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Ephemeris: 11/14/2023 – Lucy sees an asteroid with a double moon
This is Bob Moler with Ephemeris for Tuesday, November 14th. Today the Sun will be up for 9 hours and 37 minutes, setting at 5:15, and it will rise tomorrow at 7:39. The Moon, 1 day past new, will set at 5:48 this evening.
Two years ago a spacecraft called Lucy was sent out towards the Trojan Asteroids of Jupiter. On the way there it was going to pass another small asteroid, but they found another one that Lucy would come close to, the mission planners tweaked its orbit earlier this year. So Lucy can get close to the small asteroid called Dinkinesh. When Lucy got close to Dinkinesh earlier this month, it took photos, and they found that it had a satellite, and they took other photos from a different angle, and they found out that the satellite actually was two satellites in contact, a contact binary, two bodies stuck together. So that was quite a surprise. Neither body looked smooshed, so their collision appears to have been very gentle.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT –5 hours). They may be different for your location.
Addendum
Dinkinesh is the Ethiopian name for the fossil, since it was found in Ethiopia. The name for the fossil given by the discoverers was Lucy, mainly because The Beatles song Lucy in the sky with diamonds was a big hit back then, and it was constantly played in the camp.
The next main belt asteroid that Lucy is going to pass on its way out to Jupiter’s Trojan asteroids is named Donaldjohansson in honor of the discoverer of the Lucy fossil. Jupiter’s Trojan asteroids are two groups of asteroids in the same orbit as Jupiter. One set is 60 degrees ahead of Jupiter in its orbit and the second set is 60 degrees behind Jupiter in its orbit. They’re there because they are at special gravitational points called Lagrangian points. The point ahead of Jupiter is the L4 point and the one trailing is L5. You may have heard me talk about L1 and L2 points having to do with the Earth and Sun system. These are two other Lagrangian points in line with the Sun-Earth axis, that are useful to orbit spacecraft around. There’s another one, but we don’t think there’s anything out there because that’s on the other side of the Sun from us, and none of the other planets have a body opposite to the Sun from them either, so the L3 point is not a viable point.
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.
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