Archive
09/27/2022 – Ephemeris – Finding the constellation of Perseus the hero
This is Ephemeris for Tuesday, September 27th. Today the Sun will be up for 11 hours and 54 minutes, setting at 7:30, and it will rise tomorrow at 7:37. The Moon, 2 days past new, will set at 8:28 this evening.
Close to the horizon, but rising in the northeast in the evening, is the constellation of Perseus the Greek hero, holding as his prize the severed head of Medusa. To me, the stars don’t seem to match the figure in the stars. It’s either the Greek letter pi (π) tilted to the left or the cartoon roadrunner running up the sky. Perseus’ brightest star is Mirfak in the middle of the top of the letter π, or back of the roadrunner. Using a pair of binoculars to look towards Mirfak, one can see many more stars, just below naked eye visibility near it. It’s a very loose star cluster called the Alpha (α) Persei Association, α Persei being a catalog designation for Mirfak. And Mirfak is actually in the association. Unlike some bright stars, who are just foreground stars.
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
For my take on the mythology featuring Perseus, see The Great Star Story of Autumn. It’s way too long for my short radio program. For Hollywood’s treatment of the story, see Clash of the Titans.
Perseus finder using the animated GIF to show the star field, constellation lines and names, and Perseus as art. Cassiopeia is included as a means to find the dimmer Perseus below it on autumn evenings. Algol, another important star and the second-brightest star of Perseus, is also labeled. I normally cover it around Halloween, but if you can’t wait, type Algol in the search box at the upper right. Created using Stellarium, LibreOffice Draw, and GIMP.
The Alpha Persei Association. The brightest star is Mirfak (Alpha Persei). This is a small section of a photograph taken February 18, 2017, Canon EOS Rebel T5, 121 seconds, f/3.5, 18 mm fl., ISO 3200. Credit Bob Moler.
09/20/2022 – Ephemeris – Finding the constellation of Pegasus the flying horse
This is Ephemeris for Tuesday, September 20th. Today the Sun will be up for 12 hours and 16 minutes, setting at 7:43, and it will rise tomorrow at 7:28. The Moon, 3 days past last quarter, will rise at 2:33 tomorrow morning.
Rising about a third of the way up the sky in the east as it gets dark around 9 pm can be found one of the great autumn constellations: Pegasus the flying horse of Greek myth. Its most visible feature is a large square of four stars, now standing on one corner. This feature, called the Great Square of Pegasus, represents the front part of the horse’s body. The horse is quite aerobatic, because it is seen flying upside down. Remembering that fact, the neck and head is a bent line of stars emanating from the right corner star of the square. Its front legs can be seen in a gallop extending to the upper right from the top star of the square. From the left star extend, not hind legs but the constellation of Andromeda, the princess rescued with the help of Pegasus.
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
Pegasus & Andromeda animated finder chart for 9 pm in mid-September. To the upper left are most of the stars of the “W” shape of Cassiopeia the queen, Andromeda’s mother. Created using Stellarium and GIMP.
Pegasus, Andromeda and Cassiopeia plus other constellations are characters in the great star story of autumn which I relate here.
09/19/2022 – Ephemeris – Finding the constellation Cepheus
This is Ephemeris for Monday, September 19th. Today the Sun will be up for 12 hours and 19 minutes, setting at 7:45, and it will rise tomorrow at 7:27. The Moon, 2 days past last quarter, will rise at 1:30 tomorrow morning.
There’s a faint constellation in the northeast above the W shaped constellation of Cassiopeia. It’s a nearly upside down church steeple of a constellation called Cepheus the king, and husband of queen Cassiopeia. Cepheus’ claim to modern astronomical fame is that one of its stars, Delta (δ) Cephei, is the archetype for the important Cepheid variable stars. Delta is the bottom most of a trio of stars at the right corner of the constellation. In the early 20th century, Henrietta Leavitt discovered that Cepheids in the nearby galaxy the Large Magellanic Cloud varied in brightness with a period that was related to their average brightness. This meant that Cepheids could be used as standard candles to measure the great distances to other galaxies.
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
Cassiopeia and Cepheus finder animation looking in the northeast at 9 pm or about an hour after sunset in mid-September. Also labeled is Delta (δ) Cephei. Created using Stellarium and GIMP.
Light Curve of Delta Cephei. The pulsation period is 5.367 days. Note the Magnitude vertical axis, the lower the magnitude the brighter the star is. Blame that on the Greek astronomer Hipparchus, 2nd century BC. It’s like golf scores; the lower the score, the better the golfer, and for magnitudes, the brighter the star. Credit: Thomas K Vbg – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=13887639.
09/16/2022 – Ephemeris – Alberio: a double star that showcases star colors
This is Ephemeris for Friday, September 16th. Today the Sun will be up for 12 hours and 28 minutes, setting at 7:51, and it will rise tomorrow at 7:24. The Moon, 1 day before last quarter, will rise at 11:03 this evening.
Alberio is the name given to the star that is in the head of the constellation of Cygnus the swan, which is high in the east these evenings. It is also at the foot of the asterism or informal constellation of the Northern Cross. To the naked eye Albireo looks like a single star, however even in small telescopes its true nature is revealed. It’s a double star whose individual star colors are strikingly different Its brightest star is yellow, and the dimmer star is blue. While star colors are subtle, these two, due to their apparent closeness, make an obvious color contrast. Unlike what your interior decorator says: In stars, blue is hot, yellow, orange and red are cool. The two stars are too far apart to be considered a binary star system, but appear to move together in space. It is what is called an optical double, though they’re both around 430 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
Animated Albireo finder chart. Albireo is located in the head of Cygnus the swan, or at the base of the Northern Cross. Tagged stars are, beside Albireo, the stars of the Summer Triangle: Deneb, Vega and Altair plus the star at the junction of the upright and crosspiece of the cross, Sadr. Created using Stellarium.
Albireo, captured at high magnification by the staff of the Smithsonian Institution. Informally, at star parties, I call it the U of M Star because it displays the University of Michigan’s Maize and Blue colors.
A note about star colors
The color of a star is dependent on its surface temperature. The term surface is a misnomer, because stars do not have a surface, at least not a solid one, being gaseous in nature. The only exception I can think is a neutron star, which is packed with neutrons. We consider the Sun’s photosphere synonymous with “surface”. The photosphere of the Sun is where the energy transport from the core changes from convection to radiation. The color of the Sun is a measure of the temperature of the photosphere. The color sequence from the coolest to the hottest is: red, orange, yellow, white and blue. The light emitted by a star is not a pure color, but a distribution of colors, whose peak shifts along that range. There is much more to tell, but that’s beyond the scope of this post.
09/15/2022 – Ephemeris – Finding Cassiopeia this time of year
This is Ephemeris for Thursday, September 15th. Today the Sun will be up for 12 hours and 31 minutes, setting at 7:53, and it will rise tomorrow at 7:22. The Moon, 2 days before last quarter, will rise at 10:30 this evening.
In the northeastern sky is a letter W shaped constellation of Cassiopeia, the queen of Greek myth. I can’t say Cassiopeia is rising in the northeast, because it never sets for us in northern Michigan. This time of year it skirts above the northern horizon during the daytime. One of Cassiopeia’s claims to historical astronomical fame is that it’s the location of Tycho’s Star, a supernova discovered in 1572 by Danish astronomer Tycho Brahe, the last of the great astronomers prior to the invention of the telescope. Tycho was able to prove that the temporary phenomenon was actually a star in the heavens, disproving the Greek notion that the heavens were changeless and perfect. The Chinese had already known that, calling them Guest Stars.
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
Cassiopeia finder animation for 10 pm tonight, September 15th. One cannot miss the distinctive W. Created using Stellarium.
Tycho’s Supernova 1574A, as simulated in Stellarium for mid-November 1572.
Tycho’s Supernova remnant, seen in x-rays by the orbiting Chandra X-ray Observatory. Credit: NASA / Chandra
09/08/2022 – Ephemeris – We are going to have an early Harvest Moon this year
This is Bob Moler with Ephemeris for Thursday, September 8th. Today the Sun will be up for 12 hours and 53 minutes, setting at 8:06, and it will rise tomorrow at 7:14. The Moon, 2 days before full, will set at 5:54 tomorrow morning.
We are going to have an early Harvest Moon this year, on the early morning of Saturday the 10th, this Saturday coming up. The Harvest Moon is the closest full moon to the autumnal equinox, which is on the 22nd. The earliest a Harvest Moon can fall is on the 8th of September. The reason that the Harvest Moon is so famous is that at sunset the Moon’s path, in the sky, is shallow to the horizon. So it rises much less than its average 50 minutes later each night. This effectively lengthens the amount of useful twilight, allowing more time to harvest the crops. It compensated for the rapid retreat of the daylight hours this time of year. It’s not so important now, but back before electric lights it definitely was.
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 Harvest Moon rising as seen in Stellarium. The planetarium program Stellarium, which I use a lot, also colors the rising and setting Moon and Sun. It also reproduces the effect of atmospheric refraction, which makes objects close to the horizon look higher than they are. Thus, extended objects close to the horizon appear squashed a bit vertically.
The Harvest Moon effect is a phenomenon where the Moon’s nightly advance in rising times become much shorter than the average 50 minutes. This has the effect of extending the bright part of twilight for up to a week near the Harvest Moon. Complicating effects this year are the fact that the Harvest Moon is a supermoon, being a bit brighter than normal, and also moving faster than normal, negating the harvest moon effect somewhat. The Moon’s perigee was on the 7th, so the Moon is slowing down*, which shows in the delay numbers. Also helping to shorten the delay is that the path of the Moon is a bit shallower than the ecliptic. The Moon is south of the ecliptic, heading northward to its ascending node.
The Moon moves fastest in its orbit at perigee, and its slowest at apogee, at its farthest from the Earth.
08/23/2022 – Ephemeris – A king’s shield in the sky
This is Bob Moler with Ephemeris for Tuesday, August 23rd. Today the Sun will be up for 13 hours and 40 minutes, setting at 8:35, and it will rise tomorrow at 6:55. The Moon, halfway from last quarter to new, will rise at 3:42 tomorrow morning.
In the southern sky between the Teapot of Sagittarius below and Aquila the Eagle with its southernmost star of the Summer Triangle lies Scutum the shield of John Sobieski, the Polish king who stopped the advance of the Turks at Kalenberg in 1683. The Polish half of me is very proud. Scutum is one of two official constellations which are related to real persons. The other one is Coma Berenices, a hank of the Egyptian Queen Berenice’s hair. However, the stars here are so dim and embedded in the glow of the Milky Way as to be nearly impossible to discern. Scutum lies in one of the richest portions of the Milky Way, wonderful to scan with binoculars and telescopes for star clusters and nebulae or clouds of dust and gas.
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
I think of Scutum as an area of the Milky Way between Aquila and Sagittarius. Created using Stellarium and GIMP.
08/18/2022 – Ephemeris – The Great Rift
This is Ephemeris for Thursday, August 18th. Today the Sun will be up for 13 hours and 54 minutes, setting at 8:43, and it will rise tomorrow at 6:49. The Moon, 1 day before last quarter, will rise at 12:02 tomorrow morning.
High overhead, the Milky Way is seen passing through the Summer Triangle of three bright stars. Here we find the Milky Way splits into two sections. The split starts in the constellation of Cygnus the Swan or Northern Cross very high in the east. The western part of the Milky Way ends southwest of Aquila the eagle. This dark dividing feature is called the Great Rift. Despite the lack of stars seen there, it doesn’t mean that there are fewer stars there than in the brighter patches of the Milky Way. The rift is a great dark cloud that obscures the light of the stars behind it. Sometimes binoculars can be used to find the edges of the clouds of the rift, as star numbers drop off suddenly. This is especially easily seen in Aquila.
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 Great Rift finder animation as seen in the Summer Triangle, also showing the constellations of Cygnus the swan and the northern part of Aquila the Eagle. This image a stack of 5 30 second exposures taken the morning of the Perseid meteor shower the is year in a vain attempt to capture some meteors.
Let’s search for the naked-eye planets for this week
This is Bob Moler with Ephemeris for Wednesday, August 17th. Today the Sun will be up for 13 hours and 57 minutes, setting at 8:45, and it will rise tomorrow at 6:48. The Moon, 2 days before last quarter, will rise at 11:37 this evening.
Let’s search for the naked-eye planets for this week. Two of the naked-eye planets are in the evening sky: Mercury sets too close to the Sun to be seen in the evening, but as it gets darker, Saturn can be seen low in the southeast. At 6 am tomorrow, the planets will be spread out from brilliant Venus low in the east-northeast to Saturn in the west-southwest. Mars will be a lot higher than Venus in the southeast. Jupiter is farther to the right in the south-southwest. Mars is dimmer than Jupiter, but is slowly getting brighter as the Earth creeps up on it. Saturn ends the line of planets lower than Venus, if it’s visible at all, in the west-southwest, only 5 degrees above a sea, or Lake Michigan horizon.
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
An animation showing Saturn at 10 pm, along with three zodiacal constellations, with and without labels, just after the end of nautical twilight tonight at 10 pm, August 17, 2022. Click on the image to enlarge it. Created using Stellarium and GIMP.
The Moon as it might appear at midnight tonight, August 18, 2022. Created using Stellarium.
Views of Saturn, Jupiter, and Venus (north up) as they would be seen in a small telescope, with the same magnification. The times vary for each planet. Jupiter is shown twice, at midnight and 6 am, since its moons, especially Io and Europa, move rapidly. I do not show planets less than 10 seconds of arc in diameter, so Mars doesn’t show up yet. It will soon. Apparent diameters: Saturn 18.76″, its rings 43.70″; Jupiter 47.33″. Mars 9.04″, 84.7% illuminated; Venus 10.31″, 94.3% illuminated. 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 August 17, 2022. The night ends on the left with sunrise on the 18th. Click on the image to enlarge it. Created using my LookingUp program.
08/16/2022 – Ephemeris – Scanning Sagittarius with binoculars
This is Bob Moler with Ephemeris for Tuesday, August 16th. Today the Sun will be up for 14 hours to the minute, setting at 8:46, and it will rise tomorrow at 6:47. The Moon, 3 days before last quarter, will rise at 11:15 this evening.
The Moon has left the evening sky, so let’s take another look at the constellation of Sagittarius. Its bright stars make a follow the dots image of a stout little teapot. In, around and above the teapot is a wealth of nebulae, which are clouds of gas and dust and clusters of stars. Stars are born in bunches from a cloud of gas. When enough stars are born, their stellar winds blow away the nebulosity leaving a star cluster. Use a pair of binoculars or a very low power telescope and just wander around and above the teapot, including and especially the spout on the right side. In binoculars, star clusters appear fuzzy like nebulae, however a small telescope with magnification of 20 times should resolve most of them.
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
Sagittarius in a short time exposure with added annotations. The “M” designations are objects in Charles Messier’s catalog created in the latter half of the 18th century. LSSC is the Large Sagittarius Star Cloud, SSSC is the Small Sagittarius Star Cloud. Labels are to the right of the objects they name. Credit Bob Moler.
This is the short radio program version of the August 8, 2022, Ephemeris Extra post Wandering through Sagittarius
