Observing | Bob Moler's Ephemeris Blog

Ephemeris: 09/19/25 – A different take on Cygnus the swan

September 19, 2025 bobmoler Comments off

This is Ephemeris for Friday, September 19th. Today the Sun will be up for 12 hours and 18 minutes, setting at 7:45, and it will rise tomorrow at 7:27. The Moon, 2 days before new, will rise at 6:06 tomorrow morning.

Yesterday I looked the star in the beak of the constellation of Cygnus the swan and the informal constellation or asterism made from most of its stars the Northern Cross. Cygnus is the official International Astronomical Union constellation name. However, the indigenous Anishinaabe people of our area had another bird in mind when seeing these stars, which are now fairly high in the east in the evening: Ajijaak, (pronounced a-ji-jock) a Sand Hill crane. While the swan is flying, neck outstretched to the south through the Milky Way, the crane is flying northward with its long legs trailing behind. The bright star Deneb is at his head. Where I live I see more cranes than swans these days and hear their creaking-door-like calls, and see a pair from time to time in a field south of where I live.

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

Within the Summer Triangle we see Cygnus swan, first as the Northern Cross then as the lines of Cygnus the swan, then the figure of the swan that comes with Stellarium then finally my poor rendition of Ajijaak the crane. — Looking within the area of the Summer Triangle we see Cygnus swan, first as the Northern Cross then as the lines of Cygnus the swan, then the figure of the swan that comes with Stellarium then finally my poor rendition of Ajijaak the crane. Click or tap on the image to enlarge it. Created using Stellarium and GIMP.

Categories: Anishinaabek Constellation, Ephemeris Program, Observing Tags: Ajijaak, Cygnus, Northern Cross

Ephemeris: 09/18/2025 – A fine example of different star colors

September 18, 2025 bobmoler Comments off

This is Bob Moler with Ephemeris for Thursday, September 18th. Today the Sun will be up for 12 hours and 21 minutes, setting at 7:47, and it will rise tomorrow at 7:26. The Moon, 3 days before new, will rise at 4:56 tomorrow morning.

Alberio is the name of the star that is in the head of the constellation of Cygnus the swan, which is almost overhead these evenings. It is also at the foot of the asterism or informal constellation of the Northern Cross. To the naked eye Alberio looks like a single star, however even in small telescopes its true nature is revealed. It’s a double star whose individual star colors are strikingly different Its brightest star is yellow, and the dimmer star is blue. While star colors are subtle, these two, due to their apparent closeness, make an obvious color contrast. Unlike what your interior decorator says: In stars, blue is hot, yellow, orange and red are cool. The two stars are too far apart to be considered a binary star system, but appear to move together in space. It is what is called an optical double, though they’re both around 430 light years away.

Addendum

Animated Alberio finder chart. Albireo is located in the head of Cygnus the swan, or at the base of the Northern Cross. Tagged stars are, beside Albireo, the stars of the Summer Triangle: Deneb, Vega and Altair plus the star at the junction of the upright and crosspiece of the cross, Sadr. Created using Stellarium, LibreOffice Draw and GIMP.

The Blue and Gold double star Albereo (Beta Cygni) — The Blue and Gold double star Alberio (Beta Cygni) is a favorite summer object for the color contrast of its component stars. Credit: Daniel Dall’Olmo.

Categories: Double star, Ephemeris Program, Observing Tags: Alberio, Cygnus

Ephemeris: 09/17/2025 – Taking a look at the whereabouts of the naked-eye planets

September 17, 2025 bobmoler Comments off

This is Ephemeris for Wednesday, September 17th. Today the Sun will be up for 12 hours and 24 minutes, setting at 7:49, and it will rise tomorrow at 7:25. The Moon, 3 days past last quarter, will rise at 3:44 tomorrow morning.

Let’s take our weekly look at the whereabouts of the naked-eye planets. Saturn now rises at 8:01 PM in the east. In a telescope Saturn sports a very thin ring, 2° from being edge on. Saturn has an axial tilt of about 27°, so it has seasons like the Earth and since its rings are over its equator, when they go edge on to the Sun, it is an equinox for it, which happened in May. Earth being close to the Sun and moving, see nearly the same thing. Now the ring angle for us will decrease to about a third of a degree by November 23rd before increasing. By 6 AM Jupiter will appear above the brighter Venus in the Eastern sky and among the stars of Gemini. Venus and Jupiter will have the waning crescent Moon between them tomorrow morning.

Addendum

*Saturn, low in the east, below and a bit right of the Great Square of Pegasus*, which stand on one corner. Created using Stellarium.

*Venus, the waning crescent Moon and Jupiter are visible in the east among the winter stars at 6:00 AM tomorrow morning, September 18, 2025. Saturn is low in the west. Created using Stellarium.*

The waning crescent Moon with earth shine. — *The waning crescent Moon with earth shine on the morning of September 18, 2025. Not much detail can be made out in binoculars otherwise.*

Telescopic Saturn, Jupiter and Venus (north up) as they would be seen in a small telescope with the same magnification. On the evening of the September 17th 2025, Saturn will be 19.4″ in diameter, but its rings, even being nearly edge on, should show up brighter than seen here, and extend to 45.3″. They are tilted 2.0° from being edge on. On the morning of September 19th 2025, Jupiter will be 35.7″ in diameter. Europa is eclipsed by Jupiter, Io will begin its transit the face of Jupiter at 5:44 AM and will be nearly impossible to spot against the planet. Venus’ apparent diameter will be 11.5″, and be 88.8% illuminated. It’s on the far side of the Sun. 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, starting with sunset on the right on September 17th, 2025. The night ends on the left with sunrise on the 18th. 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, September 17th and 18th, 2025. 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: 09/15/2025 – Last month to view the southern Milky Way from Michigan

September 15, 2025 bobmoler Comments off

Taking a closeup look at the top of the first image using the Stellarium app. I use that distinctive group of 5 stars in the south end of Scutum, which is a Milky Way filled area between Aquila, above, and Sagittarius. I don’t have a name for it. I wish it did, but it is quite a landmark, (or maybe I should say skymark) to find some of the deep sky objects farther north of Sagittarius. But there’s no bright stars to point away. The five-star group can be easily seen in binoculars. I’ve used that as a guide since I was a kid. Created using Stellarium, annotations using LibreOffice Draw, and GIMP. **Note the star cluster on the lower left is M25, not M24.**

This is Bob Moler with Ephemeris for Monday, September 15th. Today the Sun will be up for 12 hours and 30 minutes, setting at 7:52, and it will rise tomorrow at 7:23. The Moon, 1 day past last quarter, will rise at 1:14 tomorrow morning.

September is the second of the two months we get to see the southern part of the Milky Way in the evening sky. At 10 PM the asterism of the Teapot of the constellation Sagittarius is pouring its tea on the southwestern horizon. It is in that direction that we look to the center of the Milky Way. Unfortunately there are clouds of dust and gas between us and the center, so we cannot see it visually, though it can be seen by radio waves and other means. There are a host of objects visible in binoculars and small telescopes. One does not need a star map to be able to find them, just point a telescope at low power or binoculars in that direction and sweep around slowly. There are treasures of star clusters and nebulae to be found.

Addendum

Annotated Sagittarius photograph — Sagittarius in a short time exposure with added annotations. The “M” designations are objects in Charles Messier’s catalog created in the latter half of the 18th century. LSSC is the Large Sagittarius Star Cloud, SSSC is the Small Sagittarius Star Cloud. Credit Bob Moler.

In the image above the amount of detail of the stars is approximately that of a pair of binoculars. The various nebulae and star clusters are denoted with M numbers. These are some of the brightest, what we call deep sky objects, in the catalog by Charles Messier, who is looking for comets. He numbered them as he came across them. The brightest star cluster is M7, which Claudius Ptolemy recorded in the 2nd century CE. The brightest nebula is M8, the Lagoon Nebula out of which a star cluster is being formed. In binoculars, it looks like a short horizontal gash. Next in brightness is M17, a fuzzy spot in binoculars, but appears as a glowing check mark, or swimming swan in a telescope. M20, the Trifid Nebula, is the next brightest nebula in which dark dust lanes divide it into three lobes. M16, the Eagle Nebula is very dim. Most of the time I miss the nebulosity, but its embedded star cluster is quite easily seen. The rest of the Messier objects are star clusters or a star cloud. Of these M22 is a globular star cluster and one of the easiest of these clusters to resolve, though it might take a telescope of 150 mm (6″) diameter to do it.

Categories: Constellations, Milky Way, Nebulae, Observing, Star Clusters Tags: Sagittarius, Teapot

Ephemeris: 09/12/2025 – Cassiopeia through the year

September 12, 2025 bobmoler Comments off

This is Ephemeris for Friday, September 12th. Today the Sun will be up for 12 hours and 39 minutes, setting at 7:58, and it will rise tomorrow at 7:19. The Moon, 2 days before last quarter, will rise at 10:19 this evening.

The constellation of Cassiopeia the queen looks to most of us like the letter W. However, since it is circumpolar, that is it seems to move around the North Pole of the sky without setting. It represents to us with various orientations. When it’s seen now in the evening in the northeast, it kind of looks like a misshapen number 3. In early winter it would be nearly overhead and be the letter M, not the University of Michigan block letter M, but the angular University of Minnesota M. In early spring, it’s in the northwestern sky as the Greek capital letter sigma. And finally in early summer it’ll be low in the north and become the upright letter W. I’ll return to Cassiopeia and tell her story later this autumn.

The orientation of Cassiopeia, and also the Big and Little Dippers at 3 month intervals. It’s the same as 6 hour intervals on the same night. I’m cheating here by keeping the sky dark. Created using Stellarium, LibreOffice Draw, and GIMP.

Categories: Constellations, Ephemeris Program, Observing

Ephemeris: 09/11/2025 – Finding Pegasus the flying horse

September 11, 2025 bobmoler Comments off

This is Bob Moler with Ephemeris for Thursday, September 11th. Today the Sun will be up for 12 hours and 43 minutes, setting at 8:00, and it will rise tomorrow at 7:18. The Moon, 3 days before last quarter, will rise at 9:43 this evening.

While we’ve been watching the stars and constellations of summer and the Milky Way, the constellations of autumn have been sneaking up on us from the east. Low in the east at 9 PM is one of the greatest constellations of autumn, Pegasus the flying horse. Her body or at least the front part of it is a large square of stars called the Great Square of Pegasus. It is an almost perfect rectangle. However, as she’s rising, it’s standing on one corner. This year it is above and left of Saturn. From the upper star are her front legs, from the rightmost star her neck and head extend in the stars. And from the left star of the square are what might look like her hind legs but aren’t. Only half of her body is in the stars. It’s another constellation, Andromeda.

Addendum

The four stars of the Great Square of Pegasus can be seen in the east. This year they're above the planet Saturn. — As autumn approaches. the four stars the Great Square of Pegasus can be seen in the east. This year they’re above the planet Saturn. In mid autumn Pegasus will be high in the south flying upside down, apparently a very aerobatic flying horse. Her story belongs to the great star story of the autumn constellations, of which I’ve given my take on here. Created using Stellarium, LibreOffice Draw, and GIMP.

Categories: Constellations, Ephemeris Program, Observing Tags: Pegasus

Ephemeris: 09/10/2025 – Our weekly look at the naked-eye planets

September 10, 2025 bobmoler Comments off

This is Bob Moler with Ephemeris for Wednesday, September 10th. Today the Sun will be up for 12 hours and 46 minutes, setting at 8:02, and it will rise tomorrow at 7:17. The Moon, 3 days past full, will rise at 9:14 this evening.

Let’s take our weekly look at the whereabouts of the naked-eye planets. Saturn now rises at 8:30 PM in the east. In a telescope Saturn sports a very thin ring, 2¼° from being edge on. Saturn has an axial tilt of about 27°, so it has seasons like the Earth and since its rings are over its equator, when the go edge on to the Sun, it is an equinox for it, which happened in May. Earth being close to the Sun and moving, see nearly the same thing. Now the ring angle will decrease to about a third of a degree by November 23rd before increasing. By 6 AM Jupiter will appear above the brighter Venus in the eastern sky and among the stars of Gemini. Venus and Jupiter are joining the bright winter stars, a beautiful sight in the morning twilight.

Addendum

*Saturn and the Moon at 10 PM tonight, September 10, 2025. Created using Stellarium.*

*The Moon t*onight, September 10, 2025. A view visible in small telescopes showing an image with and without selected features labeled. Created using Stellarium, LibreOffice Draw, and GIMP.

*Venus and Jupiter are visible in the east among the winter stars at 6:00 AM tomorrow morning, September 11, 2025. Saturn is off in the west-southwest. Created using Stellarium and GIMP.*

Categories: Ephemeris Program, Naked-eye planets, Observing Tags: Jupiter, Mars, Mercury, Moon, Saturn, Venus

Ephemeris: 09/08/2025 – Previewing the Harvest Moon Effect

September 8, 2025 bobmoler Comments off

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.

Addendum

The full moons of late summer and early autumn show the harvest moon effect. The Harvest Moon itself is the nearest full moon to the autumnal equinox. This year’s full moon in September is farther from the autumnal equinox than the full moon in October so it gets the name Corn Moon, however the effect is the same. The moon’s path in the sky near the eastern horizon when the Moon is full, this time of year, is very low to the horizon. This causes the Moon to rise much less than the 50 minutes average gain in rising times. The opposite is true for the late winter and early spring full moons which rise each night at a much greater interval than average. Created using Cartes du Ciel, (Sky Charts).

Categories: Concepts, Observing, The Moon Tags: Autumnal equinox, Harvest moon effect

Ephemeris: 09/04/2025 – Venus, the Morning Star

September 4, 2025 bobmoler Comments off

This is Ephemeris for Thursday, September 4th. Today the Sun will be up for 13 hours and 4 minutes, setting at 8:13, and it will rise tomorrow at 7:10. The Moon, 3 days before full, will set at 4:19 tomorrow morning.

Venus graces our morning sky as the Morning Star. It is seen, this year, along with the planet Jupiter. They are the two brightest planets. The Greek and others of that part of the world, early on, thought the evening and morning appearances of Venus were two different planets. The Mayans of Pre-Columbian Central America were meticulous observers of Venus, as is seen in one of their surviving books, the Dresden Codex. A Venus cycle lasts 584 days, from first appearance in the morning sky, its heliacal rising, through its morning appearance, disappearance behind the Sun, through its evening appearance and disappearance to the next heliacal rising. Astronomers call that it’s synodic period. Five synodic periods equal almost exactly 8 years.

Addendum

The Venus Cycle as seen by the Mayans. In the gray part of the cycle Venus in unobservable due to being too close to the Sun in the sky.

Perspective view of Venus’ orbit in relation to the Earth, showing change in phase and size with position. When Venus is on the right side of the Sun, it is visible in the morning sky, on the left in the evening. The numbers represent Venus’ apparent size in seconds of arc. The image was found on the Internet, uncredited from a defunct website.

Categories: Concepts, Ephemeris Program, Observing Tags: Venus, Venus Cycle

Ephemeris: 09/03/2025 – Our weekly look at the naked-eye planets

September 3, 2025 bobmoler 2 comments

This is Ephemeris for Wednesday, September 3rd. Today the Sun will be up for 13 hours and 7 minutes, setting at 8:15, and it will rise tomorrow at 7:09. The Moon, 3 days past first quarter, will set at 3:04 tomorrow morning.

Let’s take our weekly look at the whereabouts of the naked-eye planets. The Red Planet Mars is too close to the direction of the Sun to spot. This is the curse of trying to view evening planets, which are near the direction of the Sun in late summer and early fall, for us at higher latitudes. Saturn now rises at 8:58 PM in the east. In a telescope Saturn sports a very thin ring, 2 ½° from being edge on. This angle will decrease to about a third of a degree by November 23rd before increasing. By 6 AM Saturn will be in the southwest. Jupiter will appear above the brighter Venus in the eastern sky and among the stars of Gemini. Venus and Jupiter are joining the bright winter stars, a beautiful sight in the morning twilight.