Archive
Ephemeris: 05/22/2025 – Finding Hercules among the spring stars
This is Bob Moler with Ephemeris for Thursday, May 22nd. Today the Sun will be up for 15 hours and 5 minutes, setting at 9:12, and it will rise tomorrow at 6:06. The Moon, 2 days past last quarter, will rise at 3:51 tomorrow morning.
In the eastern sky at 11 PM about a third of the way along the line from the bright star Vega in the east northeast and Arcturus high in the southeast is the constellation of Hercules the hero. It’s kind of hard to spot, although it’s one distinctive feature is the box of four stars called the Keystone of Hercules which means it’s wider at the top than at the bottom. That is his body. He’s upside down in the sky according to how they draw the picture of Hercules. Most of his stars are reasonably dim. This is the great hero of Greek myth. While in the winter sky the bright and splashy constellation of Orion the hunter, was kind of a hard luck hero, with no real accomplishments. Hercules has an astronomical jewel that I’ll talk about tomorrow.
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: 05/20/2025 – Corona Borealis, Ariadne’s Crown
This is Ephemeris for Tuesday, May 20th. Today the Sun will be up for 15 hours and 1 minute, setting at 9:10, and it will rise tomorrow at 6:08. The Moon, at last quarter today, will rise at 3:12 tomorrow morning.
There are two bright stars in the eastern part of the sky. High in the southeast at 11 PM is Arcturus, and in the east northeast, lower down is the star Vega. A third of the way between Arcturus and Vega is a small arc of stars called Corona Borealis, the northern crown. It is a small constellation. The brightest star in it is called Alphecca. According to Greek mythology it is the crown given to Princess Ariadne, daughter of King Minos of Crete. Of interest in the next year or so is a possibility of a nova or bright star appearing just south of that arc of stars for about a week. It is a recurrent nova, which explodes about every 80 years. The last time was in 1946, so the next time would be within the next year or so. And astronomers are breathlessly waiting for that to happen.
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: 05/16/2025 – Two bright stars, alike but different
This is Bob Moler with Ephemeris for Friday, May 16th. Today the Sun will be up for 14 hours and 52 minutes, setting at 9:05, and it will rise tomorrow at 6:12. The Moon, halfway from full to last quarter, will rise at 1:21 tomorrow morning.
Two stars which I’ve been known to confuse in the twilit sky in late spring and late summer are Arcturus and Vega. These stars have about the same brightness and in some lists of stars swap places between the 4th and 5th brightest stars in the sky. Arcturus is an orangish star, now high in the southern sky in the evening, while Vega is a pure white star which to my eyes tends towards a little tinge of blue. Vega is high in the south, actually almost overhead, in the late summer. Now, in mid to late Spring Vega is rather low in the northeastern sky. Arcturus is a cool star on the outside which has depleted the hydrogen in its core and is a red giant star, while the younger and more massive Vega, still turning hydrogen into helium.
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: 04/25/2025 – The star that opened a World’s Fair
This is Ephemeris for Arbor Day, Friday, April 25th. Today the Sun will be up for 13 hours and 59 minutes, setting at 8:40, and it will rise tomorrow at 6:39. The Moon, 2 days before new, will rise at 5:50 tomorrow morning.
High in the eastern sky at 10 tonight can be found the kite shaped constellation of Boötes the herdsman, chasing or herding the Great Bear Ursa Major of which the Big Dipper is the hind end, across the sky. The bright star at the base of the kite is the 4th brightest nighttime star, Arcturus. It can be found and name remembered by first locating the Big Dipper and by following the arc or curve of the handle to Arcturus. This star is an orange-colored giant star, 37 light years away. Its light was used to open the 1933 Chicago Worlds Fair believing its light left the star in 1893 the year of the previous Chicago Worlds Fair. It turns out that Arcturus is 3 light years closer than what they thought.
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
For more on how they did it go to: https://chicagology.com/centuryprogress/1933fair54/
Ephemeris: 04/21/2025 – Follow the spike to Spica
This is Ephemeris for Monday, April 21st. Today the Sun will be up for 13 hours and 47 minutes, setting at 8:35, and it will rise tomorrow at 6:46. The Moon, 1 day past last quarter, will rise at 4:25 tomorrow morning.
In the south-southeast at 10:30 p.m. is the bright star Spica, which can be found from all the way back overhead to the Big Dipper. Follow the arc of the handle of the Big Dipper to the bright star Arcturus below it in the east-southeast. Then straighten the curve of the arc to a straight spike which points to Spica, the brightest star in Virgo the virgin. Arcturus is much brighter than Spica and has an orange tint to Spica’s bluish hue. In fact, Spica is the bluest of the 21 first magnitude stars. That means that it has a really hot surface temperature. Actually, Spica is really two blue-white stars orbiting each other in 4 days. Spica is 250 light years away. It also was an important star to the ancient Greeks. One temple was built and aligned to its setting point. 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.
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: 04/14/2025 – Follow the arc to Arcturus
This is Ephemeris for Monday, April 14th. Today the Sun will be up for 13 hours and 27 minutes, setting at 8:27, and it will rise tomorrow at 6:57. The Moon, 2 days past full, will rise at 10:36 this evening.
The fourth or fifth-brightest nighttime star, depending on whose list you see, is now up in the east in the evening. It is Arcturus, a bright star with an orange hue. It can be found otherwise by finding the Big Dipper and tracing out and extending the curve of the handle and “Follow the arc of the handle to Arcturus”, to remember the name of the star and how to find it. Arcturus is about 37 light years from us and is moving quite rapidly across the sky, compared to most stars, though one would not notice it to the naked eye in one’s lifetime. Arcturus is slightly more massive than our Sun, and about 7 billion years old, and is entering its red giant stage of life after using all the hydrogen fuel in its core. Our Sun, being slightly less massive will survive on hydrogen a bit longer.
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: 05/28/2024 – Finding Spica and Virgo
This is Ephemeris for Tuesday, May 28th. Today the Sun will be up for 15 hours and 15 minutes, setting at 9:18, and it will rise tomorrow at 6:01. The Moon, 2 days before last quarter, will rise at 2:06 tomorrow morning.
The Big Dipper, near the zenith at 10:30 pm points to several stars and constellations. It’s handle points to two bright stars. First we follow the arc of the handle to the bright orange star Arcturus, the 4th brightest nighttime star. The reason I say nighttime is that the Sun is a star also, but by definition is not out at night. The arc to Arcturus is a way to find Arcturus and a clue to its name. Arcturus, high in the south-southeast, lies at the base point of the kite shaped constellation of Boötes the herdsman. From Arcturus, straighten out the arc to a spike and one soon arrives at Spica a blue-white star in Virgo the virgin, now in the south. Spica is also sometimes pronounced ‘Speeka’.
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
Ephemeris: 05/27/2024 The evening sky is transitioning into summer
This is Bob Moler with Ephemeris for Memorial Day, Monday, May 27th. Today the Sun will be up for 15 hours and 14 minutes, setting at 9:17, and it will rise tomorrow at 6:02. The Moon, 3 days before last quarter, will rise at 1:36 tomorrow morning.
The sky tonight at 10:30 is beginning to show the transition from spring to summer. Antares in Scorpius is very low in the southeast, rising and chasing away Orion who has disappeared in the West. According to Greek mythology, at least in one story, Orion was killed by the sting of a giant scorpion and so neither he nor Scorpius the scorpion can be in the sky at the same time. The bright star Spica in Virgo the virgin is due South at that time, with Leo the lion in the southwest. Very high in the southeast is the star Arcturus. The Big Dipper is overhead. And in the east-northeast high up this is the bright star Vega, one of the stars of the summer triangle. The second star of the triangle Deneb is lower in the northeast. The third star has yet to rise.
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
Ephemeris: 05/06/2024 – The star Arcturus: Not from around here
This is Ephemeris for Monday, May 6th. Today the Sun will be up for 14 hours and 29 minutes, setting at 8:54, and it will rise tomorrow at 6:23. The Moon, 1 day before new, will rise at 5:53 tomorrow morning.
Arcturus, a red giant star in the constellation of Boötes the herdsman, is about two thirds the way up the sky in the east-southeast at 10 pm. It’s one of the earliest stars to appear in twilight, being nearly tied in brightness with Vega, a white star low in the northeast. A pointer to Arcturus is the handle of the Big Dipper, following the arc of the handle to Arcturus. Though only 37 light years away, it’s not from around here. It’s passing through the galactic disk from north to south. Arcturus is about 7 billion years old, and is about 8% more massive than our Sun. It appears to be starting its red giant phase, after running out of hydrogen to fuse into helium in its core, and is beginning to fuse the helium. It’s 25 times the size of the Sun and 170 times brighter, and a preview of our Sun when it gets that old.
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
* Hertzsprung-Russell Diagram of a star’s surface (photosphere) temperature vs luminosity. The Main Sequence is where a star lives when it is burning hydrogen, and spends most of its life.
Ephemeris: 04/29/2024 – Corona Borealis, the Northern Crown
This is Ephemeris for Monday, April 29th. Today the Sun will be up for 14 hours and 11 minutes, setting at 8:46, and it will rise tomorrow at 6:33. The Moon, 2 days before last quarter, will rise at 2:58 tomorrow morning.
About a third of the way up the sky in the east at 10 p.m. can be found a small but easily spotted constellation of Corona Borealis, the Northern Crown. It is located just below the kite shaped constellation of Boötes, with its bright star Arcturus at the right. The Northern Crown is a three-quarter circle of stars, like a tiara, with a brighter star Alphecca at the bottom. Alphecca in Arabic means “The bright star of the broken ring of stars”, which is an accurate description of it. Check it out now for later this year we expect to have a bright star appear just below it. That star is T Coronae Borealis a recurrent Nova or exploding star. They occur when a white dwarf star is orbiting with a large red giant star and accumulating gas from that red giant star until it explodes.
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
Bob Moler's Ephemeris Blog 