Honesty in Observing:
The Crab Nebula & an 8.2-m telescope

Posted By Pamela on Mar 13, 2007 | 3 comments

The Crab Nebula as seen by SubaruAs I’ve mentioned before, press releases that don’t really contain science are one of my pet peeves. That said, one such press release came across my inbox this morning and made me giggle happily. The image was of the Crab Nebula (above left: credit: NAOJ); a nearby supernova remnant formed in 1054. The telescope in question was Subaru; an 8.2-m telescope in Hawaii operated by Japan’s National Institutes of Natural Science. Subaru isn’t a facility that buries reporters in press releases. This pretty picture was just press release #4 for 2007, and the other three were solid new results (as were all the non-instrument or education related releases of 2006). So why did this non-science press release from such a respectable press office make me giggle?

Here is a quote from Toru Yamada, one of the observing team’s members: “We just wanted to look at something beautiful.”

I love honestly.

Every astronomer has dreamed of doing this (and many of us have). You are at the scope – some multi-meter behemoth capable of peering into the ultimate galactic hearts of darkness – and you just want to take a picture of some pretty binocular object. Ethics generally requires that we don’t. Our time is allocated based on how much time we need to observe set objects to obtain specific scientific goals. When we are at the telescope controls, we had best be chasing science if we ever want to get telescope time ever again. There is wiggle room in this. If I’ve proposed to observe galaxy clusters A, B, and C, and I realize the also observable cluster E fits my science goals better, on many scopes it’s okay if I add in E and maybe drop C. But, if I’m supposed to be studying the evolution of galaxy clusters, I probably shouldn’t be pointed at my favorite nebula all night.

The “generally requires” and “probably shouldn’t” in the above paragraph are there because there are certain times when I can point the telescope anywhere that I can safely observe without concern for the science I’m obtaining. Those times include mediocre weather (which prevents me from doing my science) and the fragments of the night when it’s dark enough to see a bright binocular object but not dark enough to see my beloved very faint objects (thus preventing me from doing my science).

The image of the Crab Nebula in the Subaru Press Release was taken in one of these stolen moments when some observations are possible, just not the desired observations of science targets. The press release doesn’t state what was wrong, but the normal culprits are clouds sitting only on top of the target object(s), winds coming out of the direction of the target object (at certain wind speeds, it isn’t safe to point the dome into the wind because the dome opening acts like a sail and tears the dome off its tack), or high cirrus is present blocking just enough photons to make faint object imaging impossible. While these three problems can destroy a science program (and make a grad student trying to finish a dissertation project cry), they do allow observers the freedom to take pretty pictures or target pet objects.

These images we steal with our multi-million (or even billion) dollar telescopes aren’t wasted photons. These images are often used for educational work, or to add data points to projects. For instance, according to Toru Yamanda, “My foreign colleagues are interested in the data, which could be useful for research into how the Crab Nebula expands over time.” If you look at a series of images taken over years, you can see the nebula slowly expanding, its tendrils of gas seemingly reaching out and engulfing more and more stars across the decades. As the Crab’s arms collide with material they may change shape and speed. With each new year’s images, we have a chance to see new changes in expansion rate and shape – Subaru’s image can be used to look for these changes. My own stolen moments at the telescope control console have been used to get pictures of large galaxies, star clusters and nebula that I now use to teach CCD data reduction and analysis to students.

But, at the end of the night, we all have to admit, we each like the occasional (and we really do hope they are occasional and brief!) moment we have to just look at something breathtakingly beautiful. Astronomy isn’t all about pretty pictures. The science images I need of star fields are in fact remarkably boring. But… While I am captivated by Astronomy’s deep intellectual mysteries, it was Astronomy s beauty the first seduced me, and that beaty still calls to me.


  1. Hi. Where did we come from and how fast are we traveling? I am refering to the actual direction distance and speed.

    Presumably with the earth moving away from the point of the “big bang,” how would you describe in precise terms the location our planet was at, say 6 months ago relative to where we are today, or relative to where the actual “Big Bang” occured?

    How would one describe the directional placement of a worm hole if you wished to travel in time, given a starting point of here and now, and a desire to reach a past temporal location?

    Have I been reading too much Si Fi? Sorry but it’s always been a question that bothered me.

    I relly enjoy the Astronomy Cast. Thanks!

    Craig Walker

    PS…Dr. Pam has the most sensuous voice I have ever heard.

  2. Hi Craig,

    One of the odd things about our universe is that every point is the center of the universe. . Everything was at one time at that single point of beginning, and everything expanded apart, but the expansion wasn’t from anyone one point. Think of it this way, if you put a rubberband around your fingers while they are closed and then stretch the rubberband by extending your fingers into an O, form what point on the rubber band did the rubberband expand? The whole rubber band expanded, each point pulling away from every other point. Its weird to say, but every point was the center of the universe, which means each of us occupies a place that was the center of the universe.

    As for worm holes… that starts to get into untestable areas of neat sci fi and ugly untestable math.

    Thanks for listening to Astronomy Cast!


  3. Do you think crab nebula can destroy a planet because i read about it and it occupy the titan moon they said the surface of the titan moon expand hmmmmmmmmm what do you think im just 15 yrs old curious about this thing

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