What are some of the highlights of skywatching in January 2021? At the beginning of the month, mark the closest approach from Earth to the Sun for the year, called perihelion, and then spot a few elusive planets: Uranus on January 20 and Mercury during the second half of the month.
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What’s for January? Get close to the sun, easily spot the outer planet, and a chance to catch fast-moving Mercury.
The new year begins with planet Earth at the closest point in its orbit around the sun, called perihelion, on January 2. Now you may have learned in school that the Earth rotates at a certain distance from the sun and that its orbit is almost circular. The average distance from the Earth to the sun is called an astronomical unit, but since our orbit is not a perfect circle, this means that we are sometimes closer to the sun, and sometimes further away.
In fact, our distance from the sun varies by about 3 million miles during the year. That is almost 13 times the distance from the Earth to the Moon.
At perihelion, Earth will be about 147.5 million miles from our local star. And when we are at the farthest point, it is called “aphelion”. That will happen this year on July 5, when we are about 94.5 million miles away.
If you have access to binoculars or a telescope, you may want to haul them out on January 20, which provides an easy opportunity to view the planet Uranus. The distant outer planet is too dim for most of us to see with the naked eye, and it can be difficult to locate in the sky without a computer-controlled telescope. But on the 20th, Uranus will be exactly between the moon and Mars. That evening, find the crescent moon and the red planet in the few hours after dark. Scan your way from Mars to the moon and you should be able to find Uranus’ faint, bluish disk.
Together with NeptuneUranus has only been visited by one spacecraft so far, that being NASAVoyager 2, more than 30 years ago. And since more recent telescope images have revealed the active atmosphere beneath its hazy, blue exterior, scientists want to return one day for a closer look.
The last two weeks of January offer opportunities to glimpse the fast-moving planet Mercury. Look for the innermost planet of our solar system just after sunset which starts mid-month. You need a clear view to the west as Mercury will appear only a few degrees above the horizon (about the width of your outstretched fist).
This small planet orbits much closer to the sun than the Earth, which means it also revolves around the sun much faster, completing its ‘year’ in about a quarter of the time it takes for Earth to go around once. And that’s why we have the chance to see Mercury in the sky about every three months, as it appears to be darting back and forth from one side of the sun to the other. But Mercury never gets too far from the sun from our point of view, so we only see the small planet just before or after the sun rises or sets.
Last visited by NASA’s MESSENGER spacecraft, which ended its mission in 2015, Mercury is scheduled to see a new visitor in orbit in 2025, when the joint European and Japanese mission BepiColombo arrives there.
These are the phases of the moon for January.
You can catch up on all of NASA’s missions to explore the solar system and beyond at nasa.gov. I’m Preston Dyches from NASA’s Jet Propulsion Laboratory, and that’s what’s up for this month.