Close encounter with Mars

By Jennifer Ennion 2 May 2016
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This month, Earth is going to get up-close and personal with the red planet, and Australians are particularly well placed to see it.

KEEP YOUR FINGERS crossed for clear skies this month, as Mars reaches the nearest point to Earth in its orbit. The planet will be noticeably red and outshine any stars, as it makes its “close approach” on Monday, 30 May.

The event happens approximately every 26 months, and this year Australians will be in prime position to see the planet. That’s because Mars will be in the constellation Scorpius, meaning it will be south of the Equator and high in the sky. And the higher it is in the sky, the brighter it appears.

Associate Professor Jonti Horner, an astronomer at University of Southern Queensland, says it’s a good time to look up.

“This one’s particularly good for us in the Southern Hemisphere because it’s a combination of a relatively close encounter, coupled with Mars being almost ideally located to be high in the sky for Australian observers,” says Jonti.

One of the great things about Mars’s close approach is it’s not over in one evening. Mars will be putting on an impressive show for several weeks, brightening slowly and then gradually fading as Earth pulls away. The best period, however, will be from about 18 May  to 3 June. That said, for Australians, Mars will be almost overhead at midnight on 22 May, when it’s opposite the Sun. The planet will also be significantly brighter than any stars, and we’ll be able to see its red colour – but if you want to see any features you’ll need a telescope.

Mars myths

Although viewing will be great, don’t expect Mars to be as big as the Moon – that’s a popular hoax that spreads on social media every time its close approach comes around.

Still, there is some truth behind it, says Jonti.

“In one way it’s right. Mars is larger than the Moon but it’s not larger than the Moon in the sky, it’s larger than the Moon where it is in space.”

In short, as we look up at the sky, Mars won’t appear as big as the Moon.

Observing Mars

Despite this year’s top viewing opportunity, it does in fact get better. Viewing is at its best every 15 or so years, and this is because Mars and Earth travel at different speeds and therefore have different orbital periods. Earth travels around the Sun every 365 days, while Mars is further away from the Sun and takes 686 days.

The next close approach will be on 31 July, 2018, when Mars will be nearer to Earth and appear even brighter. A particularly good year for observing was back in 2003, and it won’t be as impressive again until about 2287.

It’s all down to orbital timing, Jonti says. “It’s just like rolling dice. You’ll eventually land on that point.

“That’s the time where we get the kind of perfect storm of the Earth passing Mars on the inside, whilst at the same time Mars is near perihelion (the orbital point when it’s nearest the Sun).”

Not every close approach is the same, because the distance between Mars and Earth changes each time. This is partly because Mars and Earth have elliptical orbits, and Mars’s orbit is longer. For us, this means the brightness of Mars varies.

What to remember:

  • Mars will be closest to Earth on 30 May (at a distance of about 75 million kilometres);
  • It will be opposite the Sun on 22 May;
  • It will reach its highest point around midnight;
  • The best time for viewing will be from about 18 May  to 3 June;
  • Mars’s close approach occurs roughly every 26 months.