What are the highlights of sky observation in January 2021? Mark the closest approach to Earth’s Sun for the year, called perihelion, at the start of the month, then spot a few elusive planets: Uranus on January 20 and Mercury throughout the second half of the month.
Additional information on the topics covered in this episode of What’s Up, as well as stills from the video and the transcript of the video, can be found at https://solarsystem.nasa.gov/whats-up-skywatching -tips-from-nasa.
Credit: NASA / JPL-Caltech
What’s new for January? Get closer to the Sun, easily spot outer planets, and have a chance to catch fast moving Mercury.
The New Year begins with planet Earth at the point closest to its orbit around the Sun, called perihelion, on January 2. Now you may have learned in school that the Earth rotates a certain distance from the Sun and its orbit is almost circular. The average distance between the Earth and the Sun is called an astronomical unit, but since our orbit is not a perfect circle, it means that sometimes we are a little closer to the Sun, and sometimes further.
In fact, our distance from the Sun varies by about 3 million kilometers during the year. This is almost 13 times the distance between Earth and the Moon.
At perihelion, Earth will be approximately 91.5 million kilometers from our local star. And when we are at the farthest point, it is called “aphelion”. This is happening this year on July 5, when we will be approximately 94.5 million kilometers away.
If you have access to binoculars or a telescope, you might want to carry them on January 20, which provides an easy opportunity to see the planet Uranus. The distant, outer planet is too faint for most of us to see with the naked eye, and it can be difficult to locate it in the sky without a computer-guided telescope. But on the 20th, Uranus will be located just between the Moon and Mars. That evening, find the crescent moon and the red planet within two hours of dark. Scan your path from Mars to the Moon, and you should be able to find the pale, bluish disk of Uranus.
Along with Neptune, Uranus has only been visited by one spacecraft so far, NASA’s Voyager 2, over 30 years ago. And as more recent telescope views have revealed the active atmosphere beneath its hazy, blue exterior, scientists are eager to return one day for a closer look.
The last two weeks of January provide an opportunity to glimpse the rapidly moving planet Mercury. Look for the innermost planet in our solar system just after sunset from mid-month. You will need a clear view to the west, as Mercury will appear a few degrees above the horizon (about the width of your outstretched fist).
This tiny planet orbits much closer to the Sun than to Earth, which means it also circles the Sun much faster, completing its “year” in about a quarter of the time it takes Earth to do so. the turn once. And that is why we are fortunate enough to see Mercury in the sky every three months or so, as it seems to come and go from one side of the Sun to the other. But Mercury never moves too far from the Sun from our point of view, so we only see the small planet just before or after sunrise or sunset.
Last visited by NASA’s MESSENGER spacecraft, which completed its mission in 2015, Mercury is expected 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 follow 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 happening this month.