What's Up - January 2021

What's Up for January? Getting close to the Sun, some easy outer-planet spotting, and a chance to catch quick-moving Mercury.

The new year begins with planet Earth at the closest point in its orbit around the Sun, called perihelion, on January 2nd. Now you may have learned in school that Earth orbits a certain distance from the Sun and that its orbit is nearly circular. The average distance from Earth to the Sun is called an astronomical unit, but since our orbit is not a perfect circle, it means sometimes we're a bit closer to the Sun, and sometimes farther away.

In fact, our distance from the Sun varies by around 3 million miles over the course of the year. That's nearly 13 times the distance from Earth to the Moon.

At perihelion, Earth will be about 91.5 million miles from our local star. And when we're at the farthest point, it's called "aphelion." That happens this year on July 5th, when we'll be about 94.5 million miles away.

If you have access to binoculars or a telescope, then you might want to haul them out on January 20th, which offers an easy opportunity to view the planet Uranus. The distant, outer planet is too faint for most of us to see with the unaided eye, and it can be tough to locate in the sky without a computer-guided telescope. But on the 20th, Uranus will be located right between the Moon and Mars. That evening, find the crescent Moon and the Red Planet in the couple of hours after it gets dark. Scan your way over from Mars toward the Moon, and you should be able to find the faint, bluish disk of Uranus.

Along with Neptune, Uranus has only been visited by a single spacecraft so far, that being NASA's Voyager 2, more than 30 years ago. And as more recent telescope views have revealed the active atmosphere beneath its hazy, blue exterior, scientists are eager to one day return for a closer look.

The last two weeks of January offer opportunities to catch a glimpse of the fast-moving planet Mercury. Look for the innermost planet of our solar system just after sunset beginning mid-month. You'll need a clear view toward the west, as Mercury will appear just a few degrees above the horizon (about the width of your outstretched fist).

This little planet orbits much closer to the Sun than Earth, meaning it also goes around the Sun much faster, completing its "year" in about a quarter of the time it takes Earth to go around once. And that's why we have a chance to view Mercury in the sky every three months or so, as it appears to dart back and forth from one side of the Sun to the other. But Mercury never gets too far away from the Sun from our vantage point, and thus we only see the little 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 slated to see a new visitor in orbit in 2025, when the joint European and Japanese mission BepiColombo arrives there.

Here 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.