Bob Moler's Ephemeris Blog

Ephemeris: 03/24/2026 – Visibility of the Moon’s features

March 24, 2026 bobmoler Comments off

This is Ephemeris for Tuesday, March 24th. Today the Sun will be up for 12 hours and 22 minutes, setting at 8:00, and it will rise tomorrow at 7:36. The Moon, 1 day before first quarter, will set at 3:31 tomorrow morning.

The Moon, tonight is just a day before first quarter. Its position in the sky is close to where the Sun will be around the 1st day of summer, so it’s quite high in the southwest as it gets dark. It’s a great time to view the Moon with the telescope, in that the moon isn’t too bright, and there are lots of craters showing up due to their shadows. The terminator nearly cuts the Moon in half. It is in this case, the sunrise line creeping across the surface. It is deep morning shadows that help delineate the features. Looking at the limb of the Moon, the curved edge, the craters are hard to spot, because they are under the midday sun, showing no shadows, which makes them very indistinct.

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 Moon, 1 day before first quarter, as seen at 9 PM tonight, March 25, 2026. A view visible in small telescopes showing an image with and without selected features labeled. Created using Stellarium, LibreOffice Draw, and GIMP.

Categories: Ephemeris Program, Observing Tags: Moon

Ephemeris: 03/23/2026 – Looking out beyond the spring stars

March 23, 2026 bobmoler Comments off

This is Ephemeris for Monday, March 23rd. Today the Sun will be up for 12 hours and 19 minutes, setting at 7:59, and it will rise tomorrow at 7:38. The Moon, 2 days before first quarter, will set at 2:23 tomorrow morning.

It is becoming more obvious as the Moon waxes, that there’s more bright stars in the south and southwestern part of the sky than there are in the southeastern sky. That’s because the Milky Way runs through the winter part of the sky. It’s not as bright as the Milky Way appears in the summer since we are looking away from the center of our Galaxy. The disk of our galaxy causes stars to congregate near that Milky band, whether we can see it well or not. That is the main reason the winter stars are so bright. In the southeast we are looking at the spring sky. Leo the lion and of course the Great Bear with the Big Dipper are there, but we are mostly looking outside the disk or galaxy to the universe beyond. So we’re looking through fewer nearby stars, so the spring sky seems somewhat lackluster compared to the crazy chaos of the winter sky.

Addendum

Comparing the skies of spring on the left, specifically 9:00 PM on March 23rd. Looking at the Milky Way and the stars that we could see in our Galaxy and a view of what’s on the outside. The little red ovals are galaxies. There are some blue ovals in there too, which are also galaxies, but more than one. They are interacting galaxies. Also visible, is the major galaxy cluster of spring on the far left, the Virgo cluster, a big mashup of galaxies. Notice that along the milky path there are hardly any galaxies. This is called the zone of avoidance. It isn’t that the galaxies avoid that area, but that the dust and gas in the galactic plane blocks light from the galaxies behind it. Created using Stellarium and GIMP.

Categories: Ephemeris Program, Galaxies, Milky Way, Seasonal skies

Ephemeris: 03/20/2026 – Spring begins today!

March 20, 2026 bobmoler Comments off

This is Ephemeris for Friday, March 20th. Today the Sun will be up for 12 hours and 9 minutes, setting at 7:55, and it will rise tomorrow at 7:43. The Moon, 2 days past new, will set at 10:21 this evening.

At 10:46 AM today the season of spring will begin. It may or may not feel it in our neck of the woods, but astronomically at that time the Sun will appear to cross a point in the sky called the vernal equinox. Equinox means equal night, when the Sun is up for 12 hours, and set for 12 hours. It does, if you don’t look too closely, and in the old days clocks weren’t that accurate anyway. The vernal equinox is the point in the sky where the Sun crosses the celestial equator, which is above the Earth’s equator heading north. The North Pole will begin 6 months of daylight, while the rest of the Northern Hemisphere will bask in more than 12 hours of sunlight a day. The reverse is true in the Southern Hemisphere where autumn will start.

Addendum

The Sun's path through the apparent dome of the sky on an equinox day from the Traverse City/Interlochen area in Michigan — The Sun’s path through the apparent dome of the sky on an equinox day from the Traverse City/Interlochen area in Michigan. The Sun rises due east and sets due west. The Sun is plotted every 15 minutes. This is a stereographic projection which compresses the image near the zenith and enlarges the image towards the horizon. The blue azimuth and altitude marks are 15 degrees apart. Created using my LookingUp program and GIMP.

The Earth's axis points in the same direction as it orbits the Sun, causing the seasons. — The Earth’s axis points in the same direction as it orbits the Sun, causing the seasons. Credit: Timeanddate.com.

Categories: Ephemeris Program, Equinox Tags: March equinox, Spring, Vernal Equinox

Ephemeris: 03/19/2026 – Anticipating the beginning of spring

March 19, 2026 bobmoler Comments off

See Aurora alert below

This is Ephemeris for Thursday, March 19th. Today the Sun will be up for 12 hours and 6 minutes, setting at 7:54, and it will rise tomorrow at 7:45. The Moon, 1 day past new, will set at 9:02 this evening.

This is the last full day of winter. It seems strange that we know so accurately when the seasons begin and end astronomically, but never know what the weather’s going to do tomorrow with that same accuracy. The main reason is the number of variables involved. With the solar system, the earth and the sun in particular. There are very few variables. For instance, the masses of the Earth and the Sun, they’re distance apart and the gravitational constant, will give you a very close approximation. For the weather, there are tons of variables, plus what a butterfly did in Alaska last October. Knowing the date of the vernal equinox the first day of spring was and is important for agriculture, knowing when the world will warm up again.

Addendum

The first flowers in my yard are these guys that are the first to bloom after the snow melts. They appear to be Glory-of-the-Snow according to Google. — The first flowers in my yard are these little guys that are the first to bloom after the snow melts. They appear to be Glory-of-the-Snow according to Google. They have the long thin leaves. This was taken on April 5th, five years ago. I’m not sure if they will be as early this year, since we had the biggest snow storm of the season a few days ago, and we’re still digging out!

Aurora Alert

According to Spaceweather.com the Earth will be hit with 2 CMEs (Coronal Mass Ejections) from the Sun on the 19th and 21st respectively. See also NOAA’s Space Weather Prediction Center.

Categories: Ephemeris Program, Seasons

Ephemeris: 03/18/2026 – Taking our weekly look at the whereabouts of the naked-eye planets

March 18, 2026 bobmoler Comments off

This is Ephemeris for Wednesday, March 18th. Today the Sun will be up for 12 hours and 3 minutes, setting at 7:52, and it will rise tomorrow at 7:47. The Moon is new today, and won’t be visible.

Let’s take our weekly look at the whereabouts of the naked-eye planets. By 8:30 PM or about a half hour or so after sunset, Venus may be seen very low in the West. Binoculars or a telescope will show a very tiny disc on Venus, because it is pretty much behind the Sun, a good way from us. However over the next 7 months it will be moving closer to us and becoming much larger. Jupiter is the brilliant star-like object more than halfway up in the southern sky at 9 PM. It’s the brightest object in the sky at that point. It has resumed its normal eastward motion, spending most of its evening appearance making up the ground it lost in its 4 months of retrograde motion. The planet and its moons are a treat for binoculars or a telescope.

Addendum

Venus is seen low in the western sky at 8:30 PM tonight. — *Venus is seen low in the western sky at 8:30 PM tonight March 18, 2026, or 38 minutes after sunset. Created using Stellarium.*

Jupiter is seen with the bright winter stars in the south at 9:00 PM tonight. — *Jupiter is seen with the bright winter stars in the south at 9:00 PM tonight, March 18, 2026. Also showing are the zodiacal constellations of Taurus, Gemini, Cancer and Leo. Created using Stellarium.*

Telescopic Jupiter and Venus 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 is visible mopst of the night. Venus’ apparent diameter will be 10.4″, and be 95.7% illuminated. It’s on the far side of the Sun, 1.6 times the Sun’s distance from us. Jupiter will be 40.5″ in diameter, with its moons shown here for 9 PM, tonight March 18th, 2026. The moons can shift noticably over an hour. . 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 and the Moon at sunset and sunrise on a single night. — The naked-eye planets and the Moon at sunset and sunrise on a single night, starting with sunset on the right on March 18th, 2026. The night ends on the left with sunrise on the 19th. 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. — This is a low precision ephemeris of the Sun Moon and naked eye planet positions for today and tomorrow, March 18th and 19th, 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: Jupiter, Mars, Mercury, Moon, Saturn, Venus

Ephemeris: 03/17/2026 – It’s also an equilux day

March 17, 2026 bobmoler Comments off

This is Bob Moler with Ephemeris for St. Patrick’s Day, Tuesday, March 17th. Today the Sun will be up for 12 hours and to the minute, setting at 7:51, and it will rise tomorrow at 7:49. The Moon, 1 day before new, will rise at 7:33 tomorrow morning. | This upcoming Saturday will be the vernal equinox, the first day of spring. Equinox means equal night, meaning that day and night are equal. Geometrically that’s correct, but, that’s not actually true. Today is the day when the sun is up for 12 hours and of course set for 12 hours. The name for this day has come to be called equilux day. Lux being the Latin for light. The difference is, because the Earth has an atmosphere, plus we have a different definition of sunrise and sunset that puts the sun a little bit below the horizon at the rise and set moment. So enjoy a few extra minutes of sunlight before the official equinox date. Think of it as a St Patrick’s Day bonus.

Addendum

Atmospheric Refraction — How the atmosphere bends the light of the Sun or Moon rising or setting to appear higher than it actually is. S is the actual position of the Sun, S’ is the apparent position of the Sun. The blue line is the observer O’s horizon extended into space. The gray line is the actual, though much exaggerated, light path bent or refracted by the Earth’s atmosphere. The black line is the apparent sight line to the Sun. Credit Francisco Javier Blanco González, 2017.

A note: This is equilux day for folks a 45 degrees north latitude. The actual date may vary by a day or so depending on one’s latitude, which affects the angle the Sun appears to cross the horizon.

Categories: Astronomical Event, Concepts, Ephemeris Program Tags: Equilux, Equinox

Ephemeris: 03/16/2026 – The Big Dipper as seen from other places

March 16, 2026 bobmoler Comments off

This is Ephemeris for Monday, March 16th. Today the Sun will be up for 11 hours and 57 minutes, setting at 7:50, and it will rise tomorrow at 7:51. The Moon, 2 days before new, will rise at 7:14 tomorrow morning.

The Big Dipper is ascending in the northeastern sky this evening when it gets dark, it’s seven stars shining brightly. The Big Dipper is not an actual constellation, recognized internationally. It’s part, the hind part, of Ursa Major, the great bear. The Big Dipper is an asterism or informal constellation. It is a distinctly North American constellation. For fugitive slaves, fleeing the southern states in the days before the Civil War, the Drinking Gourd, as they called it, showed the direction north to freedom. In England the dipper stars become the Plough (plow), or Charles’ Wain (Charlemagne’s Wagon). In France, known for culinary delights it is the saucepan, or the cleaver. Many cultures saw what was familiar to them in these seven bright stars.

Addendum

Big Dipper as seen by different cultures — Cultural views of the Big Dipper as an Animation: Big Dipper/Sauce Pan, Plough (plow), Charle’s Wain (Charlemagne’s wagon), Cleaver.

Categories: Asterism, Ephemeris Program

Ephemeris: 03/13/2026 – Precession of the equinoxes

March 13, 2026 bobmoler Comments off

This is Ephemeris for Friday, March 13th. Today the Sun will be up for 11 hours and 47 minutes, setting at 7:46, and it will rise tomorrow at 7:56. The Moon, 2 days past last quarter, will rise at 6:01 tomorrow morning.

Yesterday I talked about the fact that the constellation of Cancer the crab is no longer the northernmost constellation of the zodiac, where the Sun is positioned on the first day of summer. There’s been a slow change in the position of the earth’s axis, in that it wobbles slowly in a period of nearly 26,000 years. The inclination of the Earth’s axis to its orbit is around 23 1/2 degrees, and the gravitational pull of the Moon and the Sun on the Earth’s equatorial bulge, wants to straighten it up. But because the Earth is spinning, it wobbles instead, slowly sliding the actual zodiacal constellations eastward about one constellation in 2,150 years. So the actual constellations are off one constellation from the astrological signs.

Addendum

An animation of the precession of the equinoxes. The blue horizontal line is the celestial equator. The orange line is the ecliptic, the apparent annual path of the Sun against the stars. Where the two lines cross is the vernal equinox where the Sun is on the first day of spring, which on our calendar is trending to be March 20th. The slippage of the stars eastward (to the left) along the ecliptic is about the apparent width of the Sun or Moon, or half a degree, in 36 years. We’re looking at two different years 150 CE, the time of Ptolemy, and our time. To tell which is which, the one from our time has Saturn at the lower right. Jupiter happens to be in both of them, but it’s obviously been around lots of times between then and now. Created using Stellarium and GIMP.

The force causing precession — The Moon and Sun’s gravitational force act on the Earth’s equatorial bulge attempting to cause the earth to straighten up and fly right. Because the Earth is spinning, it acts like a gyroscope and the torque to straighten it up causes it to be applied 90 degrees away in the direction of the rotation causing the procession. Credit: Open Course: Astronomy.

Precession circle — The path of the north pole of the sky (celestial sphere) over time. The celestial north pole is still approaching Polaris. In the past the Big Dipper was closer to the north pole of the sky than it is now. Polaris will be it closest to the north pole around the year 2110. Source: taichifuture.com/cosmology.html.

Categories: Concepts, Zodiac Tags: Precession

Ephemeris: 03/12/2026 – Cancer the crab used to welcome summer

March 12, 2026 bobmoler Comments off

This is Ephemeris for Thursday, March 12th. Today the Sun will be up for 11 hours and 44 minutes, setting at 7:45, and it will rise tomorrow at 7:58. The Moon, 1 day past last quarter, will rise at 5:25 tomorrow morning.

There’s a line on some globes and maps at approximately 23 1/2° north latitude called the Tropic of Cancer. It’s related to the constellation Cancer the crab. However, Cancer no longer fits that role that it was named to a couple of thousand years ago, when the sun entered the constellation of Cancer on the first day of summer. That’s the latitude on the Earth where the Sun was directly overhead on the first day of summer. Now that an honor goes to Gemini. The way we draw the figure of that constellation, the Sun is right near Castor’s big toe on the first day of summer. But I don’t think they’re going to change the name anytime soon. The reason for the change is that the Earth’s axis slowly wobbles like a top or gyroscope as they slow down. The effect is called precession.

Addendum

Comparison of the position of the Sun against the constellations on the summer solstice from 150 CE to now due to the precession of the equinoxes. The reason I chose 150 CE, is that it was the approximate date of Ptolemy’s Almagast, the standard work on astronomy until Copernicus in the 16th century or later. Created using Stellarium, LibreOffice Draw and GIMP.

*How the tropics of Cancer and Capricorn line up with the Sun on the solstices. From an animation in Wikipedia, in the Public Domain.*

The Greek letter epsilon in the image above represents the tilt of the Earth’s axis of around 23.5°. Astronomers call it the obliquity of the ecliptic, the angle between the ecliptic and the celestial equator as seen in the illustration below.

Precesion animation — The 25,700-year cycle of precession as seen from near the Earth. The current North Pole star is Polaris (top). In about 8,000 years it will be the bright star Deneb (left), and in about 12,000 years, Vega (left center). The Earth’s rotation is not depicted to scale – in this span of time, it would actually rotate over 9 million times. Credit image Tfrooo, caption Wikipedia.

Categories: Concepts, Constellations, Ephemeris Program, Seasons, Uncategorized Tags: Tropic of Cancer

Ephemeris: 03/11/2026 – Taking our weekly look at the whereabouts of the naked-eye planets

March 11, 2026 bobmoler Comments off

This is Ephemeris for Wednesday, March 11th. Today the Sun will be up for 11 hours and 41 minutes, setting at 7:43, and it will rise tomorrow at 8:00. The Moon, at last quarter today, will rise at 4:42 tomorrow morning.

Let’s take our weekly look at the whereabouts of the naked-eye planets. At 8:15 PM or about a half hour after sunset, Venus may be seen very low in the West. A very low western horizon will be necessary to spot it, like from the shore of Lake Michigan. Saturn is no longer visible, being too close to the direction of the Sun. Jupiter is the brilliant star-like object more than halfway up in the southern sky. It’s the brightest star-like object in the sky. The planet and its moons are a treat for binoculars or a telescope. Jupiter’s four brightest, so-called Galilean Moons are on the east side of the planet, though binoculars will probably show three. The moon closest to the planet are two moons close together, which are resolved in telescopes.