10/15/2021 – Ephemeris – NASA mission to Trojan Asteroids

This is Bob Moler with Ephemeris for Friday, October 15th. Today the Sun will be up for 10 hours and 59 minutes, setting at 6:57, and it will rise tomorrow at 7:59. The Moon, 3 days past first quarter, will set at 3:25 tomorrow morning.

Tomorrow opens up a window to launch a satellite named Lucy to the Trojan asteroids of Jupiter. Lucy is named for a fossil of a human ancestor discovered in Africa. After launch, Lucy will make two gravitational assist passes of the Earth to get up enough velocity to reach Jupiter’s orbit and pass near Five asteroids in the leading L4 cloud of Trojans. Its orbit will take it back to the Earth, where another gravitational assist will send it to a double asteroid in the trailing Trojan group. On its way out it will pass close to a tiny main belt asteroid DonaldJohanson, named after the discoverer of the Lucy fossil. The mission will last 12 years. After that, Lucy will orbit between the Earth’s orbit and each of the Trojan swarms in turn.

Lucy is scheduled to launch on an Atlas V on Saturday, 16 October 2021 at 09:34 UT (5:34 a.m. EDT) from Cape Canaveral. If the launch can’t take place then, they have something like 22 more days in which they can get it launched.

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 GIF showing Jupiter and Trojan Asteroids during one Jovian year, which repeats. Credit: Astronomical Institute of CAS/Petr Scheirich.

The Lucy spacecraft orbits as seen in the rotating frame of Jupiter’s orbit. Lucy’s orbits are actually ellipses. (I wish they would take the stars out, they should appear as circular trails centered on the Sun from Jupiter’s rotating frame.) Click on the image to enlarge it. Credit: Southwest Research Institute.

 

10/14/2021 – Ephemeris – What is a Trojan Asteroid?

This is Bob Moler with Ephemeris for Thursday, October 14th. Today the Sun will be up for 11 hours and 2 minutes, setting at 6:59, and it will rise tomorrow at 7:58. The Moon, 2 days past first quarter, will set at 2:13 tomorrow morning.

The Moon is near Jupiter tonight. On this Saturday, the 16th, the window opens up for the launch of NASA’s Lucy mission to Jupiter’s Trojan asteroids. More about the mission tomorrow, but what’s a Trojan asteroid? The Trojan asteroids are over 10,000 in number that lie in Jupiter’s orbit. One group, the Greeks, orbit around the L4 point 60 degrees ahead of Jupiter. The other, the Trojans orbit the L5 point 60 degrees behind Jupiter. Named after participants of the Trojan War, they are collectively named Trojan asteroids. Other planets, including the Earth, have Trojan asteroids. Trojan asteroids orbit the L4 and L5 gravitational equilibrium points in a planet’s orbit of the Sun, discovered by Joseph-Louis Lagrange in 1772. The first Trojan asteroid, was named Achilles after a warrior in the Trojan War, and was discovered in 1906. As new asteroids were found in these special positions, they were also given names from Homer’s Iliad.

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 two “camps” of Jupiter’s Trojan Asteroids. The Greek camp at L4 and the Trojan camp at L5. Credit Astronomy.com/Roen Kelly.

Other planets have Trojan Asteroids in their orbits. Earth has one, Mars has four, Uranus has two, Neptune has 28.  These are not the final numbers, just what has been found so far. Apparently, Venus has a temporary one. When the term Trojan Asteroids is used without reference to a planet, they are assumed to belong to Jupiter.

08/19/2021 – Ephemeris – Jupiter is at opposition today!

This is Ephemeris for Thursday, August 19th. Today the Sun will be up for 13 hours and 51 minutes, setting at 8:41, and it will rise tomorrow at 6:51. The Moon, 3 days before full, will set at 4:11 tomorrow morning.

Tonight, Jupiter will be at opposition. That’s a shortcut term for Jupiter being opposite the Sun in our sky. At that time, Jupiter rises at sunset and sets at sunrise. It is also at its closest to us. It also officially becomes an evening planet, available in the evening for those of us with daytime jobs. In even small telescopes, Jupiter shows two dark bands. There’s more, but those two are the most prominent. Its four largest moons will be visible before 9:50 pm tonight, after that the innermost of the four, Io, will start to cross the face of Jupiter. It will leave Ganymede on Jupiter’s east side. On the west side will be the moon Europa, and farther out, Callisto. At 12:08 am, Io will reappear on the west side of Jupiter, joining Europa and Callisto. The moons do put on a show.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hr). They may be different for your location.

Addendum

Jupiter’s Galilean moons at two times tonight, August 19th at 9:30 pm (01:30 on the 20th, UT) and 12:30 am (04:30 UT). From 9:50 pm to 12:08 am (01:50 – 04:08 UT), Io will pass in front of Jupiter and be practically invisible. Click on the image to enlarge it. Created using Cartes du Ciel (Sky Charts).

06/21/2021 – Ephemeris – A quick look at three of the naked-eye planets

This is Ephemeris for Monday, 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, 3 days before full, will set at 4:02 tomorrow morning.

I have a couple of pieces of planetary news. Venus will pass south of the star Pollux in Gemini tonight. That means in their current orientation, low on the west-northwestern horizon, that Pollux will appear above and right of the much brighter Venus. This may be visible by 10:30 pm. Venus will set tonight at 11:07. You’ll need a really low western horizon to see it. In the morning sky, Saturn is backtracking to the west slowly, and now Jupiter has stopped its eastward motion and is stationary today and will start its retrograde or westward motion. Both retrograde motions are caused by the Earth, which is in the process of passing these planets. We will pass Saturn August 2nd, and pass Jupiter August 19th. We call these events, oppositions.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4hr). They may be different for your location.

Addendum

Venus, Pollux and Mars in the evening twilight tonight at 10:30 pm. Venus and Pollux in evening twilight. Venus will be about 5 degrees above the sea or lake horizon at that time. Venus and Mars will cross their apparent paths and be in conjunction on July 13th. Click on the image to enlarge. Created using Stellarium.

Jupiter’s retrograde path, June 21, to October 20, 2021. The constellation lines in the lower right are for the eastern end of Capricornus. We pass Jupiter, officially called opposition from the Sun, on August 20th. The solid yellow line above Jupiter’s apparent path is the Ecliptic, the Sun’s apparent path in the sky. Click on the image to enlarge. Created using Cartes du Ciel (Sky Charts).

08/28/2020 – Ephemeris – Tonight Jupiter and the Moon will appear together in the sky

This is Ephemeris for Friday, August 28th. Today the Sun will be up for 13 hours and 24 minutes, setting at 8:25, and it will rise tomorrow at 7:02. The Moon, 3 days past first quarter, will set at 2:56 tomorrow morning.

Tonight at 9:33 pm the Moon will pass Jupiter in our skies. Jupiter will appear about 5 moon-widths above the Moon. It’s a good time to get out those binoculars or a small telescope to look at them. Jupiter will have its four brightest moons, two on each side. They are pretty close in. Tomorrow night they will all be on the west side of the planet. The waxing Gibbous Moon shows most of the Earth facing side now. The sunrise line a day ago brought the crater Copernicus into light on the east or left side of the Moon. Otherwise the east side of the Moon is flatter than the west side being dominated by two flat lunar seas, actually lava plains called the Sea of Clouds and Ocean of Storms. The Moon has never seen clouds or storms.

The event times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

Jupiter, Saturn and the Moon as they would appear to the naked eye at 9:33 pm tonight August, 28, 2020. Created using Stellarium which unfortunately shows the Moon dimmer than the planets. In reality is that the Moon very much brighter, almost overpowering the planets.

Jupiter and its 4 Galilean moons as the would appear in a telescope tonight August 28, 2020. Created using Cartes du Ciel (Sky Chart).

The gibbous Moon tonight as it might appear in a low power telescope. Created using Stellarium.

 

08/04/2020 – Ephemeris – Viewing Jupiter and its moons with binoculars or small telescope

This is Ephemeris for Tuesday, August 4th. Today the Sun will be up for 14 hours and 30 minutes, setting at 9:03, and it will rise tomorrow at 6:34. The Moon, 1 day past full, will rise at 10:06 this evening.

The planet Jupiter is a fine object to view with just about any optical aid be it a pair of binoculars, spotting scope or telescope. In binoculars, if held steady or mounted on a tripod Jupiter itself will no longer look star-like, but a tiny disk. Several of Jupiter’s moons can also be seen. With a telescope four of them can be seen, the same four Galileo discovered 410 years ago. At 10 pm they will be in the same order of distance from the planet that they actually are. The two nearest will be on the west side of the planet Io the closest, the Europa the next moon out. On the east side there is the third farthest Ganymede, and farthest out is Callisto. Their orbits are nearly edge on to us, so they shuttle from one side to the other of the planet.

The event times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

Jupiter and its Galilean moons for tonight and tomorrow night August 4 & 5, 2020. Those moons really move from night to night. This is shown north at the top, east to the left. Based on telescope design the image presented could be inverted, mirror image or both. Created using Cartes du Ciel (Sky Charts).

Due to the lack of time (59 seconds) I could only cover the moons. I’ll address Jupiter’s cloud features at another time. Can’t wait? Here’s a link: https://bobmoler.wordpress.com/2018/05/22/05-22-2018-ephemeris-seeing-detail-on-the-face-of-jupiter-with-a-small-telescope/

01/21/2019 – Ephemeris – Venus and Jupiter will pass each other tomorrow morning

Ephemeris for Martin Luther King Jr. Day, Monday, January 21st. Today the Sun will be up for 9 hours and 23 minutes, setting at 5:35, and it will rise tomorrow at 8:11. The Moon, at full today, will rise at 6:23 this evening.

I hope you’ve been noticing the bright planets Venus and Jupiter in the morning this month on the few mornings that have been clear. Jupiter and Venus have been drawing together. And tomorrow morning they will pass each other. The event is called a conjunction. To astronomers it’s a cool looking event, where the planets happen to be along the same line of sight. They are nowhere near each other in actuality. Venus is 76 million miles (120 million km) away, while Jupiter is 555 million miles (894 million km) away. It doesn’t affect anything on the Earth. It’s just cool looking. After this, Jupiter will move farther and farther from the Sun, while Venus will appear to fall back towards the Sun, even though they both are traveling eastward against the stars.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

Three day animation of Venus and Jupiter on the 21st, 22nd, and 23rd of January 2019. Created using Stellarium and GIMP.

05/29/2018 – Ephemeris – Jupiter, big and massive

Ephemeris for Tuesday, May 29th. Today the Sun will be up for 15 hours and 16 minutes, setting at 9:18, and it will rise tomorrow at 6:01. The Moon, at full today, will rise at 9:21 this evening. | Jupiter is not only the largest planet, but the largest appearing planet pretty much all the time. Venus can look larger when it is a thin crescent about to or having just passed between the Earth and the Sun. Mars, because of its small actual size, that of half the Earth varies greatly in distance, and at its closest appears about half the size of Jupiter in telescopes. Jupiter’s great mass is the key to reasonable travel times of spacecraft to Saturn and beyond. A spacecraft sent to catch up to Jupiter will be accelerated with respect to the Sun into a faster trajectory to arrive at their destination sooner. New Horizon’s trip to Pluto would have taken 13 years, that’s 3 years longer without Jupiter’s gravity assist.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

New Horizons trajectory as of last April showing the effect og Jupiter’s gravitational assist. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

05/28/2018 – Ephemeris – NASA’s Juno spacecraft takes deep dives at Jupiter

Ephemeris for Memorial Day, Monday, May 28th. Today the Sun will be up for 15 hours and 15 minutes, setting at 9:17, and it will rise tomorrow at 6:02. The Moon, 1 day before full, will set at 6:24 tomorrow morning.

NASA’s Juno spacecraft has made 11 close passes of Jupiter since being inserted into Jovian orbit in July 2016. It has a highly elliptical orbit. It comes in over the north pole, passes only 2,000 miles over the cloud tops at the equator and heads out over the south pole, avoiding the most intense parts of Jupiter’s radiation belts. The high latitude and polar clouds appear more chaotic than expected. We can’t see these very well from the Earth. The magnetic field is much stronger and lumpier than thought before. A very much improved and complex picture of our largest planet is emerging, as we expected. The mission isn’t over and years of analysis are ahead to begin to more fully understand the solar system’s greatest planet.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addenda

Chaotic storms at Jovian high latitudes. Credit NASA/JUNO

Jupiter’s North Pole in the infrared. 8 cyclones surrounding a 9th at the pole. Credit: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM

Jupiter’s South Pole in the infrared. 5 cyclones surrounding a 6th at the pole. Credit: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM

Alan Bean

Astronaut Alan Bean, 4th person to walk on the Moon with Apollo 12 passed away this weekend.  He also commanded the second Skylab mission and retired to become an artist, a painter of his adventures on the Moon and in space.  Of the twelve men who walked on the Moon, only four survive.

05/24/2018 – Ephemeris – Jupiter is really BIG

Ephemeris for Thursday, May 24th. Today the Sun will be up for 15 hours and 8 minutes, setting at 9:14, and it will rise tomorrow at 6:05. The Moon, 3 days past first quarter, will set at 4:24 tomorrow morning.

Jupiter is a big planet. How big is it? One could fit thirteen hundred Earths inside it. Even so Jupiter has the mass of only 318 Earths, so Jupiter is made of lighter stuff than the Earth, including a lot of hydrogen and helium. NASA’s Juno spacecraft is currently orbiting Jupiter, working that out. Still, Jupiter is massive. The late science and science fiction writer Isaac Asimov wrote that the solar system consists of the Sun, Jupiter and debris. Jupiter contains more than twice the mass of all the other planets and asteroids combined. Jupiter is also surrounded by a huge set of radiation belts, lethal to all but the most radiation hardened spacecraft. And that goes for would be astronauts too.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

Planet size comparison. Note that even though Saturn looks almost as large as Jupiter it is less than 30% of Jupiter’s mass. From connormorency.wordpress.com