10/29/2021 – Ephemeris – Venus is at its greatest separation east from the Sun today

This is Ephemeris for Friday, October 29th. Today the Sun will be up for 10 hours and 18 minutes, setting at 6:35, and it will rise tomorrow at 8:18. The Moon, 1 day past last quarter, will rise at 1:39 tomorrow morning.

Tonight, Venus will be at its greatest separation east of the Sun of 47 angular degrees. Having an orbit inside the Earth’s orbit, Venus never strays more than a 47-degree angle from the Sun. It has been moving away from around behind the Sun to its present position since March 26th. That’s 217 days. And now it will take only 72 days to head back to pass between the Earth and the Sun in inferior conjunction and leave the evening sky on January 9th. For this next 70 or so days, Venus will look great in telescopes. It will get larger as it approaches us and become a dazzling crescent in telescopes. Toward the latter half of December, the tiny crescent can even be made out in binoculars. It is the very best time to view Venus in a telescope.

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 at greatest elongation, seen at 7 pm tonight, October 29, 2021. Note how shallow the orbit is compared with Mercury’s orbit was on Monday’s (10/25/2021) post of Mercury’s greatest western elongation as seen in the morning. Created using Stellarium.

10/28/2021 – Ephemeris – The spookiest star in the sky

This is Ephemeris for Thursday, October 28th. Today the Sun will be up for 10 hours and 21 minutes, setting at 6:36, and it will rise tomorrow at 8:17. The Moon, at last quarter today, will rise at 12:31 tomorrow morning.

We are getting down to the spookiest time of the year, with Halloween on Sunday, so it’s time to talk about the spookiest star in the sky, Algol the Ghoul or Demon Star. It’s in the constellation of Perseus the hero, now rising in the northeastern sky. The constellation itself looks like the Greek letter pi, or like the cartoon Roadrunner with its long legs. Algol is the second brightest star in the constellation, near the Roadrunner’s leading foot. That’s where the eye of the severed head of Medusa, that Perseus is carrying. It’s still winking, once every 2 days and 21 hours*. Tonight it will be in the deepest part of its wink at 8:43 pm. It will take about three hours to recover its usual brightness. I recall that the ancient Chinese weren’t fond of that star either.

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.

* More specifically, 2 days, 20 hours, 49 minutes on average and altered by Earth’s changing distance from the star due to its orbit of the Sun.

Addendum

Algol Finder Animation for around 8 pm in the later part of October and early November (7 pm after the EST time change on the first Sunday in November). Created using Stellarium and GIMP.

Algol is an eclipsing binary star, where one star eclipses the other.

Animation of an eclipsing binary star like Algol. Credit: Wikimedia Commons h/t Earth and Sky

10/27/2021 – Ephemeris – Let’s search for the naked-eye planets for this week

This is Bob Moler with Ephemeris for Wednesday, October 27th. Today the Sun will be up for 10 hours and 23 minutes, setting at 6:38, and it will rise tomorrow at 8:15. The Moon, 1 day before last quarter, will rise at 11:27 this evening.

Let’s search for the naked-eye planets for this week. Venus should be visible in the southwestern evening twilight by 7 tonight. It will set at 8:43 pm. By 7:15 pm, Jupiter will be spotted in the south-southeastern sky. Jupiter should be easy to spot at that hour. Saturn will be dimmer, and to its right. They will be visible for a while after midnight in the southwest, with Saturn setting first at 12:37 am, and Jupiter following at 1:57. Saturn’s rings are a beautiful sight in a telescope of even modest power, but the planet will appear tiny. In the morning sky, Mercury will be visible and low in the east-southeast for most of the 7 am hour. All four of Jupiter’s brightest moons will be visible in binoculars early in the evening 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 will appear low in the southwest by 7 pm tonight, October 27, 2021. Created using Stellarium.

Jupiter and Saturn in evening twilight at 7:15 pm tonight, October 27, 2021. Created using Stellarium.

The Moon as it might appear in binoculars or a small telescope tomorrow morning, October 28, 2021. Created using Stellarium.

Mercury in morning twilight finder for 7:30 am tomorrow, October 28, 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 9 pm, October 27, 2021. Apparent diameters: Venus at 7 pm, 24.19″, 50.8% illuminated; Saturn 16.92″, its rings 39.41″; Jupiter, 42.87″. Mercury at 7:30 am on the 28th and not plotted, 6.47″, 64.9% illuminated. The Jovian moon Io will begin transiting the face of the planet at 9:20 pm. Its shadow will start to cross at 10:37 pm. Io’s transit will end at 11:37 pm. 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 27, 2021. The night ends on the left with sunrise on the 28th. Click on the image to enlarge it. Created using my LookingUp program.

10/26/2021 – Ephemeris – The bright star Capella is slowly ascending in the northeastern sky

This is Ephemeris for Tuesday, October 26th. Today the Sun will be up for 10 hours and 26 minutes, setting at 6:39, and it will rise tomorrow at 8:14. The Moon, 2 days before last quarter, will rise at 10:29 this evening.

The bright star that’s been hanging out fairly low in the northeastern sky in the evening lately is Capella, sometimes called the Goat Star. It’s at the top of a rather oddly shaped pentagon of stars that make up the constellation Auriga, the charioteer. A small, thin triangle of stars to Capella’s right is called the Kids*. Her kids. I’m not sure what a fellow is doing holding 4 goats while driving a chariot. Maybe that’s how he ended up in the sky. Capella itself consists of two yellow giant stars, about the same temperature as the Sun, but much larger. Capella is circumpolar for most of northern Michigan, meaning it never sets. It gets pretty low in the north on summer evenings.

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.

* I’ve always known them as the Kids. Stellarium calls them the Goatlings.

Addendum

Capella and Auriga, low in the northeastern sky. I left the Kids unannotated, but they are easy to find near Capella. An animation created using Stellarium and GIMP.

10/25/2021 – Ephemeris – Mercury is at its greatest separation west of the Sun of the season

This is Bob Moler with Ephemeris for Monday, October 25th. Today the Sun will be up for 10 hours and 29 minutes, setting at 6:41, and it will rise tomorrow at 8:13. The Moon, 3 days before last quarter, will rise at 9:38 this evening.

This morning at 12:59 am, the planet Mercury reached its greatest western elongation from the Sun. It reached an angle of 18.4 degrees west of the Sun. It will be visible for most of the 7 am hour low in the east southeastern sky. Mercury will be visible to the naked-eye for the next week or 10 days. The planet has quite an elliptical orbit. And it happens that in our favorable appearances of Mercury on fall mornings and spring evenings, we are seeing Mercury in the same part of its orbit. Which is near its perihelion, the closest part of its orbit of the Sun. Observers in the Southern Hemisphere see Mercury’s favorable elongations near aphelion, its farthest from the Sun, of around 28 degrees separation from Earth’s viewpoint.

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

Mercury, a day after greatest western elongation at 7:54 am, or 20 minutes before sunrise tomorrow morning, October 26, 2021. Also shown is its orbit, if we could see it. Mercury is virtually in the same position this morning. Created using Stellarium.

10/22/2021 – Ephemeris 3,001st post – Mercury is now visible in the morning before sunrise

This is Bob Moler with Ephemeris for Friday, October 22nd. Today the Sun will be up for 10 hours and 38 minutes, setting at 6:46, and it will rise tomorrow at 8:09. The Moon, 2 days past full, will rise at 7:53 this evening.

The planet Mercury is now visible on clear mornings, low in the east-southeastern sky after 7 am, and twilight gets too bright around 7:50 am. Tiny Mercury is the smallest planet, only 50% larger than our Moon. It looks a lot like our Moon, close up, all gray and covered in craters. But the resemblance is only skin deep. Before the Arecibo radio telescope could bounce radar pulses from the planet in the 1960s, we thought Mercury held one side pointed at the Sun and the other side eternally away. That wasn’t the case due to its elliptical orbit. It rotates in 59 days, two-thirds of its year of 88 days. This makes its solar day, noon to noon, last two of its years. The European BepiColombo mission to orbit Mercury just made its first pass of the planet.

Addendum

Mercury and its apparent orbit for 7:49 am tomorrow, October 23, 2021, two days before its greatest western elongation (separation from the Sun). Created using Stellarium.

BepiColombo takes a picture of Mercury on its first of 6 flybys, October 1st, before settling into orbit of the planet on December 5, 2025. BepiColombo is actually two spacecraft connected together, and parts of the other spacecraft will get into each other’s images until they separate. Credit: ESA/JAXA.

10/21/2021 – Ephemeris – Defending the planet

This is Ephemeris for Thursday, October 21st. Today the Sun will be up for 10 hours and 41 minutes, setting at 6:47, and it will rise tomorrow at 8:07. The Moon, 1 day past full, will rise at 7:29 this evening.

This is the 4th program in 8 days here on Ephemeris about asteroids. A possible collision of an asteroid or comet has been on our collective minds since the 20-some odd pieces of Comet Shoemaker-Levy 9 hit Jupiter in July 1994. In 2016 NASA established the Planetary Defense Coordination Office to manage its ongoing planetary defense efforts. Its mission is to provide early detection of potentially hazardous objects that can come within 5 million miles of the Earth’s orbit and a size large enough to cause significant damage. Asteroid sizes would be 30 to 50 meters in diameter, that’s 90 to 150 feet in diameter or larger. It will track and issue warnings of these objects when found. It will coordinate responses to any impact threat.

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

What the Planetary Defense Coordination Office does. Credit: NASA.

10/20/2021 – Ephemeris – Let’s search for the naked-eye planets for this week

This is Bob Moler with Ephemeris for Wednesday, October 20th. Today the Sun will be up for 10 hours and 44 minutes, setting at 6:49, and it will rise tomorrow at 8:06. The Moon, is full today, the Hunter’s Moon, and will rise at 7:07 this evening.

Let’s search for the naked-eye planets for this week. Venus should be visible in the southwestern evening twilight by 7:10 tonight. It will set at 8:44 pm. By 7:30 pm, Jupiter will be spotted in the south-southeastern sky. Jupiter should be easy to spot at that hour. Saturn will be dimmer, and to its right. They will be visible for a while after midnight in the southwest, with Saturn setting first at 1:04 am, and Jupiter following at 2:24. Saturn’s rings are a beautiful sight in a telescope of even modest power, but the planet will appear tiny. In the morning sky, Mercury will be visible and low in the east-southeast by 7:15 am. It will reach its greatest separation from the Sun in six days.

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 seen in twilight at 7:10 pm, about 20 minutes after sunset tonight, October 20, 2021. Created using Stellarium.

Full Hunter’s Moon rising at 7:11 this evening, October 20, 2021. Created using Stellarium.

Jupiter, Saturn and the Moon at 7:30, about 40 minutes after sunset tonight, October 20, 2021. Created using Stellarium.

Mercury and the star Arcturus in the morning twilight at 7:15 am, about 50 minutes before sunrise tomorrow morning, October 21, 2021. Don’t confuse the two. Click on the image to enlarge it. 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 20, 2021. Apparent diameters: Venus, 22.70″, 53.7% illuminated; Saturn 17.08″, its rings 39.80″; Jupiter, 43.68″. Mercury at 7:15 am on the 21st and not plotted, 7.68″, 38.1% illuminated. The two Jovian moons transiting the face of the planet are usually not visible, though their shadows can be spotted. 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 20, 2021. The night ends on the left with sunrise on the 21st. Click on the image to enlarge it. Created using my LookingUp program.

10/19/2021 – Ephemeris – Introducing the DART mission

This is Bob Moler with Ephemeris for Tuesday, October 19th. Today the Sun will be up for 10 hours and 47 minutes, setting at 6:50, and it will rise tomorrow at 8:05. The Moon, 1 day before full, will set at 7:54 tomorrow morning.

Last Saturday morning, the Lucy mission to Jupiter’s Trojan Asteroids was launched. These asteroids are forever locked in Jupiter’s orbit and will never be a hazard to the Earth. Next month, NASA will hopefully launch a mission to a much closer asteroid Didymos, which is considered a potentially hazardous asteroid. The asteroid has a diameter of a bit less than a half mile (780 meters). It also has a satellite named Dimorphos, which has acquired the nickname Didymoon, 520 feet (160 meters) in diameter. The mission called DART for Double Asteroid Redirection Test will see how the impact of a spacecraft hitting the small Didymoon will affect its orbit around the larger asteroid.

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 Double Asteroid Redirection Test (DART) mission is NASA’s contribution to the international Asteroid Impact & Deflection Assessment (AIDA) program to determine the effectiveness of a spacecraft kinetic impact of an asteroid in altering its orbit. Credit: NASA.

10/18/2021 – Ephemeris – Jupiter is stationary today

This is Ephemeris for Monday, October 18th. Today the Sun will be up for 10 hours and 50 minutes, setting at 6:52, and it will rise tomorrow at 8:03. The Moon, 2 days before full, will set at 6:49 tomorrow morning.

The planet Jupiter is stationary today after moving westward for the last four months, as the Earth passed it in our race around the Sun. And it will resume its normal prograde or eastward motion against the stars and constellations of the Zodiac. During this retrograde time it had seemed to move closer to Saturn. Now that it and Saturn are appearing to resume their eastward motion, Jupiter again will appear to open up the distance between them. The ancient Greeks had a devil of a time trying to model this behavior, because they started with two false premises. One, that the Earth was stationary in the center of the universe; and two, that the Sun, Moon, and planets moved in uniform circular motion because they were perfect.

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

Jupiter and Saturn’s apparent motions seen against the constellation of Capricornus in 2021, including their retrograde loops. Click on the image to enlarge it. The tracks begin on the right. By the end of 2021 neither planet recovers all the eastern progress they lost in their retrograde loops. Created using Cartes du Ciel (Sky Charts).