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Ephemeris: 12/17/2024 – A closeup look at Ganymede
This is Bob Moler with Ephemeris for Tuesday, December 17th. Today the Sun will be up for 8 hours and 48 minutes, setting at 5:03, and it will rise tomorrow at 8:15. The Moon, 2 days past full, will rise at 7:23 this evening. | Ganymede is the largest satellite in the solar system orbiting the largest planet in the solar system, Jupiter. It is 1 1/2 times the diameter of our Moon, and slightly larger than the planet Mercury. It is an icy moon, being about half made-up of water ice and silica. Ganymede appears to have a below surface ocean of water like Europa. And its surface appears to be quite smooth, not as smooth as Europa’s but parts of it are literally devoid of craters for the most part, and many of the craters it does appear to have inner craters in the center which looks quite weird. The Juno spacecraft, still orbiting Jupiter, took some very close images of Ganymede back in 2021 using its relatively simple camera. These were some of the best images of it.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT – 5 hours). Times will be different for other locations.
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Ephemeris: 12/11/2024 – Where are the naked-eye planets this week?
This is Ephemeris for Wednesday, December 11th. Today the Sun will be up for 8 hours and 51 minutes, setting at 5:02, and it will rise tomorrow at 8:11. The Moon, 3 days past first quarter, will set at 5:00 tomorrow morning.
Let’s take our weekly look at the whereabouts of the naked-eye planets. Venus can be spotted in the south-southwestern sky by 5:30 PM, about 30 minutes after sunset. It will set at 8:25 PM. Saturn will be in the south at 6 PM, way above the bright star Fomalhaut. Jupiter is low in the east-northeast, about the same time as when Venus is first spotted. It will be a good object for the small telescope about an hour later. Mars, rises tonight at 8:17, Mars is still considered a morning planet since it is still up at sunrise. By 6:00 AM tomorrow Jupiter will be low in the west-northwest, to the right of the setting Orion, while reddish Mars will be high in the west-southwest.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT – 5 hours). Times will be different for other locations.
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Ephemeris: 12/10/2024 – Jupiter’s four bright moons
This is Ephemeris for Tuesday, December 10th. Today the Sun will be up for 8 hours and 52 minutes, setting at 5:02, and it will rise tomorrow at 8:10. The Moon, 2 days past first quarter, will set at 3:39 tomorrow morning.
The bright star like object in the east in the evenings is the planet Jupiter. If one were to look at Jupiter through binoculars it would appear somewhat larger than a star would look. It has several dimmer stars from one side to the other of it, and if one looked the next night those little stars would have moved. Those are not stars at all, but the four largest moons of Jupiter. This would be easily apparent in the telescope. These are the four Galilean moons. They were observed by Galileo in either late 1609 or early 1610. Another astronomer, Simon Marius discovered these moons at about the same time, but Galileo was first to publish. So he gets the honor. However, Simon Marius is the one who gave them the names we know them by today. Their names, in order of their distance from Jupiter, are: Io, Europa, Ganymede, and Callisto. Each is a fascinating world in its own right.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT – 5 hours). Times will be different for other locations.
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The periods of these satellites is interesting. Io orbits Jupiter in 1.8 days. Europa orbits in 3.6 days twice as long as Io. Ganymede orbits Jupiter in 7.2 days which is twice as long as Europa. Callisto takes 16.7 days to orbit Jupiter, and that is longer than twice Ganymede’s orbital period, and so is not in resonance with Ganymede. So the first three are in a 2:1orbital resonance with each other.
Ephemeris: 12/05/2024 – More about Jupiter: it’s very gassy
This is Bob Moler with Ephemeris for Thursday, December 5th. Today the Sun will be up for 8 hours and 57 minutes, setting at 5:02, and it will rise tomorrow at 8:05. The Moon, 3 days before first quarter, will set at 9:14 this evening.
The planet Jupiter rules over the night sky with the Moon after Venus sets. Jupiter, 11 times the diameter of the Earth, has the volume of 1300 earths, however it is only 318 times the mass of the Earth. It is made-up mostly of hydrogen and helium, so it is called a gas giant planet, rather than a terrestrial or rocky planet like the Earth. Jupiter is the best viewable of the planets in a small telescope. It has 2 dark bands across it called belts of darker appearing clouds. The famed Great Red Spot is an anticyclone embedded in the southern of those belts. The spot is not as red anymore. I remember it being brick-red back in the late 1950s and early 60s. Jupiter spins very rapidly, its day lasts only 10 hours.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT – 5 hours). Times will be different for other locations.
Addendum

Ephemeris: 12/04/2024 – Checking where the naked-eye planets are now
This is Ephemeris for Wednesday, December 4th. Today the Sun will be up for 8 hours and 58 minutes, setting at 5:02, and it will rise tomorrow at 8:04. The Moon, 3 days past new, will set at 7:59 this evening.
Let’s take our weekly look at the whereabouts of the naked-eye planets. Venus can be spotted low in the south-southwestern sky by 5:30 PM, about 30 minutes after sunset. It appears above the Moon tonight, and will set at 8:09 PM. Saturn will be in the south-southeast at 6 PM. Jupiter will rise at 5:09 PM in the east-northeast, and be a good object for the small telescope about an hour later. Mars, rises tonight at 8:47, Both Mars and Jupiter are considered morning planets, since they are still up at sunrise, though Jupiter will be an evening planet after Saturday. By 6:00 AM tomorrow Jupiter will be in the west, above and right of Orion, while reddish Mars will be high in the southwest. Jupiter and Saturn are great planets to view with a small telescope.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT – 5 hours). Times will be different for other locations.
Addendum







Ephemeris: 12/03/2024 – Jupiter begins to dominate the evening sky
This is Ephemeris for Tuesday, December 3rd. Today the Sun will be up for 9 hours even, setting at 5:02, and it will rise tomorrow at 8:03. The Moon, 2 days past new, will set at 6:48 this evening.
The bright star that’s in the east early in the evenings isn’t a star at all, but the planet Jupiter. This giant planet is moving to be in opposition to the Sun this Saturday, which means that the Earth is directly between Jupiter and the Sun, so it’s the time that it’s closest to us. And so it’s at its largest appearing and brightest. Jupiter is the largest of the planets being about 11 times the Earth’s diameter, its volume would be 11 cubed or about 1,300 times the Earth’s volume. It is the second-brightest planet after Venus. It is also the largest appearing planet in telescopes except for a couple of months around the time when Venus is closest to the Earth. Binoculars will show that Jupiter is not quite star-like, and some of its large satellites can be also seen.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT – 5 hours). Times will be different for other locations.
Addendum

Ephemeris: 11/27/2024 – Checking up on the naked-eye planets this week
This is Ephemeris for Wednesday, November 27th. Today the Sun will be up for 9 hours and 9 minutes, setting at 5:05, and it will rise tomorrow at 7:57. The Moon, 4 days before new, will rise at 5:23 tomorrow morning.
Let’s take our weekly look at the whereabouts of the naked-eye planets. Venus can be spotted low in the south-southwestern sky by 5:30 PM, about 25 minutes after sunset. It will set at 7:52. Saturn will be in the south-southeast at 6 PM. Jupiter will rise at 5:45 PM in the east northeast, and be a good object for the small telescope about an hour later. Mars, rises tonight near 9:16, Both Mars and Jupiter are considered morning planets, since they are still up at sunrise. By 6 AM tomorrow Jupiter will be in the west, above and right of Orion, while reddish Mars will be high in the southwest. Jupiter and Saturn are good planets to view with a small telescope, Mars will appear only a quarter the diameter of Jupiter.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT – 5 hours). Times will be different for other locations.
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Ephemeris: 11/20/2024 – Our weekly look at the naked-eye planets
This is Ephemeris for Wednesday, November 20th. Today the Sun will be up for 9 hours and 22 minutes, setting at 5:09, and it will rise tomorrow at 7:48. The Moon, 2 days before last quarter, will rise at 9:45 this evening.
Let’s take our weekly look at the whereabouts of the naked-eye planets. Venus can be spotted low in the southwestern sky by 5:30 PM, about 20 minutes after sunset. It will set at 7:41. Saturn will be in the south-southeast at 6 PM. Jupiter will rise at 6:11 PM in the east northeast, and be a good object for the small telescope about an hour later. Mars, rises tonight near 9:36, just ahead of the Moon and will be leading it through the night skies tonight. By 6:00 AM tomorrow Jupiter will be in the west, above and right of Orion, while reddish Mars will be high in the southwest to the right of the waning gibbous Moon. Jupiter and Saturn are good planets to view with a small telescope, Mars will appear only a quarter the diameter of Jupiter.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT – 5 hours). Times will be different for other locations.
Addendum







Ephemeris: 11/06/2024 – Where are the naked eye planets this week?
This is Ephemeris for Wednesday, November 6th. Today the Sun will be up for 9 hours and 55 minutes, setting at 5:24, and it will rise tomorrow at 7:29. The Moon, 3 days before first quarter, will set at 8:56 this evening.
Let’s take our weekly look at the whereabouts of the naked-eye planets. Venus can be spotted low in the southwestern sky by 6 PM, about half an hour after sunset. It will set at 7:22. Saturn will be in the southeast at 7 PM. Jupiter will rise at 7:17 PM in the east northeast, and be a good object for the small telescope about an hour later. By 6:00 AM tomorrow Jupiter will be high in the west southwest, among the winter stars, while reddish Mars, which rises tonight near 10:16, will be high in the south. Jupiter and Saturn are good planets to view with a small telescope, while Venus and Mars will appear very small and featureless. These last two will improve next year when they move closer to us.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT – 5 hours). Times will be different for other locations.
Addendum







Ephemeris: 10/30/2024 – Our weekly look at the whereabouts of the naked-eye planets
This is Ephemeris for Wednesday, October 30th. Today the Sun will be up for 10 hours and 14 minutes, setting at 6:33, and it will rise tomorrow at 8:20. The Moon, 2 days before new, will rise at 7:28 tomorrow morning.
Let’s take our weekly look at the whereabouts of the naked-eye planets. Venus can be spotted low in the southwestern sky by 7 PM, about half an hour after sunset. It will set at 8:18. Comet Tsuchinshan-ATLAS is definitely a binocular object and will be a third of the way up to the zenith in the southwest around 8 PM. It will set at 11:17 PM. Saturn will be in the southeast at 8 PM. Jupiter will rise at 8:42 PM in the east northeast, and be a good object for the small telescope about an hour later. By 7:00 AM tomorrow Jupiter will be high in the west southwest, among the winter stars, while Mars, which rises tonight near 11:30, will be high in the south.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hours). Times will be different for other locations.
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