5 planets visible at once for 1st time in a decade

For the first time in more than a decade, you have the rare opportunity to spot five planets in the night sky at the same time.

Mercury, Venus, Mars, Jupiter and Saturn are the planets in our solar system that are visible with the naked eye. (Uranus and Neptune are only visible with telescopes.) The five bright planets line up across the sky before dawn for the next month, until around Feb. 20.

The last time that happened was between mid-December 2004 and mid-January 2005.

"Not many people have seen all five naked [eye] planets and at the same time," said Randy Attwood, executive director of the Royal Astronomical Society of Canada. "Usually, they're visible at different times of the night."

And most of the time, he added, some of them are not visible. That happens when they're on the opposite side of the sun relative to Earth.

Viewing tips

So how can you spot this rare sight?

Start by setting your alarm for about an hour before dawn so you can get up in time to see it.

Attwood recommends going somewhere like a park with a good view of the south-southeast horizon. Mercury will appear generally very low in the sky and will only be visible for a short time near sunrise, as it's close to the sun.

"You have to have a pretty clear sky and low horizon — no trees or buildings," he said.

It is currently rising earlier and higher each night, and is expected to be easier to see around Feb. 5 or 6 when it's at its farthest from the sun, from our perspective.

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Attwood recommends using a star chart from an astronomy website or an app such as Sky Safari to help you figure out where to look for and find each planet.

"They're not in the same part of the sky by any means," Attwood said. Nor are they in the order of their distance from the sun.

It will be easiest to find Venus — the brightest object in the night sky after the moon — and Jupiter, which is also brighter than the brightest stars.

Saturn will be about the same brightness as the brightest stars, Attwood added, and Mars is currently a bit dimmer, although it will brighten over the course of the month.

Not sure if you're looking at a star or a planet? Here's how you can tell the difference, Attwood says: "Planets don't twinkle."

If you miss this window, the planets will actually align again later this year — in August. But at that point, they'll be visible in the evening sky, and Mercury and Venus will be too low in the sky to see easily from northern latitudes, the astronomy website EarthSky warns.

The Southern Hemisphere will get a better view. After that, the next viewing of five planets at once isn't until October 2018.

Why it's a rare sight

Why is it so rare for the planets to show up in the night sky at the same time?

It has to do with how quickly they move around the sun and where they are in their orbit relative to Earth, Attwood says.

When they're on one side of the sun, they appear in the evening, when they're on the other side of the sun, they appear in the morning, and when they're behind the sun, we can't see them at all.

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The length of time it takes each planet to complete its orbit varies widely — from 88 days for Mercury to 29 years for Saturn. That means they are rarely all on the same side of the sun, relative to Earth, at the same time.