification.
Telescopic Venus, Jupiter and Saturn (north up) as they would be seen in a small telescope with the same magnification, at the times indicated. Venus’ apparent diameter will be 12.2″, and be 84.7% illuminated. It’s on the far side of the Sun. Jupiter will be 34.4″ in diameter, with its moons shown for the time listed. The (”) symbol means seconds of arc, or 1/3600th of a degree. Created using Cartes du Ciel (Sky Charts), LibreOffice Draw and GIMP.
The naked-eye planets at sunset and sunrise on a single night, starting with sunset on the right on May 13, 2026. The night ends on the left with sunrise on the 14th.
The naked-eye planets at sunset and sunrise on a single night, starting with sunset on the right on May 13, 2026. The night ends on the left with sunrise on the 14th. Click or tap on the image to enlarge it. Created using my LookingUp app and GIMP.
A low precision ephemeris of the Sun Moon and naked eye planet positions for today and tomorrow, May 13 and 14th, 2026.
This is a low precision ephemeris of the Sun Moon and naked eye planet positions for today and tomorrow, May 13 and 14th, 2026. Some of the columns are self-explanatory, others are not. The transit column is the time that the body crosses the meridian and is due south. Elong, for elongation, is the angle between the Sun and that body. RA is right ascension, which is the object’s east-west position on the celestial sphere in hours and minutes. Dec is declination which is the north-south position of the object on the celestial sphere in degrees and minutes. R is the distance of that object from the Sun in astronomical units. An astronomical unit is about 93 million miles or 150 million kilometers. And Delta is the distance of that object from the Earth, also in astronomical units. I omit the ‘m’ in am and pm for compactness. The data was generated using my LookingUp for DOS app and displayed as a table by my Ephemeris Helper app.
Categories: Ephemeris Program, Naked-eye planets, Observing Tags: , , , , ,

Ephemeris: 05/12/2026 – Finding the constellations of Virgo and Libra

May 12, 2026 Comments off

This is Ephemeris for Tuesday, May 12th. Today the Sun will be up for 14 hours and 43 minutes, setting at 9:01, and it will rise tomorrow at 6:16. The Moon, 3 days past last quarter, will rise at 4:16 tomorrow morning.

As skies darken look to the south, below the bright star Arcturus, high in the southeast, and left and below Leo the lion, in the southwest, to the constellation of Virgo the virgin with its bright star Spica in the south. Other than Spica, Virgo contains only dim stars. It’s quite large, extending to the upper right, and to the left of Spica. Virgo represents two goddesses. The Greek harvest goddess Persephone, whose Roman name is Ceres, which is the root of our word cereal, is one. The bright star Spica is the ear of wheat that she’s holding in her hand. Some see her standing at an odd angle, I see her reclining. Virgo also represents Astraea the goddess of Justice, with her scales, the constellation Libra, at her feet low in the southeast.

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 Finder chart for the constellation Virgo the virgin in three frames.
A Finder chart for the constellation Virgo the virgin in three frames. Showing first just the stars as they would appear in the sky, then the constellation lines, and then the constellation art from Stellarium for Virgo and Libra. Created using Stellarium and GIMP.
Categories: Constellations, Ephemeris Program, Mythology, Observing Tags: ,

Ephemeris: 05/11/2026 – Finding the tiny but distinctive constellation of Corvus the crow

May 11, 2026 Comments off

This is Ephemeris for Monday, May 11th. Today the Sun will be up for 14 hours and 40 minutes, setting at 8:59, and it will rise tomorrow at 6:17. The Moon, 2 days past last quarter, will rise at 3:57 tomorrow morning.

The small constellation of Corvus the crow is located low in the south at 10:30 this evening. It’s made of 6 dim stars, but the pattern is a distinctive but distorted box with two stars at the upper left marking that corner, and another two marking the lower right corner. I usually don’t notice the extra star at these corners, which denote the wings of this crow in flight to the upper right. To me the box is distinctive enough. It’s pretty much alone below Virgo and its bright star Spica, left an above it. I don’t see a crow here, but the box is distinctive in that no two sides are parallel. In the US we call the shape a trapezium, the British call it a trapezoid. Anyway it is a very memorable shape, at least to me.

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

Corvus the crow finder for 10:30 PM, May 11, looking south.
Corvus the crow finder for 10:30 PM, May 11, showing just the stars, then constellation lines, and finally constellation art. I substituted Stellarium’s art for Corvus with my own, which I thought fit the stars better. Actually I don’t see a crow here. distinctive patern of its four brightest stars is enough. Created using Stellarium, LibreOffice Draw, GIMP and a flying crow inage found on the Internet.
Categories: Constellations, Ephemeris Program, Observing Tags:

Ephemeris: 05/08/2026 – The story of Boötes and Ursa Major

May 8, 2026 Comments off

This is Ephemeris for Friday, May 8th. Today the Sun will be up for 14 hours and 33 minutes, setting at 8:56, and it will rise tomorrow at 6:21. The Moon, 1 day before last quarter, will rise at 2:55 tomorrow morning.

Appearing in the eastern sky at 10 p.m. tonight is the kite shaped constellation of Boötes the herdsman. The bright star Arcturus is at the bottom of the kite which is horizontal to the left, pointed to by the arc of the handle of the Big Dipper, higher in the east. The Big Dipper is the hind end of the constellation Ursa Major, the Great Bear. In one story, Boötes represents a young hunter named Arcas, son of Callisto, a beautiful young woman who had the misfortune of being loved by god Zeus. Zeus’ wife, Hera, found out about the affair, and since she couldn’t punish Zeus, turned the poor woman into a bear. Arcas, many years later, unaware of why his mother disappeared, was about to kill the bear when Zeus intervened and placed them both in the sky, where he continues to chase her across the sky nightly.

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 GIF finder image for the constellations Boötes, Ursa Major, and Canes Venatici. It shows, in three frames: the sky as it would appear high in the east, the same image with constellation lines, and the art from the Stellariam app. See the caption for the image below for the inclusion of Canis Venatici.
A Google Gemini AI image created from a prompt I made which encapsulated the encounter of Arcas and the bear.
This is a Google Gemini AI image created from a prompt I made which encapsulated the encounter of Arcas and the bear in very sketchy terms. The source that it referenced turned out to be my April 26, 2019 Ephemeris post which is virtually identical to the one today. It was illustrated with a 17th century woodcut, which looked nothing like this image. I was kinda hoping it would have found another source, somewhere. I can’t be the only one. This is the second mythological image I requested from Gemini, and in both cases it created an image in the style of a renaissance painter. I noticed too that the bear has a look of recognition on its face. Gemini also included hunting dogs. Of course, Arcas would have had hunting dogs, and there is a constellation of the hunting dogs nearby. It’s just two stars, called Canes Venatici. I’ve ignored its part of the story all these years, so starting now I’m adding it in.
Categories: Constellations, Ephemeris Program, Mythology, Observing Tags: , , , , ,

Ephemeris: 05/07/2026 – A constellation of a real person: Coma Berenices

May 7, 2026 Comments off

This is Ephemeris for Thursday, May 7th. Today the Sun will be up for 14 hours and 30 minutes, setting at 8:55, and it will rise tomorrow at 6:22. The Moon, 2 days before last quarter, will rise at 2:28 tomorrow morning.

High in the south-southeast at 10:30 p.m. is a tiny and faint constellation of Coma Berenices, or Berenice’s Hair. In it are lots of faint stars arrayed to look like several strands of hair to the naked eye. The whole group will fit in the field of a pair of binoculars, which will also show many more stars. Berenice was a real queen, whose husband, the Pharaoh Ptolemy III, was away at war. Those were the days when the Greeks ruled Egypt. She offered her golden tresses to the gods for the king’s safe return. The hair, was placed in a temple. However, the offering disappeared when the king returned. Later, the constellation of Coma Berenices has been made to commemorate the queen’s sacrifice.

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 Coma Berenices finder. The Babylonians, who predated Queen Berenice, saw the cluster of stars as the tuft at the end of Leo the lion’s tail. The constellation, as we know it now was given by Tycho Brahe, the prominent 16th century observational astronomer. Created using Stellarium and LibreOffice Draw.
Coma Berenices cluster binocular view.
Approximate 7 power binocular field of view (FOV) of the Coma Berenices Cluster. Created using Cartes du Ciel (Sky Charts).

Categories: Constellations, Ephemeris Program, Mythology, Observing Tags:

Ephemeris: 05/06/2026 – Taking our weekly look at the whereabouts of the naked-eye planets

May 6, 2026 Comments off

This is Ephemeris for Wednesday, May 6th. Today the Sun will be up for 14 hours and 28 minutes, setting at 8:53, and it will rise tomorrow at 6:24. The Moon, 3 days before last quarter, will rise at 1:55 tomorrow morning.

Let’s take our weekly look at the whereabouts of the naked-eye planets. By 9:30 PM tonight or about 35 minutes or so after sunset, Venus may be seen very low in the West. A telescope will show a very tiny disc on Venus, because it is still pretty much beyond the Sun, 131 million miles (211 million kilometers) away from us. Over the next 5½ months it will be moving closer to us and becoming much larger. Jupiter is the brilliant star-like object in the western before 10 PM. It is above and left of the brighter Venus. Venus will set at 11:26 PM, while Jupiter will hold out until 1:40 AM. Saturn may be glimpsed starting about next Monday just after it rises in the east around 5:15 AM, and before morning twilight overwhelms it sometime later.

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

Jupiter, and Venus with fading winter stars at 10 PM tonight, May 6, 2026.
Jupiter, and Venus with fading winter stars at 10 PM tonight, May 6, 2026. Jupiter and Venus are appearing to approach each other. They will be in conjunction on the evening of June 8th. Created using Stellarium.
The Moon, 2 days before last quarter, as seen at 5 AM tomorrow morning, May 7, 2026. A view visible in small telescopes showing an image with and without selected features labeled. Created using Stellarium, LibreOffice Draw, and GIMP.
Telescopic Jupiter and Venus (north up) as they would be seen in a small telescope with the same magnification.
Telescopic Jupiter and Venus (north up) as they would be seen in a small telescope with the same magnification. Venus will be visible for a short time near the western horizon, while Jupiter will be visible until after midnight. Venus’ apparent diameter will be 11.9″, and be 86.5% illuminated. It’s on the far side of the Sun. Jupiter will be 35.0″ in diameter, with its moons shown here for 10 PM, tonight May 6, 2026. Callisto will begin to transit the face of Jupiter at 10:31 PM.. Europa will pass behind the planet (an occultation) beginning at 11:36 PM. The moons can shift noticably over an hour, especially Io and Europa. The (”) symbol means seconds of arc, or 1/3600th of a degree. Created using Cartes du Ciel (Sky Charts), LibreOffice Draw and GIMP.
The naked-eye planets at sunset and sunrise on a single night.
The naked-eye planets at sunset and sunrise on a single night, starting with sunset on the right on May 6, 2026. The night ends on the left with sunrise on the 7th. Click or tap on the image to enlarge it. Created using my LookingUp app and GIMP.
A low precision ephemeris of the Sun Moon and naked eye planet positions for today and tomorrow, May 6 and 7th, 2026.
This is a low precision ephemeris of the Sun Moon and naked eye planet positions for today and tomorrow, May 6 and 7th, 2026. Some of the columns are self-explanatory, others are not. The transit column is the time that the body crosses the meridian and is due south. Elong, for elongation, is the angle between the Sun and that body. RA is right ascension, which is the object’s east-west position on the celestial sphere in hours and minutes. Dec is declination which is the north-south position of the object on the celestial sphere in degrees and minutes. R is the distance of that object from the Sun in astronomical units. An astronomical unit is about 93 million miles or 150 million kilometers. And Delta is the distance of that object from the Earth, also in astronomical units. I omit the ‘m’ in am and pm for compactness. The data was generated using my LookingUp for DOS app and displayed as a table by my Ephemeris Helper app.

Categories: Ephemeris Program, Naked-eye planets, Observing Tags: , , , , ,