Jupiter and Saturn join in the night sky in 'great conjunction.' Here's how you can see it

If you have a keen eye, you may have noticed two fairly bright objects resembling stars low in the western sky after sunset inching closer together over the past month. But those aren't stars: they're two planets, Jupiter and Saturn. On Dec. 21 — the day of the winter solstice — the two will be so close together they'll almost seem to touch.

Jupiter and Saturn — the largest planets in our solar system — have been visible in the sky since spring, with Jupiter being the brighter of the two; it is also the second-brightest planet in the sky after Venus. In the summer, the pair were high in the south, but over the past few months, they've been getting closer and closer, and lower in the southwestern sky.

Astronomers call close pairings of astronomical objects conjunctions. And this conjunction of the two planets is the closest since 1623, making it a "great conjunction" — though that event wasn't visible as they were too close to the sun.

The last time the pair were observed to be this close was in 1226, almost 800 years ago, a time when Ghengis Khan's rule was coming to an end.

How to find them

Astronomers measure the distance between two objects in the sky using degrees. Right now, the two planets are roughly 0.7 degrees apart. But on Dec. 21, they will be a mere 1/10th of a degree apart.

You can measure their close approach over the coming days with your own fingers. Using your pinky finger held at arm's length is a rough measure of one degree of separation. 

To find the two planets, you'll need a good view of the southwestern horizon shortly after sunset. And while you don't need any equipment to view it, if you have a pair of binoculars, you'll be able to tease them apart. Viewers with telescopes will get a rare chance to capture the pair in a single field of view.

December isn't exactly a great time to catch astronomical events as it is one of the cloudiest months of the year across the country. So if you can't watch the event on Dec. 21, there are some options to see it online.

If the skies are clear in Toronto, York University's Allan I. Carswell Observatory will host a live online event. 

In Arizona, where there's a better chance of clear skies, the historic Lowell Observatory will also be hosting a live online event.