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Headshot of Jason Davis

The coolest video of an expanding supernova you'll see today

Posted by Jason Davis

09-08-2013 9:32 CDT

Topics: astronomy

When you look at the Crab Nebula, it's hard to fathom you're seeing exploded star remnants zipping outward through space at 3 million miles per hour. After all, you could stare all night at the nebula—located some 6,500 light years from Earth—and fail to notice even a hint of motion.

However, if you wait, say, 13 years, you'll definitely detect some movement. That's exactly what professional astrophotographer Adam Block did, using two images of the Crab Nebula taken more than a decade apart. He created a video that fades back and forth between the two pictures, allowing you to see the nebula expand.

Adam Block

Expansion of M1, the Crab Nebula
The Crab Nebula expands in this animation created with a 1999 image by the Very Large Telescope (VLT) and a 2012 image by the 0.8 meter Schulman Telescope at the Mount Lemmon SkyCenter.

The video has been making the rounds on the Internet, racking up 50,000 views in one week. I've noticed three types of reactions: "Wow!," "I don't get it," and "Why do the colors change?"

I spoke with Adam to help clear up some of the mystery. Let's start with "I don't get it." If you're having trouble seeing the nebula expansion, I find it helpful to focus on a single star as the images blink back and forth. Adam went to great lengths to position the two images so that the stars line up precisely. You can even hover your mouse over a particular strand of gas as a reference point, and watch how it changes between the images. Traveling at 3 million miles per hour, the nebula has expanded by about 315 billion miles over the course of 12 years. For comparison, consider that Voyager 1 has only (only?) traveled 11.6 billion miles since its launch 36 years ago.

The answer to "Why do the colors change?" is a bit more complex. First of all, it doesn't matter; what we're interested in here is the nebula's growth, not its change in color. But let's get an answer anyway.

Adam assures me that the nebula itself did not change color. The color differences are the result of different telescopes and image processing techniques. The 8.2-meter Very Large Telescope—which captured the first image in 1999—was not designed solely to create pretty pictures; it has more important science to do.

M1, the Crab Nebula, by the Very Large Telescope

European Southern Observatory

M1, the Crab Nebula, by the Very Large Telescope
The Crab Nebula, a supernova remnant, was imaged in 1999 by the Very Large Telescope. The resulting picture uses mapped color from three filters.

On the other hand, Adam's telescope, the 0.8-meter Schulman at the Mt. Lemmon SkyCenter, was designed especially for astrophotography. The Skycenter offers nightly public observation programs called SkyNights. When SkyNights wraps up, the Schulman's eyepiece is often swapped out with a CCD camera, allowing Adam and other astronomers to image the Universe. 

M1, the Crab Nebula, by the Mt. Lemmon Skycenter Schulman Telescope

Adam Block / Mount Lemmon SkyCenter / University of Arizona

M1, the Crab Nebula, by the Mt. Lemmon Skycenter Schulman Telescope
The Crab Nebula, as seen by the 0.8-meter Schulman Telescope at the Mt. Lemmon SkyCenter. The SkyCenter is located in the Catalina Mountains just north of Tucson, Ariz.

The VLT image was captured in three narrowband wavelengths: 429 nm (rendered as blue), 657 nm (rendered as green) and 673 nm (rendered as red). If you look at which wavelengths correspond with common colors, you'll see that the VLT rendering choices are somewhat arbitrary. Green, for instance, has a wavelength of about 510 nm; not very close to the 657 nm filter that was used. So while the VLT doesn't offer a true-color representation of M1, it still works for this exercise because the main point is to show how the nebula expands. An alternative would be to use grayscale images, but that wouldn't be as fun. 

Adam's CCD uses broadband filters, which capture the entire range of the visible spectrum. He also used a hydrogen-alpha filter to bring out some of the detail in the filaments, and combined the result into his final image. You can see more of Adam's astrophotoraphy here; most of his images are fairly accurate true-color representations.

Finally, it's worth comparing the time required to capture both images. In the 1999 VLT photo, the exposure times for the three filters are 5 minutes, 1 minute and 5 minutes. That's what happens when you have an 8.2-meter mirror at your disposal. Adam, using a mirror one-tenth that size, had to observe the nebula multiple times over the course of two months, dodging weather constraints and working around the schedules of other research astronomers remotely using the telescope.

So, has your reaction to the video changed? Hopefully, I've managed to get you into the "Wow!" camp.

See other posts from August 2013


Or read more blog entries about: astronomy


Paul Stone: 08/09/2013 11:30 CDT

I'm amazed that no-one has been taking yearly or bi-yearly snapshots of this or similar nebulae using the same wavelengths and exposures. Beyond pretty animations there must be some scientific benefit to studying the way the gas structures evolve over time? Are there any other nebulae that are expanding at similar human-observable speeds?

Michael Richmond: 08/09/2013 11:34 CDT

Actually, other people _have_ been using images of the Crab Nebula taken years apart to demonstrate its expansion. It's pretty common. For example, I've been using this image: for the past eight or nine years in a class I teach. You can read the entire lab exercise at I guess I just never bothered to put out a press release about it.

Stephen Uitti: 08/09/2013 12:31 CDT

Really good images of the Crab go way back. It was one of the first images taken at the 5 meter Polomar, in the 40's. We should be able to cobble together 70 years of expansion.

MrSatyre: 08/09/2013 01:58 CDT

"The answer to "Why do the colors change?" is a bit more complex. First of all, it doesn't matter; what we're interested in here is the nebula's growth, not its change in color. But let's get an answer anyway. Adam assures me that the nebula itself did not change color. The color differences are the result of different telescopes and image processing techniques. The 8.2-meter Very Large Telescope—which captured the first image in 1999—was not designed solely to create pretty pictures; it has more important science to do." What an incredibly stupid series of things to say. As an astronomer, you of all people should know that breaking down the colors of what we're seeing tells us what heavenly bodies can be comprised of. Yes, it DOES matter. Why? Because your readers are, like you, curious about what they're looking at. And, I hate to break it to you, your optical telescopes ARE designed to take pretty pictures. If they can't take pretty pictures, you have nothing to look at. If you want to split hairs and self-righteously talk about "more important science", then you could have mentioned a few as examples without coming across like a d*ck.

Mean & Anomalous: 08/09/2013 02:23 CDT

To MrSatyre - Geez, there are much better ways of saying what you said; your comments gets worse as one reads further. *You* come across as the last word in your post.

Bob Ware: 08/09/2013 04:38 CDT

Great expansion shots! Lots of data in those images. I also like Stephen U.'s idea of "cobbling" together images fro the 40's to current time. Ending with these two would be great! Long but great!

Bob Ware: 08/09/2013 05:03 CDT

Michael R. - I looked a your images and jumped back to these current images. There is a HUGE expansion between the two sets. Take a quick comparison look and you'll see the huge difference.In your last image, look at the bottom left - from the 2 really close together stars, may look like a streak - then jump to the last image in these current sets. If the could be overlaid to each other then it'll be easier to see this HUGE expansion over the few short years. Maybe you two could agree to blend them and show it to the media and maybe they'll run it on some network too. That's reat work you did with your images also!

Mike Martinez: 08/10/2013 02:09 CDT

We become abrasive when we feel threatened---and this is no place to show that weakness. Some valid points were made by some commentators---but please, respond civilly & intelligently. After all, we are dealing with the immense universe which could care less how we find out it's secrets. We become almost irrelevant in our prognostications.

Lindore : 08/10/2013 02:28 CDT

Thank you for this article. I find it very interesting. Can you tell me tho ... . Different telescopes and processing techniques aside ...what true colours would I expect to see if I was able to view the crab with my naked little eye. I love seeing images taken from space they are so beautiful but I would love to see the 'true colours'....... which would not mean I could love them any less of course.

Tom Loman: 08/12/2013 10:02 CDT

The parts of the nebula that are blue are moving away from the observer, the parts of the nebula in red are moving toward the observer. The white parts of the nebula are remaining roughly the same distance from the observer.The wavelength of blue light is longer than that of red light, so as the light source moves away from us, it takes longer for the light to reach us, resulting in a blue hue. Likewise, as it moves closer, the waves are compressed resulting in a red appearance. This is known as the blue-shift theory.

Jason Davis: 08/12/2013 05:27 CDT

Tough crowd, but I'm glad to see that this post has created a lively discussion. I should do more astronomy stories. Here are a couple responses to your comments: Michael Richmond: Actually, Adam says the animation you are using in your lab is also one he created. If that's the case, you can now update it with this new version :) MrSatyre: We'll have to agree to disagree. 1) I'm not an astronomer. 2) I didn't say colors don't matter in astronomy. I said that for this particular exercise, in which we are watching the nebula expand, the difference in color between the two images doesn't matter. 3) Saying the VLT has more important science to do than solely creating pretty pictures isn't self-righteous talk; it's fact. A lot of astronomy research does not produce pretty pictures, and proposing to use a large research telescope solely for the purpose of showing something pretty to the public isn't going to get you observing time. Lindore: Adam's photograph is close to true-color. As I said in the article, the VLT image was constructed using narrowband filters, whereas Adam uses broadband filters, which capture a much wider portion of the visible spectrum. Tom: Actually, the gas is moving too slowly for any discernable redshift/blueshift. Three million mph is still only 0.004 times the speed of light. Adam tells me that in this case, the reds and blues are actually caused by varying degrees of energized gas within the supernova remnant. The outer edge glows as it collides with interstellar space. Everything else is glowing due to temperature, or radiation absorption/emission/reemission. The center glows due to strong magnetic fields, which cause synchrotron radiation.

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