Archive
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.
Addendum
Ephemeris: 12/16/2024 – The Europa Clipper mission
This is Bob Moler with Ephemeris for Monday, December 16th. Today the Sun will be up for 8 hours and 48 minutes, setting at 5:03, and it will rise tomorrow at 8:14. The Moon, 1 day past full, will rise at 6:09 this evening.
Just two months ago the satellite to closely study Jupiter’s second Galileo moon Europa was launched from Cape Canaveral on a Falcon Heavy rocket. The satellite’s name is Europa Clipper. It was originally scheduled to be launched by the SLS rocket but this rocket which is used for the Artemis program was not going to be ready for the mission so they dropped back to the somewhat less powerful SpaceX Falcon Heavy rocket. Europa Clipper will take 5 1/2 years to travel out to Jupiter with first a gravitational boost from a flyby of Mars and then another one a flyby of Earth to gain enough speed to make it to Jupiter. There it would orbit Jupiter in such a way as to fly by Europa multiple times. Jupiter’s radiation is harsh at Europa’s distance, so the satellite has to get in and get out quickly.
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: 12/13/2024 – The Geminid meteor shower peaks tonight
This is Bob Moler with Ephemeris for Friday, December 13th. Today the Sun will be up for 8 hours and 50 minutes, setting at 5:02, and it will rise tomorrow at 8:12. The Moon, 2 days before full, will set at 7:45 tomorrow morning.
Tonight is the peak of the Geminid meteor shower. Unfortunately this year we’re two days before a full moon so it will cut down their numbers, so only the brightest Geminids will be visible. The radiant for the meteor shower is a point near the star Castor at the head of constellation Gemini, the twins, which is why they’re called the Geminids. This is the most active annual shower of the year right now. The source of the Geminids is the asteroid Phaethon which is probably the core of a dead comet. It is the closest asteroid to the sun at its perihelion in its markedly elliptical orbit like a comet. One of the Stereo Sun observation satellites saw Phaethon shedding material as it moved around at its closest approach to the Sun.
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: 12/12/2024 – Jupiter’s moon Europa
This is Bob Moler with Ephemeris for Thursday, December 12th. Today the Sun will be up for 8 hours and 51 minutes, setting at 5:02, and it will rise tomorrow at 8:12. The Moon, 3 days before full, will set at 6:24 tomorrow morning.
Jupiter’s four bright Galilean moons are nearly planet size. In fact Ganymede, the third one out, is larger than Mercury. But the most interesting moon to NASA and to scientists looking for life in the solar system, is the second moon out, Europa. When the Voyager spacecraft flew past Jupiter in the late 1970s they photographed a rather smooth surface on it with a lot of cracks and grooves, but very few craters. This meant Europa surface is quite young and has been evolving over time kind of like the Earth’s surface. The reason is that it appears Europa has a vast ocean under a thick crust of ice. Europa is heated by both radioactivity in its core and tidal forces caused by Jupiter and the other moon’s gravitational pull on 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.
Addendum
On Earth, wherever there’s water there’s life. Can the same be said of Europa?
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.
Addendum
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.
Addendum
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: 12/09/2024 – Today’s sunset is the earliest of the year
This is Ephemeris for Monday, December 9th. Today the Sun will be up for 8 hours and 53 minutes, setting at 5:02, and it will rise tomorrow at 8:09. The Moon, 1 day past first quarter, will set at 2:20 tomorrow morning.
Today is the date of the earliest sunset, in the middle of a 13-day stretch where the Sun sets within the same minute. We are still 12 days from the winter solstice, the day of the shortest daylight hours, on the 21st. The reason is twofold. The Sun is approaching its farthest position south of the equator, where the longitude lines are closer together, so it takes less time to cross them. 15 degrees in longitude equals one hour in Earth’s rotation. Add to that we are less than a month from Earth’s perihelion in its orbit of the Sun, that is at its closest, and is moving faster than average. The combined effects delay sunrise and sunset, from what they’d be if the Sun stayed on the equator and the Earth’s orbit was circular. We will have our latest sunrise on January 2nd.
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: 12/06/2024 – Historical search for the Star of Bethlehem tonight
This is Ephemeris for Friday, December 6th. Today the Sun will be up for 8 hours and 56 minutes, setting at 5:02, and it will rise tomorrow at 8:06. The Moon, 2 days before first quarter, will set at 10:31 this evening.
Tonight at 8 p.m. I will be giving a talk investigating what the Star of Bethlehem may have been. This will be at Northwestern Michigan College’s Rogers Observatory located south of Traverse City on Birmley Road. The talk is a scientific treatment of the matter, rather than a religious one. We’ll look at the usual suspects for what the star may have been. And we’ll see what the Gospel writers may have gotten right and possibly wrong. We’ll look at historical writings and recorded Chinese observations of the heavens around that time. I will augment this with computer simulations of what might be important celestial events visible around that time. There is no admission charge. There will be viewing of the skies afterward if it’s clear.
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: 12/05/2024 – 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
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