At last, Mars’s great opposition is upon us—October 13, 2020! This week, the Red Planet will appear bigger and brighter than it will be in years. Not only is Mars brighter than any star in the sky, it’s even brighter than Jupiter, which is unusual. Moreover, Jupiter is 22 times bigger than Mars in terms of diameter! And more than twice as shiny. See viewing details.
For the last couple weeks, the Red Planet has been growing brighter as it slowly approached a state that astronomers call opposition—when Mars and the sun are on opposite sides of Earth.
What Is the Mars “Opposition”
Earth passes between the sun and Mars today at around 23:00 UTC (7 p.m. EDT, 6 p.m. CDT, 5 p.m. MDT and 4 p.m. PDT).
During opposition, Mars and the Sun are on directly opposite sides of Earth. Because of this, Mars appears positioned closest to Earth. Earth and Mars have converged for a close encounter!
Bottom-line: this means Mars will appear bigger than usual—so the Red Planet is easy to see!
Opposition is a fantastic time to observe Mars because we usually can’t see the Red Planet very well with the naked eye; it appears dim and small. Oppositions of Mars happen every 26 months. Because planetary orbits are elliptical, not all oppositions are the same. An opposition can occur anywhere along Mars’ orbit. This year, Mars opposition on October 13, 2020 is especially good.
The only thing that can make Mars look brighter than ol’ Jove, despite the latter’s many advantages, is if it comes extraordinarily close to us. (Its closest point, which always happens around the date of opposition, was October 6.) During this week, Mars is only 37 million miles away, which is close in the scheme of the universe!
How Big Will Mars Appear?
Though the Red Planet is just half the size of Earth, it manages to appear 23 arcseconds in width.
Whoa, slow down. Arcseconds?
Yes, astronomers measure the size of celestial objects by their diameter in arcseconds and arcminutes. One degree is sixty arcminutes.
The Moon appears half a degree wide, so it’s thirty arcminutes. That’s huge compared to the apparent size of far-away planets. No planet appears as big as even a single arcminute, though Venus occasionally comes close. So we must slice up each arcminute into 60 arcseconds in order to accurately measure the size of our fellow planets.
During October’s opposition, Mars will have an apparent disk size of 23 arcseconds. We won’t see Mars exceed this size until 2035.
Mars’ size in “arcseconds” during past and future oppositions. Credit: Pete Lawrence
Having trouble visualizing it all? A single arcsecond is the size of a dime that is 2 ½ miles away. A very small looking circle.
Jupiter typically appears about 40 arcseconds in width.
Mars, when it comes close to us every 26 months, has an opposition width of 14 to 25 arcseconds. The word on the street among astronomers is that it needs to be at least 20 arcseconds to show nice detail in backyard telescopes. The good news is that this week, Mars is 23 arcseconds across.
Why the variation? Well, Earth travels faster than Mars so that we pass it like passing a truck on the highway every two years and two months. But since we have a fairly round orbit while the Martian path around the Sun is oval or lopsided, the gap between our orbits can be narrow, like it was when we passed it in 2003, or wide, like during the Martian opposition of 2012.
If we happen to pass Mars on August 28, we meet it as its closest possible distance. That’s when it shows us a 25 arcminute disk. That actually happened in 2003—the nearest visit of Mars in 60,000 years. This time around, meeting it in early October, we are not too far from that date, so the opposition is a good one, with the Red Planet 23 arcseconds in diameter.
This means two things …
Viewing Tips to See Mars
If you don’t have a telescope, just look around for the brightest orange star in the whole sky. Mars will be out all night long, which is what we expect during any opposition.
Mars rises low in the east at sunset/nightfall. That fiery dancing dot is brighter than all the stars.
The Red Planet is highest around midnight in the south.
Then Mars appears lowish in the west as it sets around dawn.
If you do own a telescope, choose a night when the stars aren’t twinkling. Then gaze at Mars using a magnification of at least 100x. You’ll see its southern polar cap—made of dry ice. And you’ll see lots of dark surface features, looking like dusky smudges. Very cool.
Credit: J. Westlake/NASA
During the next Martian oppositions, the Red Planet (which isn’t really red, but orange) will be 17 arcseconds in 2022, 14.5 arcseconds in 2025, 14 arcseconds in 2027, 14.5 arcseconds in 2029, 17 arcseconds in 2031, and 22 arcseconds in 2032. So you’ll be significantly older and wiser before Mars again looks this big, and shows this much detail in telescopes.
We pass it quickly, and Mars will lose half its light by mid-November. So catch it now, the next clear night. Grab that friend who has a telescope and watch Mars. And don’t expect anything big. It’s very cool, but, still, 23 arcseconds is not the Goodyear blimp.