10/06/2021 – Ephemeris – Let’s search for the naked-eye planets for this week
This is Ephemeris for Wednesday, October 6th. Today the Sun will be up for 11 hours and 26 minutes, setting at 7:13, and it will rise tomorrow at 7:48. The Moon is new today, and won’t be visible.
Let’s search for the naked-eye planets for this week. Venus should be visible in the southwestern evening twilight by 7:45 tonight. It will set at 8:52 pm. By 8 pm, Jupiter will be spotted in the south-southeastern sky. The Jupiter should be easy to spot at that hour. Saturn will be dimmer, but a bit higher and to its right. They will be visible into the morning hours, with Saturn setting first at 1:58 am, and Jupiter following at 3:20. Saturn’s rings can be seen in a spotting scope of about 20 power magnification. Though at that power the rings won’t appear separated from the planet, so Saturn will look like an elliptical disk. Jupiter’s 4 brightest moons are spread out, three on one side, and one on the other. They might all be visible in binoculars tonight.
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
Venus in evening twilight at 7:45 pm, about a half hour after sunset. Created using Stellarium.
Jupiter and Saturn at 8 pm, about 45 minutes after sunset tonight, October 6, 2021. Created using Stellarium.
Telescopic views of the bright planets (north up) as they would be seen in a small telescope, with the same magnification, this evening at 8 pm, October 6, 2021. Apparent diameters: Venus, 19.81″, 59.8% illuminated; Saturn 17.48″, its rings 40.73″; Jupiter, 45.55″. The ” symbol means seconds of arc (1/3600th of a degree.) Click on the image to enlarge it. Created using Cartes du Ciel (Sky Charts).
The naked-eye planets and the Moon at sunset and sunrise on a single night, starting with sunset on the right on October 6, 2021. The night ends on the left with sunrise on the 7th. Click on the image to enlarge it. Created using my LookingUp program.
10/05/2021 – Ephemeris – Can you spot the North American Nebula?
This is Bob Moler with Ephemeris for Tuesday, October 5th. Today the Sun will be up for 11 hours and 29 minutes, setting at 7:15, and it will rise tomorrow at 7:47. The Moon, 1 day before new, will rise at 7:46 tomorrow morning.
Most of what we see in the Milky Way are just masses of stars, but there are bright clouds of gas, or to name them properly: emission nebulae. These bright clouds are areas of star formation. It is the ultraviolet light from young massive stars that light up the clouds they were formed from. A bright one, easily visible in binoculars, is just about overhead at 9 p.m. Called the North American Nebula, a glow, that in photographs is shaped much like our continent, is just east of the star Deneb which is practically overhead in the evening. Deneb is the northernmost star of the Summer Triangle, and brightest star in Cygnus the swan or Northern Cross. There are many other nebulae in the Milky Way, visible in binoculars and small telescopes. Many enjoyable hours can be spent sweeping the Milky Way for nebulae and star clusters.
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
North American Nebula finder animation. I’ve dimmed down the stars a bit and increased the brightness of the Milky Way to aid in spotting the nebula. It requires dark skies to see it. I believe I can make it out with the naked eye too. Click on the image to enlarge it. Created using Stellarium and GIMP.
One of my old photographs of Deneb and the North American Nebula, digitized from a slide.
Better view of the North American Nebula taken by Scott Anttila.
10/04/2021 – Ephemeris – Why we can’t talk to the Perseverance rover on Mars right now
This is Ephemeris for Monday, October 4th. Today the Sun will be up for 11 hours and 32 minutes, setting at 7:17, and it will rise tomorrow at 7:46. The Moon, 2 days before new, will rise at 6:30 tomorrow morning.
NASA is no longer sending commands to its Perseverance rover or any of its assets roving or orbiting Mars now. The reason isn’t particularly sinister. It’s the approximately 26 month Mars solar conjunction. The Sun is a noisy radio source, and commands sent to or data received from these martian assets could be garbled. This affects everyone’s assets on or orbiting Mars, which includes the Europeans, India, China and the United Arab Emirates. For NASA, communication restrictions started two days ago and will last until the 14th. This will give the folks at JPL who are operating the Curiosity and Perseverance rovers some time off, and time to plan the next few months of activity.
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
Mars in solar conjunction. Looking at the inner solar system. Mars, near the bottom of the image, is 244.6 million miles (393.9 million kilometers) from Earth. Click on the image to enlarge it. Credit NASA’s Eyes app.
Mars beyond and to the upper left of the Sun yesterday. It’s tough to get intelligible radio signals through the solar corona. Credit: NASA/ESA SOHO* spacecraft. The annotation is mine.
* SOlar and Heliospheric Observatory, spacecraft in halo orbit around the Lagrangian L1 equilibrium point about 930,000 miles (1,500,000 kilometers) sunward of the Earth. This keeps the satellite roughly between the Sun and the Earth, instead of moving ahead of the Earth because it’s closer to the Sun.
10/01/2021 Ephemeris – Learn about exoplanets and have a star party tonight (virtually)
This is Bob Moler with Ephemeris for Friday, October 1st. Today the Sun will be up for 11 hours and 41 minutes, setting at 7:22, and it will rise tomorrow at 7:42. The Moon, 3 days past last quarter, will rise at 2:49 tomorrow morning.
The Grand Traverse Astronomical Society hold a virtual meeting and program at 8 pm tonight via Zoom. For the program, yours truly will present Finding Exoplanets. Exoplanets are planets found orbiting other stars or rogue planets floating in interstellar space alone. We’ve actually only seen a handful of exoplanets, so most are detected by their effects on their host star. A virtual star party will start around 9 pm, hosted by Dr. Jerry Dobek, astronomy professor at Northwestern Michigan College, but only if it’s clear in Traverse City. It will feature Jupiter and Saturn, wonders of the northern part of the summer Milky Way. Instructions to join the meeting and a link can be found on the society’s website, http://www.gtastro.org.
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
Finding Exoplanets title slide.
09/30/2021 – Ephemeris – Previewing October skies
This is Ephemeris for Thursday, September 30th. Today the Sun will be up for 11 hours and 44 minutes, setting at 7:24, and it will rise tomorrow at 7:41. The Moon, 2 days past last quarter, will rise at 1:42 tomorrow morning.
Let’s look at the skies for this month of October. The Sun will still be moving south rapidly. Daylight hours in the Interlochen/Traverse City area will drop from 11 hours and 41 minutes tomorrow to 10 hours 12 minutes on the 31st. The altitude of the sun above the southern horizon at local noon will be 42 degrees tomorrow, and will descend to 31 degrees on Halloween, also in the Interlochen/Traverse City area. The Straits area will have the sun a degree lower. Local noon, when the Sun is due south, will be about 1:30 pm in Interlochen and Traverse City. Bits of Halley’s comet will return later in the month as the Orionid meteor shower. However, it will have to compete with a nearly full moon.
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.
October Evening Star Chart
Star Chart for October 2021. (9 p.m. EDT, October 15, 2021) Click on image to enlarge. Created using my LookingUp program. Click on image to enlarge.
October Morning Star Chart
Star Chart for October mornings, 2021 (6 a.m. EDT, October 15, 2021). Click on image to enlarge. Created using my LookingUp program.
For a list of constellation names to go with the abbreviations, click here.
- Pointer stars at the front of the bowl of the Big Dipper point to Polaris, the North Star.
- Leaky dipper drips on Leo.
- Follow the arc of the handle of the Big Dipper to the star Arcturus.
- The Summer Triangle is in red.
- OriR – Orionid Radiant – Peak 22nd – Zenithal Hourly Rate = 20
Twilight Limits, Nautical and Astronomical
| EDT | |||||||
| Morning | Twilight | Evening | Twilight | Dark | Night | Moon | |
| Date | Astro. | Nautical | Nautical | Astro. | Start | End | Illum. |
| 2021-10-01 | 6h09m | 6h43m | 20h29m | 21h03m | 21h03m | 1h42m | 0.21 |
| 2021-10-02 | 6h10m | 6h44m | 20h27m | 21h01m | 21h01m | 2h49m | 0.13 |
| 2021-10-03 | 6h11m | 6h45m | 20h25m | 20h59m | 20h59m | 4h01m | 0.07 |
| 2021-10-04 | 6h13m | 6h47m | 20h23m | 20h57m | 20h57m | 5h15m | 0.02 |
| 2021-10-05 | 6h14m | 6h48m | 20h21m | 20h55m | 20h55m | 6h14m | 0 |
| 2021-10-06 | 6h15m | 6h49m | 20h19m | 20h54m | 20h54m | 6h15m | 0.01 |
| 2021-10-07 | 6h16m | 6h50m | 20h18m | 20h52m | 20h52m | 6h16m | 0.04 |
| 2021-10-08 | 6h18m | 6h52m | 20h16m | 20h50m | 20h50m | 6h18m | 0.1 |
| 2021-10-09 | 6h19m | 6h53m | 20h14m | 20h48m | 21h10m | 6h19m | 0.19 |
| 2021-10-10 | 6h20m | 6h54m | 20h12m | 20h46m | 21h53m | 6h20m | 0.29 |
| 2021-10-11 | 6h21m | 6h55m | 20h11m | 20h44m | 22h46m | 6h21m | 0.4 |
| 2021-10-12 | 6h23m | 6h57m | 20h09m | 20h43m | 23h50m | 6h23m | 0.51 |
| 2021-10-13 | 6h24m | 6h58m | 20h07m | 20h41m | – | 6h24m | 0.62 |
| 2021-10-14 | 6h25m | 6h59m | 20h06m | 20h39m | 1h00m | 6h25m | 0.72 |
| 2021-10-15 | 6h26m | 7h00m | 20h04m | 20h38m | 2h13m | 6h26m | 0.81 |
| 2021-10-16 | 6h28m | 7h01m | 20h02m | 20h36m | 3h25m | 6h28m | 0.89 |
| 2021-10-17 | 6h29m | 7h03m | 20h01m | 20h34m | 4h35m | 6h29m | 0.94 |
| 2021-10-18 | 6h30m | 7h04m | 19h59m | 20h33m | 5h43m | 6h30m | 0.98 |
| 2021-10-19 | 6h31m | 7h05m | 19h57m | 20h31m | – | – | 1 |
| 2021-10-20 | 6h33m | 7h06m | 19h56m | 20h30m | – | – | 1 |
| 2021-10-21 | 6h34m | 7h08m | 19h54m | 20h28m | – | – | 0.98 |
| 2021-10-22 | 6h35m | 7h09m | 19h53m | 20h26m | – | – | 0.94 |
| 2021-10-23 | 6h36m | 7h10m | 19h51m | 20h25m | – | – | 0.89 |
| 2021-10-24 | 6h37m | 7h11m | 19h50m | 20h24m | 20h24m | 20h56m | 0.82 |
| 2021-10-25 | 6h39m | 7h12m | 19h48m | 20h22m | 20h22m | 21h38m | 0.74 |
| 2021-10-26 | 6h40m | 7h14m | 19h47m | 20h21m | 20h21m | 22h29m | 0.66 |
| 2021-10-27 | 6h41m | 7h15m | 19h45m | 20h19m | 20h19m | 23h27m | 0.56 |
| 2021-10-28 | 6h42m | 7h16m | 19h44m | 20h18m | 20h18m | – | 0.46 |
| 2021-10-29 | 6h43m | 7h17m | 19h43m | 20h17m | 20h17m | 0h31m | 0.37 |
| 2021-10-30 | 6h45m | 7h19m | 19h41m | 20h15m | 20h15m | 1h39m | 0.27 |
| 2021-10-31 | 6h46m | 7h20m | 19h40m | 20h14m | 20h14m | 2h50m | 0.18 |
Twilight calendar was generated using Cartes du Ciel (Sky Charts).
See my blog post: Twilight Zone for the definitions of the different periods of twilight here: https://bobmoler.wordpress.com/2018/09/27/.
NASA Calendar of Planetary Events
Date Time ET Event
Oct 1 Fr Venus: 44.9° E
1 Fr 9:08 am Moon-Beehive: 3.3° S
6 We 7:05 am New Moon
7 Th 11:50 pm Mars Solar Conjunction
8 Fr 1:28 pm Moon Perigee: 363400 km
9 Sa 12:12 pm Mercury Inferior Conj.
9 Sa 2:36 pm Moon-Venus: 2.9° S
9 Sa 3:35 pm Moon Descending Node
10 Su S Taurid peak ZHR = 5 See IMO Calendar
12 Tu 5:09 am Moon South Dec.: 26.2° S
12 Tu 11:25 pm First Quarter
14 Th 3:12 am Moon-Saturn: 4.1° N
15 Fr 5:58 am Moon-Jupiter: 4.3° N
16 Sa 9:24 am Venus-Antares: 1.5° N
20 We 10:57 am Full Moon
21 Th 7:30 am Orionid Shower: ZHR = 20
23 Sa 7:47 am Moon Ascending Node
24 Su 11:30 am Moon Apogee: 405600 km
25 Mo 12:59 am Mercury Greatest Elongation: 18.4° W
26 Tu 12:04 pm Moon North Dec.: 26.3° N
27 We 4:40 pm Moon-Pollux: 2.8° N
28 Th 4:05 pm Last Quarter
28 Th 5:32 pm Moon-Beehive: 3.6° S
29 Fr 5:59 pm Venus Greatest Elongation: 47° E
Nov 1 Mo Venus: 47° E
All event times are given for UTC-4 hr: Eastern Daylight Saving Time.
Sky Events Calendar by Fred Espenak and Sumit Dutta (NASA’s GSFC),
http://eclipse.gsfc.nasa.gov/SKYCAL/SKYCAL.html.
If you go to the above site, you can print out a list like the above for the entire year or calendar pages for your time zone.
Sun and Moon Rising and Setting Events
LU Ephemeris of Sky Events for Interlochen/TC October, 2021 Local time zone: EDT +-----------------------------------------------------------------------+ | DATE | SUN SUN DAYLIGHT| TWILIGHT* |MOON RISE OR ILLUM | | | RISE SET HOURS | END START |PHASE SET** TIME FRACTN| +=======================================================================+ |Fri 1| 07:41a 07:22p 11:41 | 08:25p 06:38a | Rise 02:49a 23%| |Sat 2| 07:42a 07:20p 11:38 | 08:23p 06:39a | Rise 04:01a 15%| +------+-----------------------+----------------+-----------------------+ |Sun 3| 07:43a 07:19p 11:35 | 08:21p 06:40a | Rise 05:15a 8%| |Mon 4| 07:44a 07:17p 11:32 | 08:20p 06:41a | Rise 06:30a 3%| |Tue 5| 07:46a 07:15p 11:29 | 08:18p 06:43a | Rise 07:46a 0%| |Wed 6| 07:47a 07:13p 11:26 | 08:16p 06:44a |New Set 07:41p 0%| |Thu 7| 07:48a 07:11p 11:23 | 08:14p 06:45a | Set 08:06p 3%| |Fri 8| 07:49a 07:09p 11:20 | 08:12p 06:46a | Set 08:35p 9%| |Sat 9| 07:51a 07:08p 11:17 | 08:11p 06:47a | Set 09:09p 17%| +------+-----------------------+----------------+-----------------------+ |Sun 10| 07:52a 07:06p 11:14 | 08:09p 06:49a | Set 09:53p 26%| |Mon 11| 07:53a 07:04p 11:11 | 08:07p 06:50a | Set 10:46p 37%| |Tue 12| 07:54a 07:02p 11:08 | 08:05p 06:51a |F Qtr Set 11:50p 48%| |Wed 13| 07:56a 07:01p 11:05 | 08:04p 06:52a | Set 01:00a 59%| |Thu 14| 07:57a 06:59p 11:02 | 08:02p 06:54a | Set 02:13a 70%| |Fri 15| 07:58a 06:57p 10:59 | 08:00p 06:55a | Set 03:25a 79%| |Sat 16| 07:59a 06:55p 10:56 | 07:59p 06:56a | Set 04:35a 87%| +------+-----------------------+----------------+-----------------------+ |Sun 17| 08:01a 06:54p 10:53 | 07:57p 06:57a | Set 05:43a 93%| |Mon 18| 08:02a 06:52p 10:50 | 07:56p 06:58a | Set 06:49a 97%| |Tue 19| 08:03a 06:50p 10:47 | 07:54p 07:00a | Set 07:54a 100%| |Wed 20| 08:05a 06:49p 10:44 | 07:52p 07:01a |Full Rise 07:07p 100%| |Thu 21| 08:06a 06:47p 10:41 | 07:51p 07:02a | Rise 07:29p 98%| |Fri 22| 08:07a 06:46p 10:38 | 07:49p 07:03a | Rise 07:53p 95%| |Sat 23| 08:09a 06:44p 10:35 | 07:48p 07:05a | Rise 08:22p 90%| +------+-----------------------+----------------+-----------------------+ |Sun 24| 08:10a 06:42p 10:32 | 07:46p 07:06a | Rise 08:56p 84%| |Mon 25| 08:11a 06:41p 10:29 | 07:45p 07:07a | Rise 09:38p 76%| |Tue 26| 08:13a 06:39p 10:26 | 07:44p 07:08a | Rise 10:29p 67%| |Wed 27| 08:14a 06:38p 10:23 | 07:42p 07:10a | Rise 11:27p 58%| |Thu 28| 08:15a 06:36p 10:21 | 07:41p 07:11a |L Qtr Rise 12:31a 48%| |Fri 29| 08:17a 06:35p 10:18 | 07:39p 07:12a | Rise 01:39a 38%| |Sat 30| 08:18a 06:33p 10:15 | 07:38p 07:13a | Rise 02:50a 29%| +------+-----------------------+----------------+-----------------------+ |Sun 31| 08:19a 06:32p 10:12 | 07:37p 07:14a | Rise 04:03a 19%| +-----------------------------------------------------------------------+ * Nautical Twilight ** Moonrise or moonset, whichever occurs between sunrise and sunset
Generated using my LookingUp for DOS program.
09/29/2021 – Ephemeris – Let’s search for the naked-eye planets for this week
This is Ephemeris for Wednesday, September 29th. Today the Sun will be up for 11 hours and 47 minutes, setting at 7:26, and it will rise tomorrow at 7:39. The Moon, 1 day past last quarter, will rise at 12:40 tomorrow morning.
Let’s search for the naked-eye planets for this week. Venus should be visible in the southwestern evening twilight by 7:45 tonight. It will set at 8:59 pm. By 8 pm, Jupiter will be spotted in the southeastern sky. The Jupiter should be easy to spot at that hour. Saturn will be dimmer, but a bit higher and to its right. They will be visible into the morning hours, with Saturn setting first at 2:26 am, with Jupiter following at 3:49. Saturn’s rings can be seen in a spotting scope of about 20 power magnification. Though at that power the rings won’t appear separated from the planet, so Saturn will look like an elliptical disk. Jupiter’s four brightest moons are spread out, two on each side. They all might be visible in binoculars tonight.
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
Venus in evening twilight at 7:45 pm, about a half hour after sunset tonight, September 29, 2021. Created using Stellarium.
Jupiter and Saturn in the southeast at 8 pm. Created using Stellarium.
Low magnification view of the waxing crescent Moon as it would appear at 6:30 am tomorrow, September 30, 2021. Created using Stellarium.
Telescopic views of the bright planets (north up) as they would be seen in a small telescope, with the same magnification, this evening at 8 pm, September 29, 2021. Apparent diameters: Venus, 18.65″, 62.6% illuminated; Saturn 17.68″, its rings 41.18″; Jupiter, 46.41″. The ” symbol means seconds of arc (1/3600th of a degree.) Click on the image to enlarge it. Created using Cartes du Ciel (Sky Charts).
The naked-eye planets and the Moon at sunset and sunrise on a single night, starting with sunset on the right on September 29, 2021. The night ends on the left with sunrise on the 30th. Click on the image to enlarge it. Created using my LookingUp program.
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.
09/27/2021 – Ephemeris – The native peoples constellations of the Crane and the Moose
This is Ephemeris for Monday, September 27th. Today the Sun will be up for 11 hours and 53 minutes, setting at 7:30, and it will rise tomorrow at 7:37. The Moon, 1 day before last quarter, will rise at 11:00 this evening.
The evening sky hosts two more of the constellations of the Anishinaabe native peoples of our area. Overhead, where the official constellation Cygnus the Swan is, or the Northern Cross is Ajijaak, the Sand Hill Crane flying northward through the Milky Way, wings outstretched, with its long legs trailing behind. In the eastern sky where the official constellation of Pegasus the flying horse is climbing the sky upside down is. His body is the Great Square, an informal constellation. To the Anishinaabe, it is the Mooz (Moose), who is upright. His magnificent antlers take up the dim official constellation of Lacerta the lizard between Pegasus and Cygnus. Also in the sky is Ojiig the Fisher, our Big Dipper, whose bloody tail will soon swoop down and paint the trees with their fall colors. (You can search for “Fisher” above right for his story, and his relevant appearances in autumn and late winter.)
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 Anishinaabe constellations of Ajijaak, the Crane and Mooz (Moose) compared to the official International Astronomical Union (IAU) constellations. Created using Stellarium and GIMP.
The Ojibwe constellation art is part of the latest versions of Stellarium. Ojibwe (Anishinaabe) constellation art by Annette S Lee and William Wilson from Ojibwe Sky Star Map Constellation Guide, ISBN 978-0-615-98678-4.
09/24/2021 – Ephemeris – Capricornus, home this season to Jupiter and Saturn
This is Bob Moler with Ephemeris for Friday, September 24th. Today the Sun will be up for 12 hours and 3 minutes, setting at 7:35, and it will rise tomorrow at 7:33. The Moon, halfway from full to last quarter, will rise at 9:26 this evening.
Nearly 2000 years ago the southernmost of the constellations of the zodiac was Capricornus the water goat. That’s why the latitude on the Earth where the Sun is overhead on the winter solstice is called the Tropic of Capricorn. Not anymore, Sagittarius, one constellation west, has that honor today*. Capricornus is large, but made up of dim stars. To me, it looks like a 45 degree isosceles triangle, long side up, but which all the sides are sagging. The constellation is found low in the south at 10 to 11 p.m. The image that is supposed to be represented by the stars is that of a goat whose hind quarters are replaced by a fish’s tail, not a mermaid but a mer-goat. This autumn, Jupiter is at the left end of Capricornus, with Saturn on the right.
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.
The reason for the shift is lunisolar precession, which I talked about yesterday.
Addendum
Capricornus w/Jupiter & Saturn finder animation for 10 pm, September 24, 2021. Created using Stellarium and GIMP.
09/23/2021 – Ephemeris – The Earth’s axial tilt gives us our seasons
This is Bob Moler with Ephemeris for Thursday, September 23rd. Today the Sun will be up for 12 hours and 6 minutes, setting at 7:37, and it will rise tomorrow at 7:32. The Moon, 3 days past full, will rise at 9:03 this evening.
The Earth has an axial tilt* of about 23 and a half degrees, which gives us our seasons. Because the Earth rotates on its axis, it has a slight equatorial bulge. Earth’s polar diameter is 7,900 miles (12,714 kilometers) while its equatorial diameter is 7,926 miles (12,756 kilometers), a difference of 26 miles (42 kilometers). The gravitational tug on that equatorial bulge by the Moon and Sun actually keeps the tilt stable, but does cause the Earth’s axis to precess like a top slowing down. It’s why Polaris will no longer be our North Pole star in centuries to come, just as it wasn’t in centuries past. It’s also why the constellations of the zodiac no longer align with the astrological signs of Ptolemy’s zodiac of the second century AD.
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.
* Astronomers call axial tilt “obliquity” or “obliquity of the ecliptic”.
Addendum
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. Image credit: Open Course: Astronomy.
Precession of a spinning top: the spin axis traces the surface of a cone. The axis, in the case of the Earth, traces a circle of radius 23.5 degrees on the sky. Credit NASA.
The 25,700-year cycle of precession traced on the sky 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: Tfr000, caption: Wikipedia.
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