12/17/2017 – Ephemeris – What is a Lagrange Point?
Ephemeris for Monday, December 17th. The Sun will rise at 8:14. It’ll be up for 8 hours and 48 minutes, setting at 5:03. The Moon, 2 days past first quarter, will set at 3:15 tomorrow morning. |
Newton’s law of gravitation allows for some gravitational equilibrium points around two bodies that orbit each other. Discovered in th 18th century by Leonhard Euler and Joseph-Louis Lagrange these are known as Lagrange or L points. There are five. L1 is between the two bodies. The L1 point between the Earth and Sun is a million miles sun-ward of the Earth, where we station solar observation satellites. L2 is a million miles in the other direction, where there are astronomy satellites looking anywhere but the Sun. The James Webb telescope will join them there. L3 is point on the other side of the Sun, for which no use has yet been found. L4 and L5 are 60 degrees ahead of and behind the Earth’s position in its orbit. These are quite stable. Jupiter has thousands of asteroids in its L4 and L5 locations called Trojan asteroids.
The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
The 5 Lagrange points about two bodies M1 and M2 orbiting each other. Credit Georgia State University.
12/15/2018 – Ephemeris Extra – Finally the skies cleared and I got a photograph of Comet Wirtanen
Comet 46P/Wirtanen and the Pleiades. 9:24 p.m. EST, December 14, 2018. Canon EOS Rebel T5, f/5.5, 30 sec., ISO-3200, fl 55mm, tracking. Click on the image to enlarge. Credit Bob Moler.
Finally, the skies cleared. The last time we had clear skies was early in the evening on the 8th. Our family went to the Ballet that evening at Interlochen Center for the Arts, and by the time I got back and dressed to go outside and observe the comet, it had clouded up. The Ballet was wonderful, by the way.
Anyway, Comet 46P/Wirtanen as a few hours ago was greatly hampered by the nearly first quarter Moon. And it’s going to get worse as the moon’s phase gets fuller. I thought I could see it in with the naked eye. It was visible in binoculars. As you can see it did photograph well. I processed the image with GIMP to increase contrast, and reduce the background moonlight. There is no discernible tail visually or in this photograph. Longer exposures in a dark sky do show a faint ion tail. Remember this is a short period comet, and has been around the Horn (perihelion) innumerable times. It orbits the Sun from just inside Jupiter’s orbit to just outside Earth’s orbit every 5.4 years.
Happy comet hunting!
12/14/2018 – Ephemeris – Bright Comet Wirtanen will be easy to find this weekend
Ephemeris for Friday, December 14th. The Sun will rise at 8:12. It’ll be up for 8 hours and 50 minutes, setting at 5:02. The Moon, 1 day before first quarter, will set at 12:06 tomorrow morning.
This weekend is the best time to spot Comet Wirtanen. Not only is near its brightest, but it will be passing just to the left of the beautiful star cluster the Pleiades from below. Comet Wirtanen will appear as a fuzzy spot, possibly to the naked eye, but is best seen in binoculars. The near first quarter Moon will be a bother, and make the comet harder to spot. On the 12th the comet passed its closest to the Sun, called perihelion, about 4.6 million miles outside the Earth’s orbit. On the 16th, Sunday, it will pass closest to the Earth at 7.2 million miles, as the 10th closest comet passage in modern times. Wirtanen is a member of the Jupiter family of comets captured by and orbit maintained by the planet Jupiter.
The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Comet 46P/Wirtanen positions for the next week. Positions are marked with month-date and magnitude. The latest magnitude prediction for December 15th is 3.3, 5.5 magnitudes brighter than shown here. Star field position is for 9 p.m. on the 12th. Click on the image to enlarge. Created using Cartes du Ciel (Sky Charts).
12/13/2018 – Ephemeris – The Geminid meteors will reach their peak numbers overnight
Ephemeris for Thursday, December 13th. The Sun will rise at 8:11. It’ll be up for 8 hours and 50 minutes, setting at 5:02. The Moon, 2 days before first quarter, will set at 11:05 this evening.
Tonight through the morning hours we will have the chance to see the peak of the Geminid meteor shower. The meteors will be most numerous tomorrow morning. This shower is currently besting the Perseid meteor shower of August with a predicted 120 meteors per hour at the peak. The problems for us in viewing this fabulous shower are the cold temperatures and usually cloudy skies. However the Moon will be a problem until it sets after 11 p.m. The source of the Geminids was discovered in 1983. It is a burnt out comet with the asteroid designation (3200) Phaethon which swoops down to only 13 million miles of the Sun, but last year passed only 6.4 million miles from Earth. The Geminids were first seen in 1862.
The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
The area of the Geminid meteor shower radiant near the star Castor at 4 a.m. December 14, 2018. There are other very minor radiants that provide only a handful of meteors per hour. The Geminids will provide up to 120 meteors per hour. Created using Stellarium.
12/12/2018 – Ephemeris – The bright planets and a comet this week
Ephemeris for Wednesday, December 12th. The Sun will rise at 8:10. It’ll be up for 8 hours and 51 minutes, setting at 5:02. The Moon, 3 days before first quarter, will set at 10:05 this evening.
Let’s look at the bright planets for tonight. In the evening sky we have Mars still visible, but Saturn is all but lost in the bright twilight, setting at 6:22 p.m. It will pass conjunction with the Sun on New Years day. Mars will be due south at 6:30 p.m., and it will set at 12:10 a.m. Mars is moving eastward, crossing the constellation of Aquarius until the 21st, when it enters Pisces. Comet Wirtanen is moving northward, to the right of the V of stars that’s the head of Taurus the bull, and should be an excellent binocular object. On the 15th and 16th it will pass to the left of the Pleiades or Seven Sisters. Venus, our brilliant morning star, will rise at 4:19 a.m. in the east-southeast. The elusive planet Mercury will be seen below and left of Venus after it rises at 6:20 a.m.
The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addenda
Planets and the Moon
Mars, and Saturn over a Lake Michigan horizon seen at 5:45 p.m. tonight December 12, 2018. Created using Stellarium.
The waxing crescent Moon as it should appear tonight in binoculars. Created using Stellarium.
Morning planets Venus and Mercury. Jupiter is rising. December 13, 2018, 7:15 a.m.. Created using Stellarium.
Telescopic view of Venus tomorrow morning December 13, 2018. Created using Stellarium.
Planets, two comets and the Moon at sunset and sunrise of a single night starting with sunset on the right on December 12, 2018. The night ends on the left with sunrise on the 13th. Click on the image to enlarge. Comet Wirtanen is very close to opposition and to the south, so it rises after sunset and sets before sunrise. Created using my LookingUp program.
Two comets
Comet C/2018 V1 (Machholz-Fijikawa-Iwamoto) in twilight starting tonight December 12, 2018. The comet won’t climb that dramatically at 6 p.m. on the rest of the nights because the stars in the field will set 4 minutes earlier each successive evening. The latest magnitude estimate of the comet on December 15 is 7.3, two magnitudes brighter than shown here. It is just about impossible to spot in twilight. Created using Cartes du Ciel (Sky Charts).
Comet 46P/Wirtanen positions for the next week. Positions are marked with month-date and magnitude. The latest magnitude prediction for December 15th is 3.3, 5.5 magnitudes brighter than shown here. Star field position is for 9 p.m. on the 12th. Click on the image to enlarge. Created using Cartes du Ciel (Sky Charts).
12/11/2018 – Ephemeris – The Chinese just launched a spacecraft to land on the far side of the Moon
Ephemeris for Tuesday, December 11th. The Sun will rise at 8:10. It’ll be up for 8 hours and 52 minutes, setting at 5:02. The Moon, half way from new to first quarter, will set at 9:06 this evening.
Last Friday the Chinese launched their Chang’e 4 spacecraft to land on the far side of the Moon in January. That side of the Moon has been mistakenly called the dark side. It actually gets more sunlight than the near, Earth facing, side. This will be an extraordinary feat. So how can they tell what’s happening on the other side? In preparation for this landing attempt the Chinese put a communications relay satellite in a halo orbit about the Earth-Moon L2 Lagrange point 38 thousand miles (61 thousand km) beyond the Moon. It is a kind of a gravitational point of equilibrium behind the Moon. One of five, and they are very useful. The satellite will lazily orbit that point, in view of the lander and the Earth for continuous communication between the Earth and the lander.
The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Chinese mission to land a lander and rover on the far side of the Moon. Click on the image to enlarge. It’s in Chinese except the numbers. Credit China Aerospace Science and Technology Corporation via Space.com.
How Queuiao, the lunar communications satellite orbiting L2 performs its relay function. Click on image to enlarge. Credit CNSA via gbtimes.com.
Note: Next Monday’s program will be about Lagrangian points.
12/10/2018 – Ephemeris – How the star Procyon got its name
Ephemeris for Monday, December 10th. The Sun will rise at 8:09. It’ll be up for 8 hours and 53 minutes, setting at 5:02. The Moon, 3 days past new, will set at 8:09 this evening.
Visible low in the east at 9 p.m. or a little after will appear the star Procyon, sometimes called the little Dog Star. It’s in the constellation of Canis Minor, the little dog. It will rise at 8:40 p.m. for the Traverse City Interlochen area. Yet to rise at that time is the Dog Star itself, Sirius, the brightest night-time star. It won’t rise until 9:15 p.m., 35 minutes later even though Sirius is west of Procyon. I bring this up because the name Procyon means Before the Dog. At our latitude Procyon rises before any part of Canis Major, the big dog that Sirius is in the heart of. This is sensitive to one’s latitude. At the equator, say in Ecuador. Sirius would rise first due to its westerly position by 54 minutes. You see Procyon is also north of Sirius and that makes all the difference.
Note at 31 degrees north latitude they will rise together. Explain that, flat-earthers!
The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Stars and constellations in the east at 9:30 p.m., about 4 hours after sunset, on December 10th. This only works for locations above 30 degrees north latitude. Created using Stellarium.
