Archive
07/17/2023 – Ephemeris – Arcturus, a look at the Sun’s future
This is Ephemeris for Monday, July 17th. Today the Sun will be up for 15 hours and 11 minutes, setting at 9:24, and it will rise tomorrow at 6:14. The Moon is new today, and won’t be visible.
Arcturus, a red giant star, is about two thirds the way up the sky in the southwest at 10:30 or 11 p.m. It’s one of the earliest stars to appear in twilight, being nearly tied in brightness with Vega, a white star about as high in the east. 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
06/09/2023 – Ephemeris – How to find Corona Borealis, the Northern Crown
This is Bob Moler with Ephemeris for Friday, June 9th. Today the Sun will be up for 15 hours and 29 minutes, setting at 9:27, and it will rise tomorrow at 5:57. The Moon, 1 day before last quarter, will rise at 2:13 tomorrow morning.
High in the southeast at 11 p.m. can be found a small but easily spotted constellation of Corona Borealis, the Northern Crown. It is located just east or left of the kite shaped constellation of Boötes, with its bright star Arcturus at the bottom. The Northern Crown is a three-quarters circle of stars, like a tiara, with a brighter star Alphecca at the bottom. Alphecca in Arabic means “Bright star of the broken ring of stars”. According to Greek mythology it belonged to Princess Ariadne, daughter of King Minos of Crete who helped Theseus escape from the Labyrinth of the Minotaur, only to be abandoned by him on an island. To the Native Chippewa and Ottawa of our area it is the Sweat Lodge.
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
Next Monday I will post about Hercules.
06/08/2023 – Ephemeris – The first stars that appear tonight
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04/21/2023 – Ephemeris – The first major meteor shower of spring reaches peak this weekend
This is Ephemeris for Friday, April 21st. Today the Sun will be up for 13 hours and 46 minutes, setting at 8:35, and it will rise tomorrow at 6:47. The Moon, 1 day past new, will set at 10:44 this evening.
Saturday night and Sunday morning will see the peak of the Lyrid meteor shower. This is the first of two major meteor showers of spring. The other one in two weeks will have to compete with a full Moon. This meteor shower will be visible all night. At the end of twilight the radiant of the shower, where the meteors will seem to come from, will be low in the northeast, to the right of the bright star Vega in the constellation of Lyra the harp, for which the meteor shower is named. The radiant point is actually between the constellations of Lyra and Hercules. Only 15 to 20 meteors an hour will be expected when the radiant is nearly overhead as morning twilight starts in the 5 am hour. The most famous meteor shower, for us, is the Perseids of August reaching peak on the morning of the 13th of August which will be seen in dark skies for most of the night.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT –4 hours). They may be different for your location.
Addendum
Lyrid radiant at 11 pm, looking to the east-northeast. The meteors will be seen all over the sky, but their tracks can be traced back to the radiant point, like the parallel rails of a train track recede to a point in the distance. Created using Stellarium.
01/09/2023 – Ephemeris – The Summer Triangle is still with us in the early evening
This is Ephemeris for Monday, January 9th. Today the Sun will be up for 9 hours and 1 minute, setting at 5:21, and it will rise tomorrow at 8:18. The Moon, 3 days past full, will rise at 7:56 this evening.
The bright Moon is now slowly leaving the evening sky tonight, giving us nearly an hour of dark skies after 7 pm. At 7pm, Orion is holding forth in the east-southeast. At that time, also, the Summer Triangle is still in the sky, west and northwest. The Northern Cross, which is also the constellation of Cygnus the swan, is standing upright in the west northwestern sky. Its top star Deneb, dimmest of the three Summer Triangle stars, will not set for observers north of Traverse City, though it will take a flat northern horizon and exceptionally clear skies to spot it at its lowest in the north. Altair, the southernmost of the triangle stars will set first in the west at 7:57 pm, Vega, the brightest will set in the northwest at 9:41 pm.
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
The setting Summer Triangle and Northern Cross in the west and northwestern sky at 7 pm tonight, January 9th.
07/14/2022 – Ephemeris – The dimmest Summer Triangle star is actually the brightest
This is Ephemeris for Thursday, July 14th. Today the Sun will be up for 15 hours and 15 minutes, setting at 9:26, and it will rise tomorrow at 6:11. The Moon, 1 day past full, will rise at 10:49 this evening.
This evening, when it gets dark enough, the bright star Deneb in Cygnus the swan will be high in the east-northeast. I’ll cover Cygnus tomorrow when the sky is darker. Deneb is the dimmest star of the summer triangle. Of the other stars of the triangle, Vega is higher in the east, while Altair is lower in the southeast. Deneb’s apparent magnitude, or brightness as seen from Earth, makes it the dimmest of the three bright stars. That’s because of its vast distance of maybe 1,550 light years, 57 times the distance of Vega. If brought as close as Vega, Deneb would be as bright, at least, as the first quarter moon. It is possibly as bright as 196 thousand Suns; and it’s a huge star, possibly as large in diameter as the orbit of the Earth. For all this, it is only 23 or so times the mass of the Sun.
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
The Summer Triangle. Created using Stellarium and The Gimp.
If you put Deneb in the search box, you will find that the content of the posts, over the years, about the star are nearly identical. However, the distance estimates vary widely. It is too far away for trigonometric parallax measurements by earth based telescopes. Though in the range of ESA’s Hipparcos and Gaia satellites, it is too bright. So other less accurate measurements are used. I don’t think it involves coin flipping. The assumed distance also affects estimates of luminosity, and mass.
07/07/2022 – Ephemeris – A closer look at the bright star Vega
This is Bob Moler with Ephemeris for Thursday, July 7th. Today the Sun will be up for 15 hours and 25 minutes, setting at 9:30, and it will rise tomorrow at 6:05. The Moon, 1 day past first quarter, will set at 1:53 tomorrow morning.
Vega, in the constellation Lyra the harp, is the highest star In the east and brightest star of the Summer Triangle also rising in that direction. It is an important and much studied star, first as a standard for brightness for the magnitude scale at almost exactly zero. It also has two fields of debris orbiting it. In 1983 the Infrared Astronomy Satellite, IRAS, discovered an excess of infrared radiation coming from the star. It seems now that there are two orbiting rings, one warm, and the other cold. This is somewhat like the two disks the Sun has: The asteroid belt between Mars and Jupiter and the Kuiper belt, beyond Neptune. No planets have yet been discovered around Vega, but I wouldn’t bet against it.
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
Animated Lyra finder chart. The lyre image not supplied by Stellarium but is from The World’s Earliest Music by Hermann Smith, Figure 60, A Project Gutenberg E-Book, and captioned “The Chelys or Greek Tortoiseshell Lyre”. Vega is the brightest star in Lyra, and the brightest star of the Summer Triangle. The other stars of the triangle are Deneb and Altair. Created using Stellarium.
Vega possesses two debris fields, similar to our own solar system’s asteroid and Kuiper belts. Astronomers continue to hunt for planets orbiting Vega, but as of May 2020 none have been confirmed. More info: bit.ly/VegaSystem Credit: NASA/JPL-Caltech
06/28/2022 – Ephemeris – Finding the celestial harp
This is Ephemeris for Tuesday, June 28th. Today the Sun will be up for 15 hours and 32 minutes, setting at 9:32, and it will rise tomorrow at 6:00. The Moon is new today, and won’t be visible.
High in the east at 11 p.m. can be found a bright star just above a small, narrow, but very distinctive parallelogram of stars. They are the stars of the constellation Lyra the harp. The bright star is Vega, the 4th or 5th brightest nighttime star*, and currently the topmost star of the Summer Triangle. To the Romans, the star Vega represented a falling eagle or vulture. Apparently they never made the distinction between the two species. It is a pure white star and serves as a calibration star for color and brightness. In the evening, it is the top-most star of the Summer Triangle. The harp, according to Greek mythology, was invented by the god Hermes. The form of the harp, in the sky, is as he had invented it: by stretching strings across a tortoise shell. Hermes gave it to his half-brother Apollo, who in turn gave it to the legendary musician Orpheus.
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.
*Vega’s rival for the fourth spot on the brightness list is Arcturus to it’s west. Wikipedia’s source says that Arcturus is slightly brighter. Stellarium’s source says Vega is brighter. The difference is a few hundredths of a magnitude. However, they are of different colors. Vega is pure white, while Arcturus is yellow-orange because it has a cooler surface temperature than Vega. Check them out for yourself.
Addendum
Animated Lyra finder chart. The lyre image not supplied by Stellarium but is from The World’s Earliest Music by Hermann Smith, Figure 60, A Project Gutenberg E-Book, and captioned “The Chelys or Greek Tortoiseshell Lyre”. The three names stars are the stars of the Summer Triangle in the eastern sky these evenings of late June. Created using Stellarium.
06/27/2022 – Ephemeris – Finding the Summer Triangle
This is Ephemeris for Monday, June 27th. Today the Sun will be up for 15 hours and 33 minutes, setting at 9:32, and it will rise tomorrow at 5:59. The Moon, 1 day before new, will rise at 5:13 tomorrow morning.
We’re nearly a week into summer, and the asterism or informal constellation called the Summer Triangle can be seen rising in the east as it gets dark. Highest of the three bright stars is Vega in the constellation Lyra the harp, whose body is seen in a narrow parallelogram nearby. The second star of the triangle is Deneb, in Cygnus the swan, lower and left of Vega, It appears dimmer than Vega because it is by far the most distant of the three. The third star of the Summer Triangle is seen farther below and a right of Vega. It is Altair in Aquila the eagle, and the closest. Altair is 16.5 light years away, Vega is 27 light years, while Deneb may be a whopping 2,600 light years away. One light year is 6 trillion miles (9 trillion kilometers).
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
The Summer Triangle finder animation showing first the unlabeled sky, Then the Summer Triangle with the stars labeled, then the constellations of those stars. Created using Stellarium and GIMP.
07/06/2021 – Ephemeris – Looking at the constellation of Lyra the harp
This is Ephemeris for Tuesday, July 6th. Today the Sun will be up for 15 hours and 26 minutes, setting at 9:30, and it will rise tomorrow at 6:05. The Moon, 3 days before new, will rise at 3:56 tomorrow morning.
High in the east at 11 p.m. can be found a bright star just above a small, narrow, but very distinctive parallelogram of stars. They are the stars of the constellation Lyra the harp. The bright star is Vega, the 5th brightest night-time star. To the Romans, the star Vega represented a falling eagle or vulture. Apparently they never made the distinction between the two species. It is a pure white star and serves as a calibration star for color and brightness. In the evening, it is the top-most star of the Summer Triangle. The harp, according to Greek mythology, was invented by the god Hermes. The form of the harp, in the sky, is as he had invented it: by stretching strings across a tortoise shell. Hermes gave it to his half-brother Apollo, who in turn gave it to the legendary musician Orpheus.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT-4). They may be different for your location.
Addendum
Animated Lyra finder chart. The lyre image not supplied by Stellarium but is from The World’s Earliest Music by Hermann Smith, Figure 60, A Project Gutenberg E-Book, and captioned “The Chelys or Greek Tortoiseshell Lyre”. Click on the image to enlarge it. Created using Stellarium and GIMP.
Bob Moler's Ephemeris Blog 