(NEXSTAR) – If you look at the sky on these dark December nights, you may have noticed that the two brightest objects are sitting next to each other. Jupiter and Saturn are going to appear in the sky more than they have in 400 years.

The two planets are so close together that they appear to touch each other, separated by one-fifth the diameter of a full moon.

“They are not close in space – they are still millions of kilometers away from each other,” said NASA astronomer Henry Troop. “But… they appear to be two points very close in the sky… in fact they are so close that you can cover both planets with your pinky finger if you stretch the length of your pink arms.”

Astronomers call it a fusion when deploying celestial objects, but because it involves the two largest gas giants in our solar system, it is technically a “Excellent combination. “As the event kicks off on a holiday week, many have started calling this formation the” Christmas Star. “

There are online stories about the event Went viral, NASA responded by creating a video primer for the December 21st event. According to Troop, this event should be visible to almost anyone in the US with a clear view of the horizon.

“It is very easy to find the planets in the sky if you look up. If you can see the sunset – that means if you are in the western hemisphere in the west and southwest – you can see Saturn and Jupiter. You want to go out 45 minutes after sunset. Let the sky be a little darker. You do not have to wait until nightfall. Then look at the sunset, ”says Troop, an astronomer at NASA headquarters. “You will have about an hour to observe Saturn and Jupiter.”

Troop says that Jupiter looks like the brightest star in the sky (it’s not a star, of course it reflects the sun). Saturn will fade a little and be seen on the left side of Jupiter above.

Troop says the planets are so bright that even people in bright cities can see them and take high quality photos. If you can not build it on Monday night, he says, the two largest planets in the solar system will appear on the 20th and 22nd.

“Anyone can go out and see these planets,” Troop said.

If you plan to take pictures, NASA has created a guide Taking a photo of the best combination.

Since March 4, 1226, the nearest Jupiter and Saturn have been most visible on the 21st. There was a close reunion of the planets 400 years ago, but that event was not visible to many of us on Earth, Space.com.

On average, the best combinations take place every 19.6 years. After this month’s event, NASA says you will have to hang there until 2080 to find the next best combination of similar proximity.