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Ephemeris: 04/29/2025 – Using the Sun as a telescope
This is Ephemeris for Tuesday, April 29th. Today the Sun will be up for 14 hours and 10 minutes, setting at 8:45, and it will rise tomorrow at 6:33. The Moon, 2 days past new, will set at 11:56 this evening.
One idea of a telescope I find very fantastic. This is a telescope that uses the Sun and its mass curving spacetime to alter the path of light from a distant object to act like a lens in a telescope. This is called gravitational lensing. The length of this telescope would have to be about 542 times the earth’s distance from the Sun, 542 astronomical units. In the 48 years since Voyager 1 was launched it has achieved only about 1/3 of that distance. What would be the use of this telescope would be to image exoplanets. So far exoplanets, if they are visible at all, don’t even cover a single pixel in even our largest telescopes. The problems are huge, starting with gravitational lenses don’t bend light the same way as optical ones do.
The astronomical event times given in this blog are for the Traverse City/Interlochen area of Michigan (Lat 44.7° N, Long 85.7° W; EDT, UT – 4 hours) unless stated otherwise. Times will be different for other locations.
Addendum
Here are some sources of additional information on this topic:
https://www.universetoday.com/articles/how-can-the-sun-become-a-telescope
https://www.livescience.com/space/the-sun/could-we-turn-the-sun-into-a-gigantic-telescope
https://nasaspacenews.com/2025/04/see-alien-planets-in-4k-the-suns-gravitational-lens-explained/
https://news.stanford.edu/stories/2022/05/gravity-telescope-image-exoplanets
https://www.space.com/sun-gravity-could-help-observe-exoplanets-in-detail
Ephemeris: 02/24/2025 – Mars stopped in its tracks!
This is Ephemeris for Monday, February 24th. Today the Sun will be up for 10 hours and 55 minutes, setting at 6:24, and it will rise tomorrow at 7:26. The Moon, 3 days before new, will rise at 6:30 tomorrow morning.
Today the planet Mars is said to be stationary. No, planets do not stop in their orbits of the Sun. It is because we are viewing them from the moving planet Earth. For the last few months Mars has been moving to the west, which is not its normal motion, so we call it retrograde motion. It does that because the Earth, moving faster on an inner orbit, is passing Mars moving slower on an outer orbit. This was a problem for the ancients of the western world because they thought all the moving objects, all seven of them, moved around a stationary Earth. Of those seven, two of them never went backwards, or westward against the stars. They were: the Moon which does orbit the Earth and the Sun which the Earth orbits.
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
* For non astronomers: Inferior doesn’t refer to quality, but that the planet’s orbit is inside the Earth’s orbit. Superior planets orbit farther out from the Sun than the Earth.
Ephemeris: 01/14/2025 – Mars reaches opposition tomorrow – What that means
This is Ephemeris for Tuesday, January 14th. Today the Sun will be up for 9 hours and 10 minutes, setting at 5:27, and it will rise tomorrow at 8:16. The Moon, 1 day past full, will rise at 6:14 this evening. | Tomorrow the planet Mars will be in opposition to the Sun. That means it will rise at sunset and set at sunrise. This is the time we are closest to Mars or near closest to Mars of its current pass. Mars comes in opposition from the Sun about every 26 months on average. Currently, Mars is farther from the Sun than average. It has a large swing in distances from the Sun and so at this time moves slower than average. The time between oppositions is only 25 months currently. The various space agencies know that opposition time is the best time to launch spacecraft to Mars. However, they launch several months ahead of opposition for the spacecraft to arrive several months after opposition for the least amount of energy needed for the journey.
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: 01/09/2025 – Venus is at its greatest separation from the Sun today
This is Ephemeris for Thursday, January 9th. Today the Sun will be up for 9 hours and 2 minutes, setting at 5:21, and it will rise tomorrow at 8:18. The Moon, 3 days past first quarter, will set at 5:25 tomorrow morning.
Tonight, Venus will be at its greatest separation from the Sun in the sky at a little bit more than a 47° angle. Venus, being inside the Earth’s orbit, can ever stray far from the Sun. So today it is at its greatest eastern elongation from the Sun. For the rest of winter it will be moving closer to the Sun from our perspective. Crossing between the Earth and the Sun on March 22nd. During this period of time Venus will be a great object for the telescope, as it moves closer to the Earth and gets larger in telescopes and its phase, moving from being like a quarter moon to a very thin crescent near the end of winter. At inferior conjunction with the Sun, Venus will be only 26 million miles away from us, but quite invisible in the Sun’s glare.
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 Mayan civilization of Central America had several calendars. One of them was based on the planet Venus. They discovered that Venus repeated its positions in the sky with respect with the seasonal calendar over a period of eight years, which they called a Venus Sequence. They paid close attention to Venus and discovered it appeared to go around the Sun in the sky in 584 days, which they called a Venus Cycle. We call it Venus’ synodic period, which is the number of days between inferior conjunction, when Venus passes between the Earth and the Sun, then moves through the morning sky, and disappears behind the Sun at superior conjunction, then appears in the evening sky and back to inferior conjunction again. The gray area in the diagram is where Venus is not visible because it’s too close to the sun. However, at our latitude the number of days that Venus is invisible varies with the season. The Mayans, being in the tropics, didn’t have as much variation as we do. The Mayans discovered that Venus completed 5 cycles in almost exactly 8 years.
Today, Venus is at its greatest eastern elongation. On March 22nd Venus will pass inferior conjunction. That is 72 days from today. So it spends most of its time, 7 months, moving from around behind the Sun to the greatest elongation and only a short time, about 2 1/2 months moving from there to inferior conjunction. These 2 1/2 months are the best time to view Venus with a telescope, since Venus will grow in size and become an ever thinning crescent.
Check out my Wednesday posts showing the ever-growing and thinning Venus crescent until March 22nd. Or better yet, see it for yourself with a small telescope.
Ephemeris: 01/02/2025 – Today we have the latest sunrise
This is Bob Moler with Ephemeris for Thursday, January 2nd. The Sun will rise at 8:20. It’ll be up for 8 hours and 54 minutes, setting at 5:14. The Moon, 3 days past new, will set at 8:20 this evening. | As an amateur astronomer I am fascinated by time, the so-called 4th dimension. For example, being at the right place at the right time such as to view a total solar eclipse. The universe isn’t going to wait for you if you’re off in the three dimensions of location or of the time. But today is a different story. Today is the day of the latest sunrise, which is at 8:20 AM. From today to June 15th, the day of the earliest sunrise, is on average about 165 days. That’s about 5 ½ months. We had our earliest sunset back on December 9th. That was 24 days ago so it’s got a head start from there to the latest sunset that it will need because the latest sunset will be on June 26th. So the sunrise times will decrease faster than the sunset times will increase into the June summer solstice period.
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: 12/09/2024 – 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: 11/18/2024 – How to get two spacecraft to come together gently in space
This is Bob Moler with Ephemeris for Monday, November 18th. Today the Sun will be up for 9 hours and 26 minutes, setting at 5:11, and it will rise tomorrow at 7:45. The Moon, 3 days past full, will rise at 7:22 this evening.
Orbital mechanics is a science of how orbits work around the Earth, Sun, or any other body. Back in the mid 1960s when NASA was starting it’s work to get to the Moon with the Gemini program they had quite a time getting rendezvous and docking right. Buzz Aldrin, the second man to step foot on the Moon, who is still around by the way, figured it all out – before he became an astronaut. It’s counter-intuitive. To speed up you slow down to drop into a lower orbit which is faster. To slow down, speed up and climb into a higher orbit which slows you down. There’s more to it than that, but basically objects in orbit just don’t seem to behave the way you think they ought to. And that’s how things work in space.
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
In this diagram time is represented on the horizontal axis from right to left, the altitude of the spacecraft and its target is on the vertical axis. The chaser vehicle is launched as the launch site crosses the plane of the orbit of the target. Changing the plane of an orbit is very expensive, energywise, so it’s best to launch in the same orbital plane. It enters an elliptical orbit, most initial orbits are pretty elliptical and so there’s a low point, or perigee, where the chaser enters orbit, and a high point which is the apogee. This is below the target orbit so that the chasing vehicle can catch up to the target. Lower orbits are faster than higher orbits, this is the phasing part. When the chaser gets pretty close it raises its orbit so that the starting point apogee is the new perigee and the new apogee is the altitude of the orbit of the target. The orbit stays elliptical for a little while so that the chasing spacecraft can slowly catch up to the target. In the final approach the orbits just about match so that the chaser very slowly catches up to the target.
I’ve seen similar diagrams on NASA broadcasts of Crew Dragon launches.
Ephemeris: 11/15/2024 – What causes the tides?
This is Ephemeris for Friday, November 15th. Today the Sun will be up for 9 hours and 33 minutes, setting at 5:14, and it will rise tomorrow at 7:41. The Moon, at full today, will rise at 4:48 this evening.
Today, at full moon, is one of the two highest tides of the month, the lunar month that is. The other highest tide comes at new moon. Both the Moon and the Sun cause tides because of their gravitational pull on the Earth. At new and full moon’s their gravitational pull gangs up on us. Since Earth is not a point body the gravitational pull of an object on the near side of the Earth pulls harder than it does on the opposite side of the Earth. Gravitational force diminishes with the square of the distance so it is the difference in the gravitational pull from one side to the other of the Earth that causes the tides to rise up on the side nearest and farthest from the gravitational pull of the moon and/or Sun. Since the Earth has a worldwide ocean, the water is free to slosh around and cause the tides.
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: 11/12/2024 – SpaceX uses Cargo Dragon to change orbit of the ISS
This is Bob Moler with Ephemeris for Tuesday, November 12th. Today the Sun will be up for 9 hours and 40 minutes, setting at 5:17, and it will rise tomorrow at 7:37. The Moon, halfway from first quarter to full, will set at 4:39 tomorrow morning.
After the last SpaceX cargo mission arrived at the International Space Station, they used the thrusters on the SpaceX capsule to raise the orbital space station a little bit as a test. SpaceX capsules dock at the forward end of the space station according to direction of travel so in order to boost the station’s orbit they had to flip the station around so that the docking port was at the rear before they could apply the needed thrust. When thrust is applied to an object in orbit the effect of the change occurs mostly at the opposite side of the orbit. In order to permanently raise or lower an object’s circular orbit one must make 2 adjustments 180° away from each other. This is the essence of the Hohmann Transfer Orbit, proposed by German scientist Walter Hohmann in 1925.
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: 11/07/2024 – The Moon wobbles from Earth’s point of view
This is Ephemeris for Thursday, November 7th. Today the Sun will be up for 9 hours and 53 minutes, setting at 5:22, and it will rise tomorrow at 7:31. The Moon, 2 days before first quarter, will set at 10:08 this evening.
The nearly seven day old Moon appears very low in the southwestern sky tonight. It appears as a fat crescent. The small sea called Mare Crisium or Sea of Crises, near the west edge of the Moon is a good indicator of what we call libration, that is the Moon’s slow wobbling back and forth over the month as it orbits the Earth. One can judge the amount of libration by the distance of that small round sea from the edge of the Moon. This happens because the Moon’s rotation is steady while its orbital velocity around the Earth is not, because its orbit is slightly elliptical. So sometimes the rotation gets ahead of its revolution about the Earth, and sometimes it’s behind. Right now that libration is pushing that small sea towards the edge of the Moon.
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
Bob Moler's Ephemeris Blog 