Tonight – January 6, 2015 – the dazzling starlike object close to the moon, as seen from around the world, is the giant planet Jupiter. The moon rises first, a couple of hours after sunset, and Jupiter follows the moon into the sky roughly an hour later. The exact rising times for the moon and Jupiter vary around the world, but you can’t miss this pair in clear skies by late evening tonight (say, by about 11 p.m. or later), no matter where you are on Earth. Tomorrow evening’s pairing of Jupiter and the moon will be even closer.
What motions of the moon and Jupiter cause them to come together this way in our sky? There are several motions to notice. First, the moon’s orbital motion carries it near Jupiter each month. Earth’s spin under the sky causes the moon and Jupiter to move westward in the course of a single night. And Jupiter is moving, too, in front of the stars.
Notice the moon’s orbital motion.
Notice Earth’s spin under the sky.
Notice the moon’s orbital motion. It’s easy. Just look at the moon and Jupiter tonight (Tuesday night or Wednesday morning). Then notice them again tomorrow night (Wednesday night or Thursday morning). You’ll see by tomorrow evening that the moon has moved closer to Jupiter on the sky’s dome. That change is due to a true motion of the moon itself, its motion through space in orbit around Earth.
Due to its orbital motion, the moon travels about 13o eastward in front of the backdrop stars every day. For reference, the moon’s diameter equals one-half degree.
Notice Earth’s spin under the sky. Meanwhile, in course of a single night, the moon and Jupiter go westward across our sky. They do so for the same reason that the sun goes westward during the day … because the Earth rotates from west-to-east on its axis. Earth’s spin causes the sun, moon, planets and stars to appear to move from east to west on a daily basis.
So watch for Jupiter this evening or tomorrow evening. They will be in the east. Then, if you’re up early tomorrow morning (Wednesday) or the following morning (Thursday), look for the moon and Jupiter in the west before sunrise. This motion in the course of one night is due to Earth’s spin.
Looking west before sunrise on Wednesday, January 7. If you’re up before dawn, you may also see Regulus, the brightest star in the constellation Leo the LIon
Jupiter is moving, too. Jupiter’s own motion in orbit around our local star, the sun, causes this world to change its position in front of the background stars as seen from Earth. In contrast to our nearby moon, Jupiter moves at a snail’s pace in front of the stars. Sometimes, it seems to move erratically, a fact that baffled the ancient stargazers.
It moves more slowly than our moon in front of the stars because it is much farther from us than the moon.
It moves erratically because we view Jupiter from the platform of a moving Earth. Our motion in orbit causes Jupiter to appear to move backwards (westward, or retrograde) in its orbit for about four months every year. Really, this backwards motion is an illusion. It happens because Earth moves faster than Jupiter in orbit. It’s like we’re in a fast car, passing a slower car on the highway. For a time, the slower car appears to move backwards in front of the distant landscape. That’s the case with Jupiter now. We’ll soon pass between Jupiter and the sun. Jupiter has been moving in a retrograde fashion – westward in front of the stars – since December 9, 2014.
We’ll pass between the sun and Jupiter on February 6, 2015.
Jupiter will end its retrograde motion, and begin moving eastward in front of the stars again, in early April, 2015.
Not too late. Order your 2015 EarthSky Lunar Calendar today!
Jupiter is central to its own system of 66 (or 67) moons. Here is a hypothetical future base on Jupiter’s icy moon Europa. Image via FlyingSinger on Flickr.
Believe it or not, Jupiter’s orbital speed (13 kilometers/second) is much faster than the moon’s (1 km/second). Keep in mind, though, that far-distant Jupiter takes nearly 12 years to circle the sun in its great big orbit. On the other hand, our moon circles the Earth in its tiny orbit in less than four weeks.
By the way, unlike the stars, the moon and Jupiter don’t shine by their own light. They shine by reflecting the light of the sun.
Bottom line: Look for two brilliant beauties – the moon and the planet Jupiter – close together for several nights. The moon is edging toward Jupiter on January 6, 2015 and even closer on January 7. Their close proximity on the sky’s dome will be visible throughout the world.
January 2015 guide to the five visible planets
from EarthSky http://ift.tt/1tCxlgY
Tonight – January 6, 2015 – the dazzling starlike object close to the moon, as seen from around the world, is the giant planet Jupiter. The moon rises first, a couple of hours after sunset, and Jupiter follows the moon into the sky roughly an hour later. The exact rising times for the moon and Jupiter vary around the world, but you can’t miss this pair in clear skies by late evening tonight (say, by about 11 p.m. or later), no matter where you are on Earth. Tomorrow evening’s pairing of Jupiter and the moon will be even closer.
What motions of the moon and Jupiter cause them to come together this way in our sky? There are several motions to notice. First, the moon’s orbital motion carries it near Jupiter each month. Earth’s spin under the sky causes the moon and Jupiter to move westward in the course of a single night. And Jupiter is moving, too, in front of the stars.
Notice the moon’s orbital motion.
Notice Earth’s spin under the sky.
Notice the moon’s orbital motion. It’s easy. Just look at the moon and Jupiter tonight (Tuesday night or Wednesday morning). Then notice them again tomorrow night (Wednesday night or Thursday morning). You’ll see by tomorrow evening that the moon has moved closer to Jupiter on the sky’s dome. That change is due to a true motion of the moon itself, its motion through space in orbit around Earth.
Due to its orbital motion, the moon travels about 13o eastward in front of the backdrop stars every day. For reference, the moon’s diameter equals one-half degree.
Notice Earth’s spin under the sky. Meanwhile, in course of a single night, the moon and Jupiter go westward across our sky. They do so for the same reason that the sun goes westward during the day … because the Earth rotates from west-to-east on its axis. Earth’s spin causes the sun, moon, planets and stars to appear to move from east to west on a daily basis.
So watch for Jupiter this evening or tomorrow evening. They will be in the east. Then, if you’re up early tomorrow morning (Wednesday) or the following morning (Thursday), look for the moon and Jupiter in the west before sunrise. This motion in the course of one night is due to Earth’s spin.
Looking west before sunrise on Wednesday, January 7. If you’re up before dawn, you may also see Regulus, the brightest star in the constellation Leo the LIon
Jupiter is moving, too. Jupiter’s own motion in orbit around our local star, the sun, causes this world to change its position in front of the background stars as seen from Earth. In contrast to our nearby moon, Jupiter moves at a snail’s pace in front of the stars. Sometimes, it seems to move erratically, a fact that baffled the ancient stargazers.
It moves more slowly than our moon in front of the stars because it is much farther from us than the moon.
It moves erratically because we view Jupiter from the platform of a moving Earth. Our motion in orbit causes Jupiter to appear to move backwards (westward, or retrograde) in its orbit for about four months every year. Really, this backwards motion is an illusion. It happens because Earth moves faster than Jupiter in orbit. It’s like we’re in a fast car, passing a slower car on the highway. For a time, the slower car appears to move backwards in front of the distant landscape. That’s the case with Jupiter now. We’ll soon pass between Jupiter and the sun. Jupiter has been moving in a retrograde fashion – westward in front of the stars – since December 9, 2014.
We’ll pass between the sun and Jupiter on February 6, 2015.
Jupiter will end its retrograde motion, and begin moving eastward in front of the stars again, in early April, 2015.
Not too late. Order your 2015 EarthSky Lunar Calendar today!
Jupiter is central to its own system of 66 (or 67) moons. Here is a hypothetical future base on Jupiter’s icy moon Europa. Image via FlyingSinger on Flickr.
Believe it or not, Jupiter’s orbital speed (13 kilometers/second) is much faster than the moon’s (1 km/second). Keep in mind, though, that far-distant Jupiter takes nearly 12 years to circle the sun in its great big orbit. On the other hand, our moon circles the Earth in its tiny orbit in less than four weeks.
By the way, unlike the stars, the moon and Jupiter don’t shine by their own light. They shine by reflecting the light of the sun.
Bottom line: Look for two brilliant beauties – the moon and the planet Jupiter – close together for several nights. The moon is edging toward Jupiter on January 6, 2015 and even closer on January 7. Their close proximity on the sky’s dome will be visible throughout the world.
January 2015 guide to the five visible planets
from EarthSky http://ift.tt/1tCxlgY
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