Watch Jupiter, Venus & Mars Form a Cosmic Trio This Week

If you've seen two bright stars close to each other in the early hours of the morning, you've just seen Jupiter and Venus. If you'll look more closely, you may spot Mars somewhere below Jupiter.

This phenomenon is visible until Thursday and won't happen again until 2021, due to the differing speed at which all three planets travel around the sun.

As the week progresses, you'll find all three planets will move closes to each other, until they form "a very close triangle in the sky on Wednesday morning," Mashable said.

"You won't need any special equipment to spot the planetary conjunction - the astronomy term for a close grouping of objects in the sky," the news site said. "The two planets are some of the brightest objects in our skies, and they look like gleaming stars."

Among the three, Venus is the brightest, with Jupiter coming in second and Mars a faint third. You may even spot Mercury somewhere below Mars just as dawn breaks.

This planetary trio is said to be a rare sight, considering the differing orbits of the three planets.

"Venus takes only a fraction of one Earth year - 225 days - to orbit the sun once," MailOnline pointed out. "Jupiter takes about 12 Earth years - 4,330 days - to go round the sun, while Mars takes 686 days."

"Mars in now just 33.9 million miles from Earth, Venus is just over 56 million miles and Jupiter about 10 times further at 560 million miles (900 million km)," the British publication added.

"As Jupiter is rising higher in the sky, having just come out from behind the Sun at the end of last month - and the same with Mars - as they move further along in their orbits they catch up with Venus, which has pretty much reached the furthest point of its orbit before it starts coming back in towards the Sun again," University of Adelaide's Ian Musgrave told ABC Australia. "So they'll come very close to each other because of orbits of the planets are mostly in the same plane.

"They can get very, very close or moderately close and in this particular case if you've been up at about five o'clock in the morning, you'll have been able to see Venus and Jupiter strung out in a line just above the horizon," he added. ""The distance between them was about the distance of a finger held out at arm's length."

Further, Saturn will also be visible this month, albeit at night.

"At northerly latitudes, Saturn sets at early evening in early October and as night is falling by the month's end," EarthSky said. "From the Southern Hemisphere, Saturn stays out a bit later, setting at mid-to-late evening in early October and early evening in late October."

WATCH: