Celestial Lineup Makes For A Very Bright Mars

Jul 27, 2018
Originally published on July 27, 2018 11:08 am

Updated at 7:37 a.m. ET Friday

Every two years or so, the sun, Earth and Mars line up — and that's what is happening now. It's a celestial orientation known as Mars opposition. Leaving aside any significance this might have for astrologers, from an astronomical point of view there's one thing you can say for sure about this Mars opposition: Mars will be brighter in the night sky than it's been for 15 years.

Mars is always brighter than usual during opposition. That's because from our vantage point here on Earth, the sun is shining directly at Mars. It's like pointing a flashlight directly at what you want to see. In this case, the sun is the flashlight.

But this opposition is special because of where Mars is in its orbit around the sun. That orbit is not a perfect circle. It's elliptical, slightly egg-shaped. As a consequence, there's a point in every Martian year where Mars is closest to both the Earth and the sun.

This year that happens on July 31, just a few days past opposition. On that day Mars will be only 35.8 million miles from Earth, and the closer an object is, the brighter it appears.

And even more significantly, Mars is about to reach the point in its orbit where it's closest to the sun — that's important because there is more sunlight that bounces off it, making the planet appear brighter.

There another strange thing that happens with Mars around the time of opposition. Most of the time, if you plotted the position of Mars in the night sky, it would appear to be moving eastward on successive nights. But for a few months around the time of opposition, it appears to change direction.

This strange behavior flummoxed early astronomers who thought the planets revolved around the Earth, not the sun. But it makes sense if you realize that the sun is at the center of the solar system.

This is a case where a video is worth a thousand words, or maybe 10,000 words, so if you want to understand this so-called retrograde motion, I strongly encourage you to watch the video.

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You know it's going to be a good morning when NPR science correspondent Joe Palca is here in the newsroom. Sure enough, as I was doing all this last-minute prep for the show this morning in the wee dark hours, Joe comes into the studio and looks at me and is like, Rachel, you've got to come see Mars. I mean, of course, I say, yeah, of course.

JOE PALCA, BYLINE: Yeah. You have to. I mean, you have to come see it because it's really, really bright in the sky. You could see it. You could see this little red dot. It was really amazing.

MARTIN: This little red dot. So, Joe, why can - with my naked eye see Mars?

PALCA: Well, you can see it frequently with the naked eye, but this is brighter than usual. And the reason is - there's a bunch of reasons. But the reasons are that they're - Earth, the sun and Mars are all lined up at the moment. And it's a little bit - it's not really like a flashlight, but it's a little bit like, you know, it's more like a full moon. It's like the sun is shining full on Mars. So it's the most lit up it's going to be.


PALCA: But also, it's happening at a time when Mars is closest to the sun or close to the sun. It's going to be actually closest in a little while. But that means it's getting more sunlight, so it appears brighter. So we're lined up, and we're close to the sun. And so that's why it appears so bright.

MARTIN: The sun, this big flashlight on Mars.

PALCA: That's right. It's like - well, flashlights are directed. The sun's more like a light bulb, but you get the idea.

MARTIN: (Laughter). So this happens every two years. How come that time frame?

PALCA: Well, it's because - well, the closest-to-the-sun part is more infrequent. But the two years is because Earth is taking two revolutions for every one that Mars makes because Mars is going more slowly. It's further out.


PALCA: And the other thing that happens during this period is that it's easy to send a rocket to Mars because you can get the least fuel - you need the least fuel. So last May, NASA launched a rocket to Mars, and it will arrive next November. But it's coming by right - like, right now. It's on its way. And I know what you're going to ask me.

MARTIN: You do?

PALCA: You're going to ask me, is it close to where - is it going to land near that place where they found an underground lake on Mars? And the answer is no. What were you going to ask me?

MARTIN: How did you know I was going to ask that?

PALCA: (Laughter).

MARTIN: Well, I feel like anytime we have a conversation about Mars, it always leads to - is there actually water there? Because that would mean that there's some kind of life on Mars.

PALCA: Yeah. That's the thing. I mean, every scientist will tell you, oh, we need, you know, water. It's essential for life. We've got to find it. It's important to find water. That's what's going on. The fact is finding water is great, but it doesn't prove you've got life. It just says, oh, well, one of the conditions we think is essential for life is now here. And so that's the - that's the issue with the water business.

Now, someday, they'll actually - maybe, hopefully - somebody will be able to go and look and get a sample and bring it back, put it under a microscope and see if there's something that looks like life. But right now, all the best they can do is say, I think we see water.

MARTIN: And we can see Mars.

PALCA: Yeah.

MARTIN: I mean, that's the bottom line right now.

PALCA: I mean, well, I mean, there's a certain beauty in the universe, you know.

MARTIN: Isn't there? We all deserve more.

PALCA: We get to see it.

MARTIN: We all deserve beauty and wonder, which NPR's Joe Palca brings to us. Thanks so much, Joe.

PALCA: You're welcome. Transcript provided by NPR, Copyright NPR.