Bad Astronomy
The entire universe in blog form

Feb. 19 2015 7:00 AM

Close Encounter of the Stellar Kind

Seventy thousand years ago, a pair of stars gave our solar system a close shave. But if you had been around for it, you wouldn’t even have noticed.

The stars are a part of a binary system found by astronomer Ralf-Dieter Scholz in a sky survey taken by NASA’s WISE observatory. They’re currently about 20 light-years away, and moving away from us at a speed of about 80 kilometers per second.

The interesting thing is that astronomers carefully measured the stars’ sideways motion across the sky, what we call the proper motion, and found it to be very small. That means the stars are heading almost directly away from us … so sometime in the past they must have been much closer!

Eighty kps is pretty fast—2.5 billion kilometers per year, or roughly a light-year every 4,000 years. When you do the math carefully, it turns out these stars passed us just 70,000 years ago!

The exact distance at which they blew by us is harder to tell due to uncertainties in their motion, but the best estimate is that they were about 0.8 light-years away—far closer than the current nearest star, Proxima Centauri, which is 4.2 light-years away. On a galactic scale, that’s really dang close.

Weirdly, though, if you had been standing on Earth, you wouldn’t have seen them. Both stars are intrinsically very faint. The bigger of the two is classified as an M9, barely a star at all. If it were much smaller it wouldn’t have enough mass to fuse hydrogen into helium in its core, the defining characteristic of a star (more or less). The other is an even dinkier brown dwarf, not really big enough to be a star but still far more massive than a planet.

Together, they only manage to shine at a meager magnitude of 18.3—the dimmest star you can see with your naked eye is still over 60,000 times brighter! And even 70,000 years ago when they passed us they still would’ve been too faint to see by naked eye.

flare star
Many low mass stars produce megaflares; this drawing depicts DG Cvn undergoing one, and it's coincidentally a low mass binary as well.

Photo by NASA's Goddard Space Flight Center/S. Wiessinger

Interestingly, the bigger of the two is what we call a flare star: It’s magnetically active, and can have surface eruptions like solar flares, but far more powerful. These explosions can be big enough that briefly, for a few hours or so at a time, the star would’ve been naked eye visible.

I’ll note that it’s not like these two stars whizzed past us like a starship in a movie; even at their velocity they would’ve been relatively close for centuries. I have to wonder if any prehistoric people saw a flare from the star, and wondered where that new point of light in the sky came from … ? But then, they may have had more immediate problems on their minds.

You might think it’s kinda funny we’ve never seen these stars before. They are faint, which makes them more difficult to spot, and they also happen to be in a part of the sky lousy with stars, near the plane of our galaxy. They were hiding in plain sight.

And one final note. Uncertainties in the distance at closest approach means that it’s entirely possible these stars got close enough to very slightly influence our solar system gravitationally; specifically, the Oort Cloud, the huge spherical cloud of giant icy chunks of material orbiting the Sun way, way past Neptune. The gravity of the stars could have disturbed the orbits of these far-flung cometary bodies, dropping them in toward the inner solar system … and us.

But before you panic, note that the time it takes to fall from that distance is about 2 million years! So if we’re going to experience a hail of death from deep space, we have another 1,930,000 years to go. I’m OK with that.

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Feb. 18 2015 7:15 AM

Is Mars Slowly and Surely Drawing Its Plans Against Us … ?

Y’know, I’m not all that big on “Mystery Baffles Scientists!” kinda headlines, but I have to admit, this scientific mystery is rather baffling.

What’s causing hundreds-of-kilometer-high plumes on Mars?

This is pretty weird. Amateur astronomers taking images of the Red Planet spotted cloudlike features well above the surface. And I do mean well; some are 250 kilometers in altitude. That’s way above where you normally find clouds.

They’ve been seen on multiple occasions, and by Hubble as well. They’re not image artifacts or some processing mistake in the pictures. They rotate with the planet, and are certainly real.

[A Mars plume was spotted on Mar. 20, 2012. Photo by W. Jaeschke. Click to embiggen.]

Mars has an atmosphere, though it’s thin, less than 1 percent of Earth’s pressure at sea level. It’s enough to stir up dust storms and other weather on Mars. It even can make clouds: As winds blow up the slopes of the planet’s huge volcanoes, for example, carbon dioxide can condense and form what are called orographic clouds (this happens on Earth too; I see it all the time since I live near the Rocky Mountains, with water instead of carbon dioxide of course).

Still, it’s hard to see how the Martian air could blow something like dust or CO2 as high as these plumes. It’s possible, though unlikely, that it could be some gas in the atmosphere that’s getting up that high, condensing, and forming reflective clouds.

But it’s just so far above what’s normally seen that this doesn’t hold water with me.

Another idea is that it’s auroral activity. Mars doesn’t have much of a magnetic field, but there are areas on the planet that do have stronger magnetic fields. The solar wind coming in from the Sun could be funneled into the atmosphere there, causing the glow. Although the press release doesn’t mention it, I suspect observing Mars in the ultraviolet might help; aurorae glow at those wavelengths.

You’d think that we have plenty of space probes orbiting the planet and that one of them would’ve seen something by now. The problem there is, in a way, being too close. The best way to see these things is on the edge of Mars, against the darkness of space. Most of the orbiting missions at Mars look straight down, and can’t see these plumes.

Not that observing them from Earth is all that easy. The problem is that these aren’t persistent features. They come and go, making observing them difficult. In cases like that, the best bet is brute force: Observe Mars a lot. Get as many telescopes observing it as often as possible and in as many ways as possible (imaging, video, different wavelengths, and so on). Small probability events become certainties given enough time.

I’d love to know what these things are. Giant plumes of gas erupting from Mars sound a little ominous to me. If there’s an observatory in Grover’s Mill, I hope it’s paying close attention.

Feb. 17 2015 11:30 AM

Public Curiosity Talk in Boulder on March 2

Hey, Boulderites! I’ll be giving a talk about Mars and the Curiosity rover at the Chautauqua Community House on March 2, 2015, at 7 p.m. The talk, “Where Has Our Curiosity Taken Us,” is an overview of the mission loaded with cool imagery and fun science.

I’ve given this talk here and there, and I really have fun going over the amazing things we’ve learned since the rover touched down in 2012. I’ll talk about the launch and landing, the roving, the photos, and the science Curiosity has undertaken.

Tickets are $10 ($7 for concert members), and as I write this, about half the seats are already sold. If you want to come, better get a ticket soon! I hope to see some BABloggees there.

Feb. 17 2015 7:15 AM

Why Do Mirrors Reverse Left and Right but Not Up and Down?

I love brain teasers, especially when they’re based on real-world things we see every day but maybe don’t really think about.

I first heard of this one not too long ago: Why do mirrors reverse left and right, but not up and down? When you face yourself in the mirror, left and right are reversed, but you’re still right side up. Why?

The answer may not seem obvious because the question itself frames the problem incorrectly! It makes you try to solve the problem starting from the wrong premise. As it happens, Physics Girl has it covered:

Her use of written words and clothes is pretty clever, but the arrow was really good. That’s what makes it all clear: Mirrors don’t reverse left and right, they reverse in and out. Once you see that it all makes sense.

I really like demos like this; this connects physics to everyday life and also shows that how you frame a problem is in many ways just as important as how you think about a problem.

I met Dianna, aka Physics Girl, last year at Comic-Con; by coincidence I had just seen one of her videos and liked it. You should watch them; she has a knack for explaining things simply and well. I especially recommend the video about vortices in pools; it’s really cool, and these stable swirls of water are really fun to watch. I’ve spent some time in pools (and yes, in the bathtub) creating them and watching them propagate. They seem simple but are surprisingly complex phenomena, especially in how they interact with light.

And why not, here’s the video:

I’d suggest subscribing to her videos, and checking out her website, too. In my opinion, we can’t have enough good people out there communicating fun science. If you know of more, leave a comment below! I’m always looking for that sort of thing.

Feb. 16 2015 12:00 PM

Rosetta Dips Low Over an Alien World

On Saturday, Valentine’s Day, the Rosetta spacecraft dipped down low over the comet 67P/Churyumov-Gerasimenko. How low? At one point, it was less than 9 kilometers from the surface!

Given that the comet is 4.3 kilometers long and shaped like a rubber ducky that’s been sitting in the Sun for 4 billion years, this was a pretty low and gutsy pass. It was done to get extremely high-resolution pictures of the comet, of course, but the spacecraft will also be making a series of more distant passes to sample the environment around the comet at different locations.

Around the time of closest approach, the lower resolution NAVCAM instrument was used to snap photos of the comet. One of them showed the very, very weird Imhotep region of the comet, and, well, see for yourself:

Feb. 16 2015 7:00 AM

Let Me Hold You in My Anomalous Arms

It’s been a while since I have slammed your brain with a huge and gorgeous spiral galaxy, so here’s the brain-slamming gorgeous and huge M106:

Feb. 15 2015 7:30 AM

Pale Blue Dot + 25 Years

Yesterday was the 25th anniversary of the Voyager 1 spacecraft taking one of the most iconic photographs in history: Earth, as seen from more than 6 billion kilometers away.

It was taken under the urging of Carl Sagan, and NASA commanded the spacecraft to rotate so that the camera would take the shot, something that had never been done before from such a distance. As luck would have it, sunlight scattered inside the camera, creating the lovely splashes of light across the frame, one of them, by happenstance, lying across the one tiny, tiny pixel that was all our entire planet could muster.

This image inspired Sagan to write one of the most beautiful and moving passages I’ve ever read, “Reflections on a Mote of Dust,” sometimes called “Pale Blue Dot.”  

The Earth is the only world known, so far, to harbor life. There is nowhere else, at least in the near future, to which our species could migrate. Visit, yes. Settle, not yet. Like it or not, for the moment, the Earth is where we make our stand. It has been said that astronomy is a humbling and character-building experience. There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another and to preserve and cherish the pale blue dot, the only home we've ever known.

That's just an excerpt. Go read the whole thing.

His message was so powerful it has inspired people to create art for it, and even after all these years the words still resonate as strongly as they did in 1990. I have written many times about this essay and the art created in its name. Here a few of those articles; please take a moment to read them, and reflect on what it means to inhabit something so small and remote and wonderful and in such need of our care:

Feb. 14 2015 7:30 AM

Crash Course Astronomy Episode 5: Eclipses

I have friends who tell me that seeing a total solar eclipse is literally life-changing; the serene beauty and majestic clockwork motion of the cosmos unfolding above you is transformative, showing you viscerally the connection between you and other objects in the Universe.

I wouldn’t know. I’ve never seen one.

But that won’t stop me from talking about them! So, just for you, here is 10 minutes of me expositing on eclipses both solar and lunar in Crash Course Astronomy Episode 5:

In the video I mention you can get safe solar viewing glasses online; you can order them from Astronomers Without Borders and from Rainbow Symphony (I have these myself, and I believe that’s what I was wearing in the video). Rainbow Symphony has a wide range of other viewing apparatus as well.

CCA banner
I love that the folks at Thought Cafe, who do our graphics for CCA, drew me with the eclipse glasses on!

And what I said is the truth: I’ve never seen a total solar eclipse for myself. I’ve seen lots of partial ones, but it’s not the same. I think my best chance will be in 2017, when the path of totality crosses the United States, cutting through a lot of places where the weather will almost certainly be good for viewing. It goes through Wyoming, just a few hundred kilometers north of my house, and that may be where I sojourn to see it.

You’ll be hearing a lot more about the 2017 eclipse in the coming couple of years. Make sure you bookmark this Crash Course Astronomy video so you can watch it again when the time comes!

Feb. 13 2015 7:30 AM

Five Years of Staring Into the Sun

Do you have any idea how jaw-droppingly gorgeous our Sun is?

I do. But then I’ve been keeping my eye on NASA’s Solar Dynamics Observatory, which stares at the Sun 24 hours a day, week after week. It sends back very high-resolution images of the Sun in wavelengths from the far ultraviolet—where the Sun’s violent magnetic activity is best seen—through to colors our eyes can detect.

Wednesday was the fifth anniversary of SDO’s launch into space. For the past 1,830 days it has observed our star, and seen a lot of stuff. A lot.

To celebrate, NASA released this sensational video with just a few highlights from this incredible machine. Make sure you’re set to hi-def and turn the volume up because this is sheer amazingness.

There’s so much to take in there. Rolling sunspots, eruptive prominences, collapsing filaments, solar flares, the Transit of Venus (twice!) … if you want more, then just search my blog for “SDO.” I’ve written about it many, many times.

I remember when SDO was still being designed and built, back when I worked at Goddard Space Flight Center. I’d go to lunch with friends, solar astronomers, and we’d talk about what this mission would mean, what it would be capable of. I remember thinking it was crazy how much data it would send back to Earth, and how many different things it would see.

Thinking about those conversations makes me smile now. I had no idea. SDO is far more than I imagined, and has revealed our active and complex star far better than anything before it.

My sincere congratulations to all my friends who work on SDO, to everyone who watches our star and learns what they can about it. We’ve gone around that Sun five times since SDO took to the skies. May we have many more revolutions ahead.

Tip o' the dew shield to Jelle Kouwenhoven.

Feb. 12 2015 7:00 AM

A Seagull Flies on a Dusty Ion Wind

Robert Gendler is an astrophotography whose work I’ve featured here many times (he helped assemblea jaw-dropping Hubble Andromeda galaxy picture, for example). One area in which he excels is taking data from multiple big telescopes and merging them to create new views of the heavens.

His latest is a stunner: the aptly named Seagull Nebula:

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