In a rare celestial event, the two brightest planets in our solar system will appear so close together that it will look as if they are almost touching.

On Friday they'll be joined by the faintest sliver of a crescent moon. And Mars will be coming to the party too, keeping close to its fellow planets in the morning sky and putting four celestial orbs in one place at the same time.

But the main event and the thing that has our local astronomy community particularly excited is the Jupiter-Venus conjunction – or, more poetically, the "dance of the planets".

But it won't last long.

Beginning about 5.15am (5.45 in Melbourne) there will be a brief window to see the dance, says David Reneke, editor of Astro-Space News.

On Friday at 5.42 the sun will break through the horizon (5.58 in Melbourne), its brightness almost immediately obscuring the planets. Each subsequent night the planets' orbits will carry them across the sky, further and further away from each other.

Mr Reneke advises aspiring viewers to find an elevated vantage point with a clear view of the horizon, and look east.

Mars will also appear in the same section of the sky, he said.

"If you ever wanted to find where Mars and Jupiter were, this is a night where you won't need to go searching for them," he says.

"You don't need binoculars or telescopes to do astronomy, you just get up and have a look."

They'll appear so close, you should be able to just slide an outstretched thumb between them.

Conjunctions happen when the orbits of Earth and other planets converge in such a way that it appears as if they're lining up, despite being separated by billions of kilometres.

In this case, despite Venus being closer to the Sun than Earth and Jupiter being much further away, it will look as if they are in almost the same spot in our sky.

Each planet in the solar system follows a different orbit at a different speed. The gas giant Jupiter, for example, takes almost 12 years to orbit the sun; Venus does a lap in just 225 days.

About once a year those differing speeds will put them in what looks from Earth like orbital alignment.

What makes this year's conjunction special is how close the two planets will come in our sky; there is likely to be only one repeat performance in the next hundred years.

Early risers on Friday who look to the skies between 3 and 5am will be rewarded with an even better view – the Earth will pass through the debris field of an old comet, parts of which will burn up in the earth's atmosphere, producing as many as 20 shooting stars an hour, astronomers predict.

Mr Reneke says he has previously received worried phone calls when planetary conjunctions were looming.

"There used to be a lot of hype – people would say the combined gravity of all the planets would cause earthquakes," he laughs.

This is not something sinister or dangerous, he says. "It's just luck."