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Ephemeris: 07/21/2025 – When our knowledge of the size of the universe expanded
This is Ephemeris for Monday, July 21st. Today the Sun will be up for 15 hours and 2 minutes, setting at 9:20, and it will rise tomorrow at 6:18. The Moon, 3 days before new, will rise at 3:18 tomorrow morning.
A little over 100 years ago astronomers the Milky Way and the surrounding stars were thought to be the entire universe. A universe which was, apparently, disc shaped. Astronomers photographed examples of objects they called spiral nebulae, which they thought belonged to the Milky Way. Then Edwin Hubble photographed stars in the Andromeda spiral nebula. One star changed brightness in a way like some of the stars we know in our Milky Way. These stars are called Cepheid Variables and the rate of variation in brightness is related to their true brightness. This star that Hubble found was much too dim and much too far away to be in the confines of the Milky Way. Soon we found that we are in a spiral nebula or galaxy, like billions of others.
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
Left: Carnegie Observatories. Right: NASA, ESA, and the Hubble Heritage Team (STScI/AURA); Acknowledgment: R. Gendler
The universe “expanded” again, when astronomers found out there were two types of Cepheids, one 4 times brighter than the other. Using the brighter Type I Cepheids, the measurement doubled the estimated distance*. This was about the time in the early 1950s when I was getting interested in astronomy, so the quoted distance to Andromeda and all the other galaxies doubled from older astronomy books to the newer ones.
* Inverse square law: brightness drops with the square of the distance. Double the distance and the brightness drops by 22 or 4.
Ephemeris: 09/30/2024 – Andromeda’s treasure, its great galaxy
This is Bob Moler with Ephemeris for Monday, September 30th. Today the Sun will be up for 11 hours and 43 minutes, setting at 7:24, and it will rise tomorrow at 7:41. The Moon, 2 days before new, will rise at 6:27 tomorrow morning. | For at least the last thousand or so years a fuzzy spot in the constellation of Andromeda has been known. It was known as the Great Andromeda Nebula until about 100 years ago. Nebula means cloud, and it belonged to the Milky Way. At that time it was finally recognized as another Milky Way just like ours. So the word to call it was galaxy, a word that means Milky Way. It looks to be among the stars of Andromeda, but it’s far beyond the stars that we make of the constellation Andromeda. Current estimates place it at about two and a half million light years away, well beyond the stars that we see in Andromeda that range to only a few thousand light years distance. It will collide with our galaxy in about 4 billion years.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hours). Times will be different for other locations.
Addendum
Ephemeris: 11/09/2023 – The Milky Way will collide with the Great Andromeda Galaxy
This is Bob Moler with Ephemeris for Thursday, November 9th. Today the Sun will be up for 9 hours and 49 minutes, setting at 5:21, and it will rise tomorrow at 7:32. The Moon, halfway from last quarter to new, will rise at 4:31 tomorrow morning.
Stars are at extreme distances compared to their sizes, even if one includes their planetary systems. Galaxies in a galaxy cluster are much closer with respect to their size. Astronomers have determined that our Milky Way galaxy will collide with the Great Andromeda Galaxy, some two and a half million light years away, in about four and a half billion years. Don’t worry, it is very unlikely that any stars will collide during the event, though the solar system may be in for a wild ride. As the galaxies approach each other their beautiful spiral structures will begin to distort into tidal tails. Multiple passes of the two will occur before they will coalesce into one large elliptical galaxy. Other galaxies of the Local Group will join in over time.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT –5 hours). They may be different for your location.
Addendum
Ephemeris: 11/07/2023 – How to find the Great Andromeda Galaxy
This is Ephemeris for Election Day for some, Tuesday, November 7th. Today the Sun will be up for 9 hours and 55 minutes, setting at 5:23, and it will rise tomorrow at 7:30. The Moon, 2 days past last quarter, will rise at 2:22 tomorrow morning.
The closest large galaxy to our Milky Way galaxy is the Great Andromeda Galaxy, seen high in the eastern sky when it gets dark. It is barely visible to the naked eye. To locate it, first find a large square of stars high in the east-southeast standing on one corner, the Great Square of Pegasus. The left star of the square is the head of the constellation Andromeda. Follow two stars to the left and a bit downward, then two stars straight up. The galaxy is near that last star as a small smudge of light. Binoculars are the best way to see it as a thin spindle of light. Using a telescope, one can see, besides its nucleus, its two satellite galaxies.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT –5 hours). They may be different for your location.
Addendum
10/18/2022 – Ephemeris – The Great Andromeda Galaxy
Oct 18. This is Bob Moler with Ephemeris for Tuesday, October 18th. Today the Sun will be up for 10 hours and 50 minutes, setting at 6:52, and it will rise tomorrow at 8:03. The Moon, 1 day past last quarter, will rise at 1:22 tomorrow morning.
The closest large galaxy to our Milky Way galaxy is the Great Andromeda Galaxy, seen in the eastern sky when it gets dark. It is barely visible to the naked eye. To locate it, first find the Great Square of Pegasus high in the east, standing on one corner. The left star of the square is the head of the constellation Andromeda. Follow two stars to the left and a bit downward, then two stars straight up. The galaxy is near that last star as a small smudge of light. Binoculars are the best way to see it as a thin spindle of light. Visually through a telescope, one can see only the bright nucleus of the galaxy, that spans six Moon diameters in photographs. M 31* is its most well known catalog designation, and it’s two and a half million light years away.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hours). They may be different for your location.
* M 31 is the 31st entry in French comet hunter Charles Messier’s catalog of fuzzy objects that can be mistaken for comets because they didn’t move in relation to the stars. It is a catalog of some of the brightest, what we call, deep sky objects: star clusters, nebulae, and galaxies. It is not a comprehensive catalog of these objects, since Messier was interested in comets.
Addendum
Andromeda animated finder, including the Great Andromeda Galaxy. I’ve added Cassiopeia that some folks use to find the galaxy. I start with the leftmost star of the Great Square of Pegasus that connects to Andromeda. I count off two stars on the lower curve because they are brighter than the upper curve. Then count two stars up. Next to that top star is a little smudge. That is the core of the Great Andromeda Galaxy. Click on the image to enlarge to full size. Created using Stellarium and GIMP.
Low resolution and exposure view of M 31, the Great Andromeda Galaxy, simulating what it looks like in binoculars. Credit mine.
M 31, The Great Andromeda Galaxy. This image really shows the red H II Regions intermixed with the dark dust lanes that delineate the galaxy’s spiral arms. H II or ionized hydrogen regions are illuminated by hot young stars that were born within them. Click on the image to enlarge it. Credit: Dan Dall’Olmo.
The moon superimposed on the Great Andromeda Galaxy, M31, for apparent size comparison. Created using Stellarium and the embedded image of the galaxy with that of the full Moon of October 31, 2020. M31 Image credit: Herm Perez: http://home.att.net/~hermperez/default.htm License: “Feel free to use these images, if you use them in a commercial setting please attribute the source.”
The Great Andromeda Galaxy is shown with two of its satellite galaxies, both elliptical. The nearly spherical one is M 32. The other one I knew and observed, in the 1950s, as NGC 205**. Even though Messier had described this object in 1773, he didn’t add it to his catalog. The suggestion that it be added as the last entry in Messier’s catalog was made in 1967 by Welsh amateur astronomer Kenneth Glyn Jones***
** NGC is the New General Catalogue of Nebulae and Clusters of Stars, and is not so new. It was published in 1888 by John Louis Emil Dreyer.
*** Source: messier-objects.com
10/17/022 – Ephemeris – Andromeda, damsel in distress
This is Ephemeris for Monday, October 17th. Today the Sun will be up for 10 hours and 53 minutes, setting at 6:54, and it will rise tomorrow at 8:02. The Moon, at last quarter today, will rise at 12:18 tomorrow morning
In the east at 9 this evening can be found a large square of stars, the Great Square of Pegasus the upside down flying horse. The square is standing on one corner. What looks like its hind legs stretching to the left from the left corner star is another constellation, Andromeda the chained princess. She is seen in the sky as two nearly horizontal but diverging curved strings of stars that curve upward. She was doomed due to her mother, Queen Cassiopeia’s boasting, which angered the god Poseidon. She was rescued by the hero Perseus, a nearby constellation, riding his steed Pegasus. Andromeda’s claim to scientific fame is the large galaxy seen as a faint fuzzy spot with the naked-eye just above the upper line of stars. The Great Andromeda Galaxy is two and a half million light years away.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hours). They may be different for your location.
Addendum
Andromeda finder animation looking east at 9 pm tonight, October 17, 2022. The left corner star of the Great Square of Pegasus is called Alpheratz, and actually belongs to Andromeda. The faint fuzzy spot labeled M31 is the Great Andromeda Galaxy, the Milky Way’s large neighbor. I’ll talk more about it tomorrow. Click on the image to enlarge it. Created using Stellarium and GIMP.
I’ve related Andromeda’s story in my post The Great Star Story of Autumn.
09/28/2021 – Ephemeris – Andromeda, a damsel in distress
This is Bob Moler with Ephemeris for Tuesday, September 28th. Today the Sun will be up for 11 hours and 50 minutes, setting at 7:28, and it will rise tomorrow at 7:38. The Moon, at last quarter today, will rise at 11:46 this evening.
In the east at 9 this evening can be found a large square of stars, the Great Square of Pegasus the flying horse. The square is standing on one corner. What looks like its hind legs stretching to the left from the left corner star is another constellation, Andromeda the chained princess. She is seen in the sky as two diverging curved strings of stars that curve upward. She was doomed due to her mother, Queen Cassiopeia’s boasting, which angered the god Poseidon. She was rescued by the hero Perseus, a nearby constellation, riding his steed Pegasus. Andromeda’s claim to astronomical fame is the large galaxy seen with the naked-eye just above the upper line of stars. The Great Andromeda Galaxy is two and a half million light years away.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT-4 hours). They may be different for your location.
Addendum
Andromeda finder animation surrounded by the other constellations in her story, except the monster, which will rise later. Click on the image to enlarge it. Created using Stellarium and GIMP.
Great Andromeda Galaxy finder chart. This image shows the galaxy almost to its fullest extent. In the finder animation above, the galaxy looks pretty much as it would to the naked eye. Click on the image to enlarge it. Created using Stellarium.
Astronomers often refer to this galaxy as M 31 for short. It was the 31st entry in Charles Messier’s catalog of objects that could be confused as being comets by comet hunters like himself. It was added in 1764. He didn’t care what these fuzzy objects were, just that they didn’t move against the background stars. Actually, M 31 is in the background. The stars are in the foreground, in our Milky Way Galaxy.
10/15/2020 – Ephemeris – The Great Andromeda Galaxy
This is Ephemeris for Thursday, October 15th. Today the Sun will be up for 10 hours and 58 minutes, setting at 6:57, and it will rise tomorrow at 8:00. The Moon, 1 day before new, will rise at 7:30 tomorrow morning.
The closest large galaxy to our Milky Way galaxy is the Great Andromeda Galaxy seen in the eastern sky when it gets dark. It is barely visible to the naked eye. To locate it first find the Great Square of Pegasus high in the east, standing on one corner. The left star of the square is the head of the constellation Andromeda. Follow two stars to the left and a bit downward, then two stars straight up. The galaxy is near that last star as a small smudge of light. Binoculars are the best way to see it as a thin spindle of light. Visually through a telescope one can see only the bright nucleus of the galaxy, that spans six Moon diameters in photographs. M31 is its most famous catalog designation and it is two and a half million light years away.
The event times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Andromeda animated finder, including the Great Andromeda Galaxy. I’ve added Cassiopeia that some folks use to find the galaxy. I start with the leftmost star of the Great Square of Pegasus that connects to Andromeda. I count off two star on the lower curve because they are brighter than the upper curve. Then count two stars up. Next to that top star is a little smudge. That is the core of the Great Andromeda Galaxy. Created using Stellarium and GIMP.
The moon superimposed on the Great Andromeda Galaxy, M31, for apparent size comparison. Created using Stellarium and the embedded image of the galaxy with that of the full Moon of October 31, 2020. M31 Image credit: Herm Perez License: “Feel free to use these images, if you use them in a commercial setting please attribute the source.”
10/08/2020 – Ephemeris – A lady with a not so hidden jewel
This is Ephemeris for Thursday, October 8th. Today the Sun will be up for 11 hours and 19 minutes, setting at 7:09, and it will rise tomorrow at 7:51. The Moon, 1 day before last quarter, will rise at 11:09 this evening.
The stars of the constellations Andromeda the chained princess look like they’re supposed to be the hind legs of Pegasus the flying horse which is high in the southern sky above Mars at 9 p.m. Andromeda is high in the southeast She is seen in the sky as two diverging curved strings of stars that curve to the left and up from the upper leftmost star of the Great Square of Pegasus. Her predicament was caused by her boastful mother Cassiopeia, and the wrath of the god Poseidon. She was rescued by the hero Perseus, a nearby constellation, riding his steed Pegasus. Andromeda’s claim to astronomical fame is the large galaxy barely visible to the unaided eye just above the upper line of stars, the Great Andromeda Galaxy 2.5 million light years away.
The event times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Andromeda animated finder, including the Great Andromeda Galaxy. I’ve added Cassiopeia that some folks use to find the galaxy. I start with the leftmost star of the Great Square of Pegasus that connects to Andromeda. I count off two star on the lower curve because they are brighter than the upper curve. Then count two stars up. Next to that top star is a little smudge. That is the core of the Great Andromeda Galaxy. Created using Stellarium and GIMP.
The Great Andromeda Galaxy (M31) and two of its satellite galaxies M31 (left) and M110. Image taken by Scott Anttila.
08/25/2020 – Ephemeris – The Great Andromeda Galaxy will collide with the Milky Way someday
This is Ephemeris for Tuesday, August 25th. Today the Sun will be up for 13 hours and 33 minutes, setting at 8:30, and it will rise tomorrow at 6:58. The Moon, at first quarter today, will set at 12:26 tomorrow morning.
Stars are at extreme distances compared to their sizes, even if one includes their planetary systems. Galaxies in a galaxy cluster are much closer with respect to their size. Astronomers have determined that our Milky Way galaxy will collide with the Great Andromeda galaxy, some two and a half million light years away, in about four and a half billion years. Don’t worry, it is very unlikely that any stars will collide during the event, though the solar system may be in for a wild ride. As the galaxies approach each other their beautiful spiral structures will begin to distort into tidal tails. Multiple passes of the two will occur before they will coalesce into one large elliptical galaxy. Other galaxies of the Local Group will join in over time.
The event times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Colliding galaxies. Note the tidal tails. Credit: Hubble Legacy Archive, ESA, NASA.
Original caption: This illustration shows a stage in the predicted merger between our Milky Way galaxy and the neighboring Andromeda galaxy, as it will unfold over the next several billion years. In this image, representing Earth’s night sky in 3.75 billion years, Andromeda (left) fills the field of view and begins to distort the Milky Way with tidal pull. (Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger)
Bob Moler's Ephemeris Blog 