Comments on: Crabby Hubble

By: Rural Rambles: Larry Ayers’ Weblog » Tangled Bank # 43

Rural Rambles: Larry Ayers’ Weblog » Tangled Bank # 43 — Wed, 14 Dec 2005 16:59:54 +0000

[...] Crabby Hubble [...]

By: Pittsburghmuggle

Pittsburghmuggle — Sun, 11 Dec 2005 19:30:47 +0000

I like the double star in the lower left corner of both animations – you can see the smaller star moving!

By: Jon Niehof

Jon Niehof — Fri, 09 Dec 2005 19:26:17 +0000

Irishman–good question! In fact, there have been times when composition and doppler were confused, resulted in the supposed “discovery” of substances like “nebulum.” We know it’s a Doppler shift because the line spacing is quite unique and there are a *lot* of them. If every single one of dozens of lines is shifted by an amount that indicates the same velocity, and dozens of lines of some element are shifted by an amount that *also* indicates the same velocity, Occam’s Razor (as well as general probability) suggests that it’s more likely a doppler-shifted spectrum of elements we already know, rather than some exotic material that *just happens* to be like that.

By: JusANuttaBackYahdah

JusANuttaBackYahdah — Fri, 09 Dec 2005 02:05:29 +0000

Telescopes are a time machine, moonflake, but did you know they work in both directions? I’m just returning from a small star party I held for a local kids group. I always enjoy showing something like the Andromeda galaxy; telling the folks that the light took 2.5 million years to reach us which is always followed by a WHOA!!! It’s funny though, I always see the future when I get a kid to react like that
One WHOA-fact about the Crab not mentioned is that various records of the sky event that created this nebula show that the supernova was naked eye visible in daytime skies for some twenty-odd days. Now that’s a WHOA!
Clear skies

By: Irishman

Irishman — Thu, 08 Dec 2005 16:44:41 +0000

Here’s what bugs me about the Doppler shift in spectra – how is it that we conclude that the spacing of gaps and lines is shifted and not from a different combination of elements? For instance, I saw a TV show discussing this. The show came up with a reenactment of some 19th century astronomer making discoveries, and showed him and his lab assistant operating the telescope, showed him taking the image and then going to develop it. They spent five minutes on this silly reenactment, and then squeezed in one example of comparing the spectra to show the shift. To me it would have been much more informative to skip the silly acting and show a dozen spectral comparisons and demonstrate how the comparisons are made and why scientists interpret the changed patterns as shifts rather than just different combinations.

By: moonflake

moonflake — Thu, 08 Dec 2005 12:38:42 +0000

The idea that when we look up at the sky we look back in time, to the universe as it was thousands or millions or billions of years ago… we already have built time machines, they’re called ‘telescopes’. Love it.

By: Marlayna

Marlayna — Thu, 08 Dec 2005 10:31:41 +0000

Thanks, I think I got it

By: Andy

Andy — Wed, 07 Dec 2005 23:38:40 +0000

also, couldn’t you measure how far it’s gone from where the star used to be, since we know when the nova occured? it’d be extremely rough, but that should be good enough for back of the envelope calculations. you could probably even do with just a picture that had a scale on it, but you’d have to make sure you meausured the gas farthest from the star, where it’s path is perpendicular to your line of sight.

By: Evolving Squid

Evolving Squid — Wed, 07 Dec 2005 22:21:15 +0000

The speed of the gas would produce a doppler shift in its spectrum, the same way a car racing by you seems to raise in pitch as it approaches and lower in pitch as it passes.

One can measure the doppler shift, and from that calculate the speed of moving stuff.

By: Irishman

Irishman — Wed, 07 Dec 2005 21:58:44 +0000

I think Marlayna’s question may have more to do with how to calculate the speed from the spectrum.

By: The Bad Astronomer

The Bad Astronomer — Wed, 07 Dec 2005 21:53:13 +0000

Marlayna– when you compare the two pictures, you are only measuring the gas speed in terms of degrees/year or something like that. The spectrum gives you the speed in km/sec. Those can then be combined to get a size of the nebula and its distance. If a blob is moving at, say 500 km/sec, and you know how far it traveled in a given amount of time, you get a size of the nebula. Once you know the size of the nebula in km, you can measure its apparent size and get the distance to it.

By: Marlayna

Marlayna — Wed, 07 Dec 2005 20:32:21 +0000

I read on one of those links that they calculate the speed of the gas based on the spectrum of the light it gives off.

Now I’m confused. What does that have to do with anything?

By: Evolving Squid

Evolving Squid — Wed, 07 Dec 2005 18:54:09 +0000

>1400 km/s

The speed of light is approximately 300 Mm/s. Despite that speed, it still takes 214 years to travese a light year.

This would seem to indicate that in about 1.4 million years, the nebula bits will pass our solar system. Better get a net and put on some coffee

On a more serious note, though, it also implies that planetary nebulae have a relatively limited life-span. Presumably the Crab nebula will dissipate, from our point of view, long before 1.4 million years. Is there any research/thoughts about how long planetary nebulae last?

By: arensb

arensb — Wed, 07 Dec 2005 17:59:20 +0000

more energy than the Sun puts out in millions of years

Okay, now my brain hurts. Humans just aren’t built to grok anything that large.

By: Chip

Chip — Wed, 07 Dec 2005 17:22:52 +0000

Animations spanning 28 years are cool, but has anyone every gone back to the earliest photographed images of the Crab Nebula (1890s?) and carefully put together images collected from every year of observation? A 100+ years of smoothly expanding gases, though still a short animation from that distance, would be interesting.

By: Rodolfo Granados

Rodolfo Granados — Wed, 07 Dec 2005 16:07:22 +0000

Andy

The space shuttle does NOT travel at 7600 Km/sec. At that speed it would complete an orbit in less than 6 seconds! Its speed is around 7.7 Km/sec

Absolutely stunning image of the Crab Nebula!

By: Jon Niehof

Jon Niehof — Wed, 07 Dec 2005 14:39:52 +0000

That before/after image is neat, except what I presume is the after (more expanded) image pretty clearly has a different exposure time or filter–the dimmer stars appear brighter in it. So the dimmer nebulosity would also appear brighter and make the nebular appear to expand, which unfortunately confuses the issue.

By: antipodean

antipodean — Wed, 07 Dec 2005 13:16:37 +0000

oops, my bad, i misread the book, it actually says Edmund Halley, sorry about any confusion

By: antipodean

antipodean — Wed, 07 Dec 2005 12:35:30 +0000

hey, thats my background

on another note about hubble, i found this in a DK guide to the universe, and i quote:
“The French comet hunter Charles Messier (1730-1817) compiled a catalogue of 110 nebulous-looking objects in the sky that could be mistaken for comets. Not all were discovered by himself – many were spotted by another Frenchman, Pierre Mechain, and yet others had been found YEARS EARLIER BY ASTRONOMERS SUCH AS EDWIN HUBBLE.”

I’m pretty sure Hubble was born a good 40+ years after Messier died, so how is this possible? You’d think when writing a science book they’d at least check their facts.

By: Blake Stacey

Blake Stacey — Wed, 07 Dec 2005 09:47:40 +0000

The actual explosion happened 6,500 years before we Earthers saw it, but today, we see it as it was 6,500 years ago. We still see the nebula as it was when it was about a thousand years old.

To the best of my knowledge, the exact date (4 July 1054) comes from the date the Chinese astronomers recorded a “guest star” appearing in the sky. Not being an expert in calendrical conversions, I don’t know how tough it is to change a Chinese date into a Gregorian one. Given the whole Gregorian/Julian mess and a Chinese calendar about as complicated as the Hebrew one, conversion-wise, I’d expect a probable error of a day or two in either direction. (It’s like figuring out on what day Passover fell, 950 years ago.) I read this in L. A. Marschall’s **The Supernova Story** (1988), but I don’t have the book with me to check the details.

By: moonflake

moonflake — Wed, 07 Dec 2005 09:27:15 +0000

Surely the calculated date of the explosion is not actually the date of the explosion, only the date at which the light from the explosion reached us? The actual explosion would have happened 6,500 years earlier than that. Or am I confused?

By: Andy

Andy — Wed, 07 Dec 2005 07:40:25 +0000

oh, KM/s.

doh. nevermind

By: Andy

Andy — Wed, 07 Dec 2005 07:39:58 +0000

1400km/s ?

the space shuttle goes at 7600+ km/s

or is that a typo?

By: asgromo

asgromo — Wed, 07 Dec 2005 07:04:09 +0000

I love this stuff too. =D It’s the really practical elements of astronomy (one might say the really superficial ones) that affect me the strongest.

By: Eric Ingram

Eric Ingram — Wed, 07 Dec 2005 06:52:28 +0000

Whoa, the old/new images animation just blew my mind. Ouch.