Archive

Author Archive

Ephemeris Extra: 07/02/2024 – A closer look at Corona Borealis

July 2, 2024 Comments off

Adapted from an article that ran in the Stellar Sentinel, the July 2024 newsletter of the Grand Traverse Astronomical Society.

Corona Borealis in relation to some of its neighboring constellations and bright stars. Created using Stellarium.

A small constellation is getting a lot of attention this year because we expect a bright nova to appear in it sometime in the next few months. The constellation is Corona Borealis, the Northern Crown. It is a small constellation between the Boötes and the bright star Arcturus and Hercules, and farther off to the east the bright star Vega. Corona Borealis contains seven stars in the 2/3 circle of stars. Its brightest star is the third star from the right. It’s the second magnitude star called Alphecca. In Arabic, it means The Bright Star of the Broken Ring of Stars, which is a pretty good description of it. It is also known as Gemma though it sounds like a gem in a crown, it actually means blossom which would appear in a floral crown.

In Greek mythology the crown was given to the Princess Ariadne. The story goes like this. During the time of the Minoan civilization on Crete, It was ruled by King Minos, whose daughter was Ariadne. The Minoans apparently had defeated Athens in battle and had extracted tribute from them. That yearly tribute being the sacrifice of the young man or maiden to enter the Labyrinth which was home to a monster called the Minotaur. In this story a fellow by the name of Theseus from Athens was sent to Crete to face the Minotaur. He fell in love with Ariadne, but he had to enter the Labyrinth, so she provided him with a spool of thread so he could find his way back out again after he had slain the Minotaur, if he was able to. He entered the Labyrinth and found the Minotaur. Theseus was able to slay the beast, and was able to follow the thread back out. Theseus and Ariadne fled to the Island of Naxos where he married her. However, he soon abandoned her. As consolation, the god Dionysus gave her a crown. She kept the crown until she remarried, and it was placed in the sky where we see it today.

For the Anishinaabe native peoples of our area Corona Borealis becomes the Sweat Lodge. Other indigenous peoples of North America see these stars as circles of maidens, or other circles. To the Aborigines of Australia who see Corona Borealis very low in the north, it’s Woomera, the boomerang.

The location and expected brightness of T Coronae Borealis (T CrB) when it goes nova later this year.


The constellation has two famous variable stars. The one we’re expecting to flare up this year, up to second magnitude as a nova, is T Coronae Borealis (T CrB), sometimes called the Blaze Star. It was recorded in 1866 and at even earlier times, and was naked eye for eight days, dropping a half magnitude per day. It also blazed forth in 1946, making it one of the few known recurrent novas. In 1946 the star, normally 10th magnitude, barely visible in binoculars, underwent a slight dimming about 11 months before it blazed forth as a nova. This has already happened last year, so we are expecting it soon to blaze forth again. It will appear to the lower left, just outside the circle of stars in the crown, and will grow as bright as Alphecca.

Novas, also in the case of T CrB, are close binary stars containing a large star and a white dwarf. A white dwarf is a star at the end of its life, and has run out of hydrogen or other light elements in its core to keep it sustained. So it shrinks down to about the size of the Earth, even though it has the mass of the Sun or a little more. It orbits with the larger star and is basically siphoning off gas from that large star onto its surface, enough gases accumulate on the star for a thermonuclear reaction to occur, and it becomes a nova, brightening thousands of times for a few days. The white dwarf survives to do it all over again in some cases.

Corona Borealis, pointing out the location of variable stars R CrB and T CrB. Created using Stellarium.

Corona Borealis’ other famous variable star is R Coronae Borealis, a star that’s normally about 6th magnitude that irregularly dips down to 10th or even dimmer. The mechanism for this appears to be that the star is surrounded by clouds of dust that periodically block it from our view.

If you’re interested in observing variable stars, check out the American Association of Variable Star Observers: https://www.aavso.org/

Corona Australis finder
Corona Australis finder chart, for around midnight August 2nd.

If there’s a Northern Crown, there should be a Southern Crown, and there is. It is Corona Australis made of dim stars, and it is located just below the constellation of Sagittarius, right below the Teapot asterism, which is very low on our southern horizon after midnight this month, but better seen in August.

Ephemeris: 7/02/2024 – Antares and the scorpion

July 2, 2024 Comments off

This is Bob Moler with Ephemeris for Tuesday, July 2nd. Today the Sun will be up for 15 hours and 29 minutes, setting at 9:31, and it will rise tomorrow at 6:02. The Moon, 3 days before new, will rise at 3:26 tomorrow morning.

The constellation of Scorpius the scorpion is low in the south at 11 PM these nights. It’s bright star Antares will pass due south at 11:30 this evening. Antares is an interesting star in that it is a red giant star, and its name Antares* means “Rival of Mars” alluding to the fact that it and Mars appears to be the same color. And about every two years Mars passes near Antares, so unless you know your stars and planets you could mistake them for each other. Antares lies at the heart of the scorpion. To its upper right is the front part of its body and claws, and the trail of stars running down the other way, nearly to the horizon, in the south and back up in the south-southeast to the two stars of its stinger make its characteristic tail.

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.

*Breaking down Antares: Ant (Anti, against) – Ares (The Greek god of war the Romans called Mars).

Addendum

Scorpius Finder in four frames
Scorpius Finder in four frames. The 1st frame is the star field above the southern horizon as it might appear at 11 pm, July 2nd. The 2nd frame shows the constellation lines of Scorpius. I differ a bit from Stellarium in the lines above right of Antares. The 3rd frame is the constellation art that comes with Stellarium of Scorpius. The 4th frame is the star field again with the constellation lines, but seen without the horizon or atmospheric extinction getting in the way. The Arabs may have thought Scorpius was a larger constellation. There are two stars at the upper right corner of the frame that they saw belonged to Scorpius, which now belong to Libra. The upper one, nearest the top, is Zubeneschamali which means northern claw. The one below it and nearest the right edge of the image is Zubenelgenubi, the southern claw. These names predate Libra being its own constellation.

Note for trivia fans: Zubeneschamali is the longest star name at 14 letters.

Ephemeris: 07/01/2024 – Previewing July’s skies

July 1, 2024 Comments off

This is Bob Moler with Ephemeris for Monday, July 1st. Today the Sun will be up for 15 hours and 30 minutes, setting at 9:31, and it will rise tomorrow at 6:02. The Moon, 3 days past last quarter, will rise at 2:50 tomorrow morning.

Let’s preview July’s skies. The Sun, having reached its northern solstice, is beginning to slide southward again, at first imperceptibly, then with greater speed. The daylight hours will decrease from 15 hours and 30 minutes today to 14 hours 40 minutes at month’s end. The daylight hours will be slightly shorter south of Interlochen, and slightly longer to the north. The altitude of the Sun at local noon, when it is due south will decrease from 68 degrees tomorrow to 63 degrees at month’s end. Despite the warmth, the Earth will reach its greatest distance from the Sun on Friday the 5th. Finally, a planet in the evening sky. Saturn will rise before midnight by mid-month, and Venus may be visible shortly after sunset by month’s end.

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

July Evening Star Chart

Star Chart for July 2024
Star Chart for July 2024 (11 p.m. EDT, July 15, 2024). Created using my LookingUp program. Click or tap on the image to enlarge it.

The planets and stars are plotted for the 15th at 11 p.m. EDT in the evening and 4 a.m. for the morning chart. These are the chart times. Note that Interlochen/Traverse City is located approximately 45 minutes behind our time meridian, West 75° longitude. (An hour 45 minutes behind our daylight saving time meridian during EDT). To duplicate the star positions on a planisphere you may have to set it to 1 hour 45 minutes earlier than the current time.
Note, the chart times of 11 p.m. and 4 a.m. are for the 15th. For each week before the 15th, add ½ hour (28 minutes if you’re picky). For each week after the 15th, subtract ½ hour, or 28 minutes. The planet positions are updated each Wednesday on this blog. For planet positions on dates other than the 15th, check the Wednesday planet posts on this blog for weekly positions.

July Morning Star Chart

Star Chart for July mornings, 2024
Star Chart for July mornings, 2024 (4 am EDT, July 15, 2024). Created using my LookingUp program. Click or tap on the image to enlarge it.

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, and
  • Extend like a spike to Spica.
  • The Summer Triangle is in red.
  • DAqR is the radiant of the South Delta Aquariid meteor shower (Peaks on the afternoon of the 27th)

Twilight Limits, Nautical and Astronomical

      EDT        
  Morning Twilight Evening Twilight Dark Night Moon
Date Astro. Nautical Nautical Astro. Start End Illum.
2024-07-01 3h35m 4h38m 23h00m 0h02m 0h02m 2h22m 0.16
2024-07-02 3h36m 4h38m 22h59m 0h01m 0h01m 2h51m 0.09
2024-07-03 3h37m 4h39m 22h59m 0h01m 0h01m 3h27m 0.04
2024-07-04 3h39m 4h40m 22h58m 0h00m 0h00m 3h39m 0.01
2024-07-05 3h40m 4h41m 22h58m 23h59m 23h59m 3h40m 0.00
2024-07-06 3h41m 4h42m 22h57m 23h58m 23h58m 3h41m 0.02
2024-07-07 3h43m 4h43m 22h56m 23h57m 23h57m 3h43m 0.05
2024-07-08 3h44m 4h44m 22h56m 23h55m 23h55m 3h44m 0.11
2024-07-09 3h46m 4h45m 22h55m 23h54m 23h54m 3h46m 0.17
2024-07-10 3h47m 4h46m 22h54m 23h53m 3h47m 0.25
2024-07-11 3h49m 4h47m 22h53m 23h52m 0h11m 3h49m 0.34
2024-07-12 3h51m 4h48m 22h52m 23h50m 0h27m 3h51m 0.43
2024-07-13 3h52m 4h50m 22h51m 23h49m 0h42m 3h52m 0.53
2024-07-14 3h54m 4h51m 22h50m 23h47m 0h59m 3h54m 0.62
2024-07-15 3h56m 4h52m 22h49m 23h46m 1h18m 3h56m 0.71
2024-07-16 3h58m 4h53m 22h48m 23h44m 1h41m 3h58m 0.80
2024-07-17 3h59m 4h55m 22h47m 23h42m 2h10m 3h59m 0.88
2024-07-18 4h01m 4h56m 22h46m 23h41m 2h49m 4h01m 0.94
2024-07-19 4h03m 4h57m 22h45m 23h39m 3h41m 4h03m 0.98
2024-07-20 4h05m 4h59m 22h44m 23h37m 1.00
2024-07-21 4h07m 5h00m 22h42m 23h36m 0.99
2024-07-22 4h09m 5h01m 22h41m 23h34m 0.96
2024-07-23 4h10m 5h03m 22h40m 23h32m 0.90
2024-07-24 4h12m 5h04m 22h38m 23h30m 0.81
2024-07-25 4h14m 5h06m 22h37m 23h28m 23h28m 23h43m 0.71
2024-07-26 4h16m 5h07m 22h35m 23h26m 23h26m 0.60
2024-07-27 4h18m 5h08m 22h34m 23h24m 23h24m 0h03m 0.49
2024-07-28 4h20m 5h10m 22h32m 23h22m 23h22m 0h26m 0.38
2024-07-29 4h22m 5h11m 22h31m 23h20m 23h20m 0h53m 0.28
2024-07-30 4h24m 5h13m 22h29m 23h18m 23h18m 1h26m 0.18
2024-07-31 4h26m 5h14m 22h28m 23h16m 23h16m 2h08m 0.11

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

Jul  1  Mo            Venus: 7.4° E
     1  Mo   2:27 pm  Moon-Mars: 4.2° S
     2  Tu  11:31 am  Moon-Pleiades:  .3° N
     4  Th   8:08 pm  Moon North Dec.: 28.4° N
     5  Fr   1:59 am  Aphelion: 1.0167 AU
     5  Fr   6:57 pm  New Moon
     6  Sa   5:12 pm  Mercury-Beehive:  .1° S
     7  Su  12:04 pm  Moon-Beehive: 3.3° S
     7  Su   2:33 pm  Moon-Mercury: 3.5° S
     8  Mo   4:14 am  Jupiter-Aldebaran: 4.8° N
    12  Fr   4:12 am  Moon Apogee: 404400 km
    12  Fr   6:27 pm  Moon Descending Node
    13  Sa   6:49 pm  First Quarter
    13  Sa   9:48 pm  Moon-Spica: 1° S
    17  We   3:37 pm  Moon-Antares:  .2° S
    19  Fr   6:59 am  Moon South Dec.: 28.4° S
    20  Sa   3:35 pm  Mars-Pleiades: 4.8° S
    21  Su   6:17 am  Full Moon
    22  Mo   2:59 am  Mercury Elongation: 26.9° E
    24  We   1:43 am  Moon Perigee: 364900 km
    24  We   4:38 pm  Moon-Saturn:  .4° S
    24  We   9:40 pm  Mercury-Regulus: 2° S
    26  Fr   1:33 am  Moon Ascending Node
    27  Sa   5:44 pm  Delta Aquarid Shower: ZHR = 20
    27  Sa  10:52 pm  Last Quarter
    29  Mo   5:13 pm  Moon-Pleiades:  .1° N
Aug  1  Th            Venus: 15.9° E

All event times are given for UTC-4:00 Eastern Daylight Saving Time thereafter.

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.

Note that the site is now kept up for archival purposes. Fred Espenak retired from NASA several years ago and has his own site, AstroPixels, which contain the same information: http://astropixels.com/almanac/almanac.html. However it uses standard time all year.

Sun and Moon Rising and Setting Events

LU             Ephemeris of Sky Events for Interlochen/TC
July, 2024 Local time zone: EDT
+-----------------------------------------------------------------------+
| DATE | SUN SUN DAYLIGHT| TWILIGHT* |MOON RISE OR ILLUM |
| | RISE SET HOURS | END START |PHASE SET** TIME FRACTN|
+=======================================================================+
|Mon 1| 06:01a 09:31p 15:30 | 10:57p 04:36a | Rise 02:50a 18%|
|Tue 2| 06:02a 09:31p 15:29 | 10:56p 04:36a | Rise 03:26a 10%|
|Wed 3| 06:02a 09:31p 15:28 | 10:56p 04:37a | Rise 04:13a 5%|
|Thu 4| 06:03a 09:31p 15:27 | 10:55p 04:38a | Rise 05:10a 1%|
|Fri 5| 06:03a 09:30p 15:26 | 10:55p 04:39a |New Set 09:59p 0%|
|Sat 6| 06:04a 09:30p 15:25 | 10:54p 04:40a | Set 10:39p 1%|
+------+-----------------------+----------------+-----------------------+
|Sun 7| 06:05a 09:29p 15:24 | 10:53p 04:41a | Set 11:10p 5%|
|Mon 8| 06:06a 09:29p 15:23 | 10:53p 04:42a | Set 11:34p 9%|
|Tue 9| 06:06a 09:29p 15:22 | 10:52p 04:43a | Set 11:53p 16%|
|Wed 10| 06:07a 09:28p 15:20 | 10:51p 04:44a | Set 12:10a 23%|
|Thu 11| 06:08a 09:27p 15:19 | 10:50p 04:45a | Set 12:26a 32%|
|Fri 12| 06:09a 09:27p 15:17 | 10:49p 04:46a | Set 12:42a 41%|
|Sat 13| 06:10a 09:26p 15:16 | 10:48p 04:47a |F Qtr Set 12:58a 50%|
+------+-----------------------+----------------+-----------------------+
|Sun 14| 06:11a 09:25p 15:14 | 10:47p 04:49a | Set 01:17a 60%|
|Mon 15| 06:12a 09:25p 15:13 | 10:46p 04:50a | Set 01:40a 69%|
|Tue 16| 06:12a 09:24p 15:11 | 10:45p 04:51a | Set 02:10a 78%|
|Wed 17| 06:13a 09:23p 15:09 | 10:44p 04:52a | Set 02:49a 86%|
|Thu 18| 06:14a 09:22p 15:07 | 10:43p 04:54a | Set 03:40a 92%|
|Fri 19| 06:15a 09:21p 15:06 | 10:41p 04:55a | Set 04:45a 97%|
|Sat 20| 06:16a 09:21p 15:04 | 10:40p 04:56a | Set 06:01a 100%|
+------+-----------------------+----------------+-----------------------+
|Sun 21| 06:17a 09:20p 15:02 | 10:39p 04:58a |Full Rise 10:07p 99%|
|Mon 22| 06:18a 09:19p 15:00 | 10:38p 04:59a | Rise 10:37p 97%|
|Tue 23| 06:19a 09:18p 14:58 | 10:36p 05:00a | Rise 11:01p 91%|
|Wed 24| 06:20a 09:17p 14:56 | 10:35p 05:02a | Rise 11:23p 83%|
|Thu 25| 06:21a 09:16p 14:54 | 10:33p 05:03a | Rise 11:43p 74%|
|Fri 26| 06:23a 09:14p 14:51 | 10:32p 05:05a | Rise 12:03a 63%|
|Sat 27| 06:24a 09:13p 14:49 | 10:30p 05:06a |L Qtr Rise 12:26a 51%|
+------+-----------------------+----------------+-----------------------+
|Sun 28| 06:25a 09:12p 14:47 | 10:29p 05:08a | Rise 12:52a 40%|
|Mon 29| 06:26a 09:11p 14:45 | 10:27p 05:09a | Rise 01:26a 30%|
|Tue 30| 06:27a 09:10p 14:42 | 10:26p 05:11a | Rise 02:08a 20%|
|Wed 31| 06:28a 09:09p 14:40 | 10:24p 05:12a | Rise 03:01a 12%|
+-----------------------------------------------------------------------+
* Nautical Twilight
** Moonrise or moonset, whichever occurs between sunset and sunrise

Generated using my LookingUp for DOS app.

Ephemeris: 06/28/2024 – Solar viewing at Sleeping Bear Dunes tomorrow

June 28, 2024 Comments off

This is Ephemeris for Friday, 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, at last quarter today, will rise at 1:37 tomorrow morning.

Tomorrow, Saturday, June 29th there will be solar viewing at the Sleeping Bear Dunes National Lakeshore, at the Dune Climb from 3 to 6 PM. Park Rangers will be joined by members of the Grand Traverse Astronomical Society with their specially filtered telescopes to view the Sun safely. This is a period of great solar activity. Remember the Aurora Borealis of a few weeks ago. Solar filtered telescopes will safely view the surface of the sun, called the photosphere and sunspots, while the society also has two special solar telescopes with which to view the layer of gas above the surface called the chromosphere and prominences which look like flames coming off the chromosphere. This is one of two solar observing opportunities this summer.

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 white light Sun
The white light Sun as of Thursday gives us a preview of what it will look like on Saturday. Most solar telescopes we use will give a mirror image. The sunspots will move and change from Thursday’s appearance, seen here. White light filters generally give the Sun an orange hue. It’s really white. Credit: NASA/Solar Dynamics Observatory.
The Sun in the light of hydrogen
The Sun in the light of hydrogen taken late Thursday our time (11:16 pm). The color is truly red in this photograph and in our hydrogen alpha solar telescopes. The alpha radiation of hydrogen is in the red part of the spectrum. What we are looking at is the chromosphere was a which is a layer of gas above the photosphere, which is the bright ball of the Sun that we see through white light telescopes. It gives us a very different view of the Sun which is much less smooth and with a lot of detail. The dark clouds over the photosphere are called filaments and if they were at the edge of the Sun we’d see them as bright features called prominences, though dimmer than the chromosphere which is why they appear dark when silhouetted over the chromosphere. The bright areas are called pledges and are magnetically active areas as are the sunspots. These are areas which may produce sunspots later. The chromosphere changes a lot more than the white light Sun and its sunspots. Credit: NISP / Learmouth, Australia.

Ephemeris: 06/27/2024 – Why do astronomers think a nova will appear this year?

June 27, 2024 Comments off

This is Ephemeris for Thursday, 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 last quarter, will rise at 1:18 tomorrow morning.

Our expected nova this year, T Coronae Borealis, is expected by some astronomers to erupt sometime in September give or take, but nobody knows for sure. The last eruption was seen in 1946. And if the average time between outbursts is 80 years, it seems to be two years early this time. In 1946 there were observations showing that there were some precursor effects going on before the eruption, and those have been noticed this time too, which is which why we assume that the nova will occur this year. Stars that vary in brightness are denoted in a constellation by a letter starting with R through Z, then RR, RS, etcetera through ZZ. After that it’s V and a number plus the constellation name or abbreviation.

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

T Coronae Borealis Finder Chart
This animated GIF shows the constellations of Hercules, Corona Borealis and Boötes from left to right. Flashing on and off is T Coronae Borealis (T CrB). It is shown at its approximate maximum brightness, about the same as Alphecca (spelled Alphekka here). Created using Stellarium and GIMP.

Ephemeris: 06/26/2024 – Where are the naked-eye planets this week?

June 26, 2024 Comments off

This is Bob Moler with Ephemeris for Wednesday, June 26th. 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, 2 days before last quarter, will rise at 12:58 tomorrow morning.

Let’s find out where the naked-eye planets have wandered off to this week. Venus and Mercury are too close to the direction of the Sun to be seen. Both are on the evening side of the Sun, but lost in its glare. Venus will appear in the evening sky next month. By 5:15 tomorrow morning, or about 45 minutes before sunrise, Saturn will be in the southeast just above and left of the Moon, and Mars will be lower in the east, and Jupiter will be very low in the east-northeast. Saturn will be a bit dimmer this year and next due to its rings being nearly edge on to us and not reflecting as much light. Saturn will rise at 1:15 am, Mars at 3:07 am, and Jupiter at 4:19 am.

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 Moon as it might appear in binoculars or a small telescope at 5 AM tomorrow morning, June 27th 2024. Selected features are labeled. Created using Stellarium, LibreOffice Draw, and GIMP.
The Moon, Saturn, Mars and Jupiter as they might be seen low in the east and southeastern sky at 5:15 AM, or about 45 minutes before sunrise, tomorrow morning June 27, 2024. Saturn will rise at 1:03 AM, Mars at 2:59 AM, and Jupiter at 4:09 AM. Click or tap on the image to enlarge it. Created using Stellarium.
Telescopic Saturn and Jupiter (north up) as they would be seen in a small telescope at 5 AM June 27th 2024 with the same magnification. Apparent diameters: Saturn 17.8″, its rings 41.4″; Mars, too small to be represented here, is 5.3″; Jupiter 33.5″. Note the ” means seconds of arc, or 1/3600th of a degree. 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 June 26, 2023. The night ends on the left with sunrise on the 27th. Click or tap on the image to enlarge it. Created using my LookingUp app and GIMP.
This is an ephemeris of the Sun Moon and naked eye planet positions for today and tomorrow, June 26th and 27th 2024. Some of the columns are self-explanatory, others 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. Dec is declination which is the north-south position of the object on the celestial sphere. 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 by my Ephemeris Helper app.

Ephemeris: 06/25/2024 – Three kinds of novas

June 25, 2024 Comments off

This is Ephemeris for Tuesday, June 25th. Today the Sun will be up for 15 hours and 33 minutes, setting at 9:32, and it will rise tomorrow at 5:58. The Moon, 3 days before last quarter, will rise at 12:35 tomorrow morning.

As I mentioned yesterday we’re expecting a nova or bright star that we expect to appear sometime this year, maybe in September according to some astronomers. A nova is a rapid brightening of a star due to some cataclysmic event happening to it. There are three kinds that we actually know of. A nova, which is what we’re expecting; a supernova, an explosion maybe a million times greater; and the recently discovered kilonova when two neutron stars collide, which is a thousand or so times brighter than an ordinary nova. A nova and one kind of supernova (Type 1) involve a binary star system which contains a white dwarf star near the end of its life close enough to a larger star to siphon off material. At some point enough has built up and an explosion occurs.

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 second type of Supernova is caused when a supermassive star’s core collapses when it’s made of iron and tries to fuse it into heaver elements. That process takes energy rather than producing it. Oops! The star collapses on itself, and… Kablooey!

Nova in a binary system


A red giant star and white dwarf orbit each other in this animation of a nova similar to T Coronae Borealis. The red giant is a large sphere in shades of red, orange, and white, with the side facing the white dwarf the lightest shades. The white dwarf is hidden in a bright glow of white and yellows, which represent an accretion disk around the star. A stream of material, shown as a diffuse cloud of red, flows from the red giant to the white dwarf. When the red giant moves behind the white dwarf, a nova explosion on the white dwarf ignites, creating a ball of ejected nova material shown in pale orange. After the fog of material clears, a small white spot remains, indicating that the white dwarf has survived the explosion. NASA/Goddard Space Flight Center
.

Ephemeris: 06/24/2024 – Waiting for a bright nova*

June 24, 2024 Comments off

This is Ephemeris for Monday, June 24th. Today the Sun will be up for 15 hours and 34 minutes, setting at 9:32, and it will rise tomorrow at 5:58. The Moon, 3 days past full, will rise at 12:09 tomorrow morning.

The small constellation of Corona Borealis, or Northern Crown appears about a third of the way between the bright star Arcturus, high in the south and the star Vega in the east. It is a small semicircle of stars with the brighter star called Alphecca near the center of the arc of stars. Sometime this year, we hope, another bright star will appear there. A nova of a dim star brightening about 1,600 times normal near that circle of stars. It has done it before. It has the designation of T Coronae Borealis (T CrB for short), and is a recurrent nova of a white dwarf star that suffers an explosion about once every 80 years. So this year we need to be looking out for that stellar explosion, which will be bright for only a few days, so one must be vigilant to spot 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.

* The word ‘nova’ comes from the Latin Nova Stella, meaning New Star.

Addendum

Finding Corona Borealis
Putting Corona Borealis in context with the Big Dipper, to the upper right, looking overhead while facing south, at 11 pm in late June. Created using Stellarium and GIMP.
Showing the location of T Coronae Borealis
This animated GIF shows the constellations of Hercules, Corona Borealis and Boötes from left to right. Flashing on and off is T Coronae Borealis (T CrB). It is shown at its approximate maximum brightness, about the same as Alphecca (spelled Alphekka here). Created using Stellarium and GIMP.
Light curve for Nova Cygni 1975 (V1500 Cyg) which burst forth in the constellation of Cygnus the Swan in August of 1975, just two months after the beginning of the Ephemeris program. There hasn’t been a brighter one since. Notice the initial sharp rise and initial decline. Magnitudes (Mag on the vertical axis) work like golf scores or prizes, the brighter the star the lower the magnitude number. The dimmest star visible to the naked eye is about 6th magnitude. You can blame Hipparchus for that numbering scheme.

NASA has post about T CrB here: https://www.nasa.gov/centers-and-facilities/marshall/nasa-global-astronomers-await-rare-nova-explosion/

Ephemeris: 06/21/2024 – Saturn’s rings are almost edge-on this year

June 21, 2024 Comments off

This is Ephemeris for Friday, June 21st. Today the Sun will be up for 15 hours and 34 minutes, setting at 9:32, and it will rise tomorrow at 5:57. The Moon, at full today, will rise at 9:57 this evening.

Saturn’s rings change their aspect or their tilt to us over a period of nearly 30 years, the time it takes Saturn to orbit the Sun. Saturn has an axial tilt like the Earth does in its case it is 27° compared to the Earth’s 23 1/2 degrees. So as Saturn moves around the Sun and us we see those rings at different tilts to us. Currently, the angle of the rings to us is nearing zero degrees, meaning that they are going edge on to us. And being perhaps less than 100 meters thick, they will disappear entirely in telescopes from the Earth. That will happen on March 23rd next year. However, they will not go edge on to the Sun until May 6th. So between March 23rd and May 6th we will be we will be looking at the unlit or dark side of the rings. Since we’re not at in line with the Sun and Saturn, the Sun will still be illuminating the rings slightly, but we will be looking at the dark side of the rings.

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

Saturn's rings change.
How the appearance of the rings change as Saturn orbits the Sun. Credit: NASA Hubble.

Ephemeris: 06/20/2024 – Summer starts this afternoon

June 20, 2024 Comments off

This is Ephemeris for Thursday, June 20th. Today the Sun will be up for 15 hours and 34 minutes, setting at 9:31, and it will rise tomorrow at 5:57. The Moon, 1 day before full, will set at 4:59 tomorrow morning.

Well, this is it, the summer solstice! Summer will begin at 4:51 this afternoon. In the Southern Hemisphere the season of winter will begin, and the South Pole of the Earth in the middle of its six months of darkness. Maybe we should call it the June solstice, because winter also begins in the Southern Hemisphere. The north above 66 ½ degrees north latitude is the land of the midnight Sun. Over summer that line will creep northward as the Sun heads southward. The seasons are caused by the tilt of the Earth’s axis, not by the Earth’s change in distance from the Sun. In fact, we are approaching our farthest distance from the Sun, of about 94.5 million miles (152 million kilometers) on July 5th, called aphelion. The greater than normal distance makes summer the longest season at 93.7 days, winter being the shortest at 89 days. The Sun will be at its highest, of just under 69 degrees altitude at 1:44 pm for the Interlochen/Traverse City area, and about a degree lower than that in the Straits area, though their daylight hours will be 12 minutes longer.

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

Solstices
Comparing the Sun’s path at the summer and winter solstices in Traverse City, MI, US. This is a stereographic representation of the whole sky which distorts the sky and magnifies the size of the Sun’s path near the horizon. Created using my LookingUp app and GIMP.