If you enjoyed looking at Jupiter and Saturn’s great conjunction last month, you’re in for another stargazing treat. Those planets are now joined by Mercury -- and you can see all three together just after dusk this weekend.
On December 21, although the planets were hundreds of millions of miles apart, Jupiter and Saturn appeared just a tenth of a degree apart -- roughly the thickness of a dime held at arm’s length, NASA explains. Since then, they have slowly drifted apart.
Now, however, Jupiter and Saturn have been joined by Mercury to form a small triangle visible just above the horizon after sunset through January 11. It’s the first time since October 2015 that three planets have appeared so close together.
Here’s why this type of alignment happens so infrequently: Jupiter’s orbit of the sun takes 11.86 years, while Saturn’s orbit takes 29.46 years. Mercury, the planet closest to the sun, takes just 88 days to complete its orbit.
When To See The Planets
A planetary trio occurs when three planets fit within a circle with a diameter less than five degrees in width, EarthSky explains. To put this in perspective, three fingers held together at an arm’s length approximates five degrees, EarthSky continues.
The planets will all be visible tonight within an area less than 2.5 degrees, Astronomy magazine reports. Mercury will be the lowest of the three in the sky, Jupiter will be the brightest, and Saturn will be the dimmest.
The best time for seeing the planets at their closest is tonight at 19 UTC (Coordinated Universal Time), EarthSky reports. You can convert UTC to your local time here.
Another option is to use Stellarium’s online app to determine where and when to look for the planets at your specific location. You can also find Mercury, Jupiter, and Saturn’s setting times in your location using the Old Farmer’s Almanac or TimeandDate.com.
How To See The Planets
Fortunately, the planets will be large and bright, making them easier to see. Jupiter is about 2.5 times brighter than Mercury and 10 times brighter than Saturn. Mercury is approximately four times brighter than Saturn, EarthSky notes.
Your best chance for viewing the planets requires an unobstructed view of the west-southwest horizon, no later than 30 minutes after sundown. While all three planets are bright, the afterglow of sunset may make it difficult to locate the planets, so plan on using binoculars. All three planets will be in your field of view simultaneously.
Given that this is January, be prepared to bundle up. Dress in layers, and you may want to use a blanket or sleeping bag if you plan to be outside for long.
If you enjoy looking at a planetary trio or miss this one, there’s good news. Mercury, Jupiter, and Saturn is only the first planetary trio of this year. On February 13, Mercury, Venus, and Jupiter will be visible simultaneously, according to Space.com.