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SPACE

Planet Parade

January 19th, 2016

Image credit: USA Today/Earthsky.org

by Jason Kendall

For the next two weeks, you’ll be able to see the five planets closest to us all lined up … without a telescope!

Mercury, Venus, Saturn, Mars and Jupiter will all be on parade for you to see. But you’ll have to get up early!

How’s this possible?

Usually, the most obvious things you see in the sky are the Moon and the Sun. Lots of stars too in the night sky.

So, where are all the planets?

Some of the stars in the sky are actually planets. In fact, there are five of them that you can see without a telescope or binoculars: Mercury, Venus, Mars, Jupiter and Saturn.

The rest you need telescopes for because they’re too far away.

So how do I know which stars are actually planets?

The answer is that the word “Planet” is a really old word. It comes from ancient Greek, and it means “Wanderer.” In Greek, we would spell it πλανήτης (planētēs).

What does wandering have to do with anything?

The planets are the wandering stars. All of the other stars seem to stay fixed on the sky, and you always see them in the same place with respect to each other. They all rise and set, and as they do, you’ll notice as you get older that the same stars are visible in January nights as the years go on. But the planets move. They actually change position in the sky with respect to all the other stars. We now know that they orbit the Sun, so they have to change position, and we also know that the distant stars are so far that we can’t see their changes within a full human lifetime. So the only things we’ll see move are the planets.

So, how can you see them?

For the next few weeks it happens that all five of the Classical Planets known to everyone for thousands of years in the pre-dawn sky are positioned in their orbits around the Sun just perfectly so that we can see Jupiter, then Mars, then Saturn, then Venus, then Mercury rising in the East before the Sun. Venus is the brightest one, brighter in the sky than any star (other than the Sun of course!), followed by Jupiter.

So, if you want to make sure you know if you’re getting it right, Venus and Jupiter are still visible when the sun starts to rise, and the sky is getting blue. Then, once you know those two, look for Mars, which actually looks red. Saturn is yellow-ish and ruddy. Mercury will be your biggest challenge. You can use a sky chart, like one provided by Sky and Telescope .

Any tips?

One good way to know that you’re actually looking at a planet is the following: close one eye and put your hand at arms-length away. Slowly pass your thumb at arms-length with one eye closed over a star. You’ll see that the star “winks” out, meaning it just blinks out when you pass your thumb over it. But, when you do the same with a planet, it FADES or DIMS out. It’s just like passing your thumb across a streetlight a mile away. It’ll seem to dim out as you cover more and more of the streetlight. This is one way to know if it’s a planet. The better way is to watch the skies night after night, and see which stars move; those are the planets.

This is a really cool opportunity that hasn’t happened since 2005, possibly the first time since you’ve been alive. So, get up a bit early and keep your eye to the sky!

Jason Kendall is the Astronomy liaison and an adjunct professor at William Paterson University in New Jersey. Thanks for making Space understandable and interesting, Jason!

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