# A question about Novas, Pulsars and other obscure celestial phenomenon. **URL:** \ **Category:** Factual Questions\ **Created:** [January 13, 2008, 10:14pm UTC](https://boards.straightdope.com/t/a-question-about-novas-pulsars-and-other-obscure-celestial-phenomenon/433412 "2008-01-13T22:14:33Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![Phlosphr](https://avatars.discourse-cdn.com/v4/letter/p/c68b51/32.png) [@Phlosphr](https://boards.straightdope.com/u/Phlosphr)\ **Post date:** [January 13, 2008, 10:14pm UTC](https://boards.straightdope.com/t/a-question-about-novas-pulsars-and-other-obscure-celestial-phenomenon/433412/1 "2008-01-13T22:14:33Z")
I have a question about [those](http://uk.gizmodo.com/hubble.jpg) [beautiful](http://chandra.harvard.edu/photo/2006/crab/crab_hubble.jpg) [images](http://www.klab.caltech.edu/~ma/Hubble.jpg) taken by Hubble and other telescopes…Particularly the images of nova, pulsars and other seemingly dyamic phenomena. What’s going on the instant they are taking the picture? How fast is the image moving when the picture is taken? Is it quickly, so the image would be something completely different the instant after the shot? Or is it moving incredibly slowly? I know they are altered to add coloring and an artists renditon of the event…but just how dynamic is the event happening the instant it is being photographed? ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [January 13, 2008, 10:27pm UTC](https://boards.straightdope.com/t/a-question-about-novas-pulsars-and-other-obscure-celestial-phenomenon/433412/2 "2008-01-13T22:27:34Z")
Pulsars can cycle between minimum and maximum brightness within spans of hundredths of a second to several minutes or more. They tend to slow as they age. Supernovae typically blossom to full brightness over a period of several hours to a few days. Although this seems slow, the expanding gases and other ejecta can attain speeds of up to around 3% of the speed of light (about 5,500 miles per second), which is arguably pretty damn fast. ---
**Author:** ![Phlosphr](https://avatars.discourse-cdn.com/v4/letter/p/c68b51/32.png) [@Phlosphr](https://boards.straightdope.com/u/Phlosphr)\ **Post date:** [January 13, 2008, 10:33pm UTC](https://boards.straightdope.com/t/a-question-about-novas-pulsars-and-other-obscure-celestial-phenomenon/433412/3 "2008-01-13T22:33:57Z")
[QUOTE=Q.E.D.] Pulsars can cycle between minimum and maximum brightness within spans of hundredths of a second to several minutes or more. They tend to slow as they age. Supernovae typically blossom to full brightness over a period of several hours to a few days. Although this seems slow, the expanding gases and other ejecta can attain speeds of up to around 3% of the speed of light (about 5,500 miles per second), which is arguably pretty damn fast. [/QUOTE] I knew they were moving fast! When we see them in photos people oohh and ahh about them but they are not as static as the photo makes them look, I think that is really fascinating to think about. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [January 13, 2008, 10:56pm UTC](https://boards.straightdope.com/t/a-question-about-novas-pulsars-and-other-obscure-celestial-phenomenon/433412/4 "2008-01-13T22:56:06Z")
OK, first I think that [those](http://uk.gizmodo.com/hubble.jpg) is an artists rendering, not an actual photo. Second, while pulsars can vary quickly in brightness, what makes the second and third pictures interesting is the gasses, and those are, what, lightyears? across. They are not going to be varying appearance quickly. If a second picture was taken now, the differences would be slight. ETA: The Crab Nebula (the second image) is from a supernova from 1050, almost 1000 years ago. There won’t be a lot of change in its image over a year or two. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [January 13, 2008, 11:04pm UTC](https://boards.straightdope.com/t/a-question-about-novas-pulsars-and-other-obscure-celestial-phenomenon/433412/5 "2008-01-13T23:04:08Z")
[QUOTE=ZenBeam] OK, first I think that [those](http://uk.gizmodo.com/hubble.jpg) is an artists rendering, not an actual photo. [/QUOTE] No, [those](http://heritage.stsci.edu/2003/28/index.html) is an actual Hubble image of the so-called Sombrero Galaxy. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [January 13, 2008, 11:23pm UTC](https://boards.straightdope.com/t/a-question-about-novas-pulsars-and-other-obscure-celestial-phenomenon/433412/6 "2008-01-13T23:23:49Z")
[QUOTE=ZenBeam] what makes the second and third pictures interesting is the gasses, and those are, what, lightyears? across. They are not going to be varying appearance quickly. If a second picture was taken now, the differences would be slight. [/QUOTE] Like this: Changes in the inner Crab Nebula over a four month period. More about the picture [here](http://seds.org/MESSIER/more/m001_h2.html). ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [January 14, 2008, 2:20am UTC](https://boards.straightdope.com/t/a-question-about-novas-pulsars-and-other-obscure-celestial-phenomenon/433412/7 "2008-01-14T02:20:14Z")
> [@](#): > > No, those is an actual Hubble image of the so-called Sombrero Galaxy. I stand corrected. It looked too perfect to be an actual photo. > [@](#): > > Like this: Changes in the inner Crab Nebula over a four month period. I suspect you/re disagreeing with me too, but I’m not seeing it in the pictures you linked to. Also, I don’t know how long apart they were taken, but comparing the [Palomar picture](http://seds.org/MESSIER/Pics/Jpg/m1h_a.jpg) from the top, left of [your link](http://seds.org/MESSIER/more/m001_h2.html) to [**Phlosphr** ,s link from the Hubble](http://chandra.harvard.edu/photo/2006/crab/crab_hubble.jpg), the biggest difference seems to be the resolution. (OK, we really need to rotate and resize one of the pictures to compare them accurately, but I don’t have time right now.) ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [January 14, 2008, 2:36am UTC](https://boards.straightdope.com/t/a-question-about-novas-pulsars-and-other-obscure-celestial-phenomenon/433412/8 "2008-01-14T02:36:01Z")
[QUOTE=ZenBeam] I suspect you/re disagreeing with me too [/QUOTE] Not really, just showing that there can be visible changes in nebula over a matter of months. Perhaps a better example would be [this movie](http://apod.nasa.gov/apod/ap030402.html) of [V838 Monoceros](http://apod.nasa.gov/apod/ap030402.html), which shows light traversing a nebula over the course of eight months. [Hubble’s variable nebula](http://apod.nasa.gov/apod/ap991020.html), [Hind’s Variable Nebula](http://www.daviddarling.info/encyclopedia/H/Hinds_Variable_Nebula.html), and [McNeil’s Nebula](http://apod.nasa.gov/apod/ap040219.html) also change visibly over the course of weeks to months. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [January 14, 2008, 8:09pm UTC](https://boards.straightdope.com/t/a-question-about-novas-pulsars-and-other-obscure-celestial-phenomenon/433412/9 "2008-01-14T20:09:13Z")
[QUOTE=ZenBeam] I suspect you/re disagreeing with me too, but I’m not seeing it in the pictures you linked to. [/QUOTE] You mean you don’t see any change in this picture? Look at the lower half of the image, below and to the right of the “eye”. There’s quite a bit of change in the gas cloud structure. Though of course, most deep-sky objects change very little over time. Notable exceptions are pulsars (as already mentioned), and variable stars which can change brightness in a matter of days or sometimes hours. Novas and supernovas brighten very fast at the onset too. But if you want truly dynamic astrophysical phenomena, take a look at features on the sun, e.g. those observed by[TRACE](http://trace.lmsal.com/POD/TRACEpod.html). ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [January 14, 2008, 8:29pm UTC](https://boards.straightdope.com/t/a-question-about-novas-pulsars-and-other-obscure-celestial-phenomenon/433412/10 "2008-01-14T20:29:33Z")
[QUOTE=scr4] if you want truly dynamic astrophysical phenomena, take a look at features on the sun, e.g. those observed by[TRACE](http://trace.lmsal.com/POD/TRACEpod.html). [/QUOTE] This movie documenting [changes in the X-ray sky over a 10 year period](http://www.space.com/scienceastronomy/060118_xray_movie.html) is also not chopped liver. ---
**Author:** ![Angua](https://avatars.discourse-cdn.com/v4/letter/a/8baadc/32.png) [@Angua](https://boards.straightdope.com/u/Angua)\ **Post date:** [January 14, 2008, 8:49pm UTC](https://boards.straightdope.com/t/a-question-about-novas-pulsars-and-other-obscure-celestial-phenomenon/433412/11 "2008-01-14T20:49:03Z")
[QUOTE=ZenBeam] OK, first I think that [those](http://uk.gizmodo.com/hubble.jpg) is an artists rendering, not an actual photo. Second, while pulsars can vary quickly in brightness, what makes the second and third pictures interesting is the gasses, and those are, what, lightyears? across. They are not going to be varying appearance quickly. [/QUOTE] As an astrophysicist, the differences are sufficient that data taken a couple of years, and in some cases months or even days apart can indeed tell us a great deal about velocities, rates that phenomena are occuring at, expansion speeds of the gas etc, all of which add up to inform us about the physics. And just because you can’t see a visible change from a cursory glance at a false-colour image, doesn’t imply that there aren’t changes happening on a spectral and timing level. Telescopes like _Chandra_ and indeed _Hubble_, don’t just have the capability to detect photons hitting the sensors, they can detect energies (to a very high resolution), and make timing measurements too. And in many cases, a spectrum, i.e. a histogram of counts/second versus energy or a light curve (total counts as a function of time), can tell us so much more than a simple image can. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [January 14, 2008, 9:30pm UTC](https://boards.straightdope.com/t/a-question-about-novas-pulsars-and-other-obscure-celestial-phenomenon/433412/12 "2008-01-14T21:30:25Z")
The pictures you see taken with Hubble are prettier than what you would see if you could look through Hubble with an eyepiece because they have a very long exposure time to detect things too faint to be seen by eye, and also sometimes because their color has been made more intense or remapped from other spectral ranges. Making the colors more saturated (more intense hue) has better technical justification than you might think - the apparent saturation of colors falls off faster than the apparent brightness because of nonlinear behavior in the eye, so there isn’t just one version of what the “natural color” should be. Remapping colors from other spectral regions is the only way to see some things at all, because we just don’t see the interesting wavelengths in these cases. Other than turning the saturation up and perhaps remapping color, I don’t think they doctor Hubble pictures much. Practically all the beautiful images from Hubble and other big observatories are static in the sense that if you were seeing it through an eyepiece, perhaps with some magical means to amplify the brightness and intensify the colors, you wouldn’t see anything moving. There are a few weak exceptions. Meteors move fast and vanish quickly, and they are arguably at the edge of space, but nobody can aim a telescope at one fast enough to view them that way. Objects slamming into the Moon or Mars or Jupiter create brief flickers of light, but these are very rare events from the point of view of the skywatcher with a telescope. There are pulsars that flash on and off at rates that would be visible, and pulsars sometimes turn on and off in visible light, but I’ve never heard of any you can watch blinking. Maybe there aren’t any bright enough. You can see the Moon moving when it covers and uncovers stars (“lunar occultations”), and some people have expressed pretty giddy sensations of the clockwork of the universe after seeing this, though there aren’t as many occultations of nice bright stars as we’d like. Generally, though, what you see through a telescope only moves because it’s hard to make telescope mounts as stiff as we wish. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [January 15, 2008, 3:35am UTC](https://boards.straightdope.com/t/a-question-about-novas-pulsars-and-other-obscure-celestial-phenomenon/433412/13 "2008-01-15T03:35:37Z")
> [@](#): > > You mean you don’t see any change in this picture? Look at the lower half of the image, below and to the right of the “eye”. There’s quite a bit of change in the gas cloud structure. Yes, but that’s not at all like the pictures **Phlosphr** linked to. For **Phlosphr** ’s images, what you’re seeing that makes them interesting is the dust and gasses, which, while certainly moving, are moving so slowly in terms of pixels of the image, that the answer to the OP’s question “Is it quickly, so the image would be something completely different the instant after the shot?” is “No.” > [@](#): > > And just because you can’t see a visible change from a cursory glance at a false-colour image, doesn’t imply that there aren’t changes happening on a spectral and timing level. Yes, but again, my interpretation of what the OP is asking (and maybe **Phlosphr** can clarify) is whether the structures that you see just by looking at the picture are changing noticeably from hour to hour or even day to day. I can confirm that the Hubble and the Palomar pictures of the Crab Nebula have essentially the same filamentary structure, although I have no idea how long apart the pictures were taken. But if it’s changing even month to month, there ought to be lot’s of noticeably different pictures _similar to the one the OP liked to_ that someone could provide links to. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [January 15, 2008, 4:16am UTC](https://boards.straightdope.com/t/a-question-about-novas-pulsars-and-other-obscure-celestial-phenomenon/433412/14 "2008-01-15T04:16:08Z")
[QUOTE=ZenBeam] But if it’s changing even month to month, there ought to be lot’s of noticeably different pictures _similar to the one the OP liked to_ that someone could provide links to. [/QUOTE] Here’s a famous [picture of changes in the crab nebula over 14 years](http://www.pas.rochester.edu/~afrank/A105/LectureXII/FG21_010_PCT.jpg). The caption [from here](http://www.pas.rochester.edu/~afrank/A105/LectureXII/LectureXII.html) reads: > [@](#): > > Difference Image Showing Expansion Of The Crab Nebula - Positive and negative photographs of the Crab Nebula taken 14 years apart do not superimpose exactly, indicating that the gaseous filaments are still moving away from the site of the explosion.