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2017 is a lousy year for Mars, but wait!

Throughout 2017, Mars will appear as a faint and inconspicuous reddish star in our sky. But wait until 2018, when Mars will come closer to Earth than it has since 2003.

Artist’s concept of Earth (3rd planet from the sun) passing between the sun and Mars (4th plnaet from the sun). Not to scale. At such times, Mars appears opposition the sun in our sky, and astronomers say that Mars is in “opposition” to the sun. Image via NASA.

Why is Mars sometimes bright, and sometimes faint, in Earth’s sky?

More than any other bright planet, the appearance of Mars in our night sky changes from year to year. Its wild swings in brightness are part of what make Mars a fascinating planet to watch with the eye alone. What causes these brightness changes? Mars isn’t a very big world. And it orbits the sun one step outward from Earth’s orbit. Earth takes a year to orbit the sun once. Mars takes about two years to orbit once.

The brightness of Mars changes by a lot, depending on whether Mars is close to us in its slightly larger orbit, or whether it’s far across the solar system from us.

Mars isn’t very big. That’s one reason its brightness changes so much, as the distance between Earth and Mars changes. This image compares Mars and Earth in their correct relative sizes. Mars (4,219 miles or 6,790 km in diameter) is only slightly more than half the size of Earth (7,922 miles or 12,750 km in diameter). Image via Lunar and Planetary Institute.

Mars is faint and relatively inconspicuous now and will remain so throughout 2017.

As 2017 opens, Mars is near bright Venus in the west. Venus will pass between the Earth and sun in late March, and afterwards Mars will be even less conspicuous in our western twilight sky, sitting there after sunset, far behind Earth in orbit, getting fainter and fainter and fainter.

Its superior conjunction – when it’ll be most directly behind the sun as viewed from Earth – will come on July 27, 2017.

In January 2017, Mars is falling behind Earth in the race of the planets around the sun. The distance between our two worlds is increasing, and Mars is getting fainter and fainter. Image via Fourmilab.

Mars is now a faint light in the sky – near a very bright light, Venus – in the west after sunset. On January 29, 30 and 31, people around the world will see the young moon sweep up in the west past Mars and Venus. Read more.

But, by mid-2018, Mars will appear brighter than it has in many years.

We’re relatively close – and Mars appears at its brightest in our sky for that two-year period – every time Earth passes between the sun and Mars. Astronomers call this an opposition of Mars, and it happens every two years and 50 days.

May 22, 2016 is the date Earth last went between the sun and Mars. May 30, 2016 is the date Earth and Mars last were closest. Around that time, Mars was bright in Earth’s sky. See photos of Mars in May 2016.

Throughout 2017 – and in all years lacking a Mars opposition – Mars appears faint in Earth’s sky. In non-opposition years like the current year, Mars lies far across the solar system from Earth, at times hidden from our view by the sun itself.

But Earth and Mars will keep moving in orbit. Earth will eventually catch up to Mars and pass between it and the sun again. The image below shows Mars in mid-July, 2018, when Earth will next pass between the sun and Mars.

Earth will pass between between the sun and Mars on July 27, 2018. Then, the distance between our two worlds will be at its least for this two-year period, and Mars will appear brightest in our sky. Image via Fourmilab.

This 2018 opposition of Mars isn’t an ordinary opposition. Astronomers will call it a perihelic opposition (or perihelic apparition) of Mars. The word perihelion refers the point in Mars’ orbit when it is closest to the sun. Maybe you can see that – in years when we pass between Mars and the sun, when Mars is also closest to the sun – Earth and Mars are closest. That’s what will be happening in 2018, and it’s why the Association of Lunar and Planetary Observers (ALPO) wrote:

The 2018 perihelic apparition of Mars will prove to be one of the most favorable since the 2003 apparition when the Red Planet came closest to Earth in 59,635 years (the year 57,617 BC).

According to ALPO, in 2003, Mars came within 34.6 million miles (55.7 million km) to Earth, closer than at any time in over nearly 60 thousand years! It’ll be only 1.2 million miles (just under 2 million km) farther away in 2018. Closest approach for Mars in 2018 will take place about two weeks after the opposition date, on on July 31.

So 2017 is, indeed, a lousy year for Mars. But just wait! Mars will be grand in 2018.

Diagram by Roy L. Bishop.  Copyright Royal Astronomical Society of Canada. Used with permission.  Visit the RASC estore to purchase the Observers Handbook, a necessary tool for all skywatchers.

Diagram by Roy L. Bishop. Copyright Royal Astronomical Society of Canada. Used with permission. Visit the RASC estore to purchase the Observers Handbook, a necessary tool for all skywatchers. Read more about this image.

Bottom line: Mars is bright when it and Earth are on the same side of the sun. It’s faint when it and Earth are on opposite sides of the sun. 2017 is one of the off-years, and Mars will be faint in our sky throughout this year. But, in 2018, we’ll have a grand view of Mars … best since 2003!

Deborah Byrd