NGC 3621: Far Beyond the Local Group (2009 September 19)

[orin stepanek]

http://apod.nasa.gov/apod/ap090919.html

. Some of its brighter stars have been used as standard candles to establish important estimates of extragalactic distances

Just how do standard candles work? I mean; It's still just educated guess work, isn't it? All in all it is a beautiful picture, though most galaxies are. 8)
I found this but it is still a bit confusing.
http://en.wikipedia.org/wiki/Cosmic_distance_ladder

Orin

[CuDubh]

Say what? 22 million light years is not "far beyond" the local group.
Only ten times as distant as M31.
By comparison, if the Milky Way-Andromeda distance were scaled down to the radius of the earth's orbit about the sun, NGC3621 would lie halfway between Jupiter and Saturn.

[Craine]

The image contains a number of defects or optical effects of some kind. Mostly they seem to be several grouping of black dots spread out at seemingly random places. And in one case, above and to the right of NGC 3621, 6 white dots circling a 7th dot. Does anybody have an idea how these are caused? Or did we find the Fleet of Worlds?

[ketarax]

Does anybody have an idea how these are caused? Or did we find the Fleet of Worlds?

I suppose they were caused by a pencil There's also a pattern for 5, and the one for 7 appears in
several places.

[Chris Peterson]

Just how do standard candles work? I mean; It's still just educated guess work, isn't it?

I suppose you could say that every conclusion drawn from an observation is an "educated guess". But that's probably not the term I'd use.

A standard candle is a light source (normally a star) with a known brightness. If you know the brightness, you can estimate the distance. Certainly there are assumptions involved: that the object is actually what we think it is, that the rules of physics are the same at its location as they are nearby, that nothing in the intervening space is absorbing light. Every observation comes with assumptions, though; this is no different. The assumptions seem reasonable, and standard candle measurements are consistent with each other (and with other measurements obtained by different methods, as outlined in your distance ladder reference), so there is a high level of confidence that the assumptions are valid.

[orin stepanek]

Thanks Chris; that's a pretty good reply. I'm not familiar with the math; but I accept the the procedure. I do; however, find it quite amazing what man has achieved. I know solar system distances have to be pretty accurate or we wouldn't be able to go to Pluto with a probe; which is quite an achievement also.

Orin

[neufer]

Just how do standard candles work? I mean; It's still just educated guess work, isn't it?

I suppose you could say that every conclusion drawn from an observation is an "educated guess". But that's probably not the term I'd use.

A standard candle is a light source (normally a star) with a known brightness. If you know the brightness, you can estimate the distance. Certainly there are assumptions involved: that the object is actually what we think it is, that the rules of physics are the same at its location as they are nearby, that nothing in the intervening space is absorbing light.

• -----------------------------------------------
  . The Merchant of Venice > Act V, scene I
  
  PORTIA: How far that little candle throws his beams!
  . So shines a good deed in a naughty world.
  
  NERISSA: When the moon shone, we did not see the candle.
  
  PORTIA: So doth the greater glory dim the less:
  -----------------------------------------------
  . Macbeth > Act V, scene V
  
  MACBETH: And all our yesterdays have lighted fools
  . The way to dusty death. Out, out, brief candle!
  -----------------------------------------------
  . King Lear > Act I, scene IV
  
  Fool: So, out went the candle, and we were left darkling.
  -----------------------------------------------

[Gecko23]

The image contains a number of defects or optical effects of some kind. Mostly they seem to be several grouping of black dots spread out at seemingly random places. And in one case, above and to the right of NGC 3621, 6 white dots circling a 7th dot. Does anybody have an idea how these are caused? Or did we find the Fleet of Worlds?

I came here to post what I think is the same thing. Here's an example, cropped from today's APOD. Why does this appear in this image? I'm sure there is a good reason, but I am curious, and I want to learn that reason.

[neufer]

The image contains a number of defects or optical effects of some kind. Mostly they seem to be several grouping of black dots spread out at seemingly random places. And in one case, above and to the right of NGC 3621, 6 white dots circling a 7th dot. Does anybody have an idea how these are caused? Or did we find the Fleet of Worlds?

I came here to post what I think is the same thing. Here's an example, cropped from today's APOD. Why does this appear in this image? I'm sure there is a good reason, but I am curious, and I want to learn that reason.

It's navigation lights on Darth Vader`s Tie X1 Fighter:

<<In the battle of Yavin Darth Vader takes a ship into combat against the Rebels himself. This prototype ship, the TIE Advanced X1, features an original rear-deck spaceframe and reinforced durasteel-alloy hull built around standard TIE/In cockpit and wing brace elements. While similar to the standard TIE/In in many components, the advanced X1 sports a more powerful drive system. Speed performance is only slightly better than the TIE/In, however, due to the added mass of the vessel, which includes hyperdrive and shields. A good deal of the ship's extra power is bled off to the shield generators. While less maneuverable than standard TIE fighters, it can take a beating. The TIE Advanced X1 has twin heavy-blaster cannons in a fixed, front-mounted position, like the TIE/In. In addition to its shields, it had a modest hyperdrive but no life support system. Against the Rebel X-wing and Y-wing fighters in the Death Star trench, Darth Vader's personal ship proves to be a devastating opponent, and Vader cuts down one pilot after another with the X1's high technology.>>

[Chris Peterson]

I came here to post what I think is the same thing. Here's an example, cropped from today's APOD. Why does this appear in this image? I'm sure there is a good reason, but I am curious, and I want to learn that reason.

Well, the pattern is present in a few places in the image. It could be a processing artifact, but my guess would be some sort of watermarking technique. Rob Gendler does sell his images...

[Freefall74]

Anyone notice this (I had to look at the full size picture to see it.
There are seven dots on the image that look a little too symmetrical.
Is this an illusion/aberration/camera trick?
I've circled the region here:
http://www.geocities.com/shadow1122/ngc ... fall74.jpg

[bystander]

Anyone notice this (I had to look at the full size picture to see it.
There are seven dots on the image that look a little too symmetrical.
Is this an illusion/aberration/camera trick?
I've circled the region here:
http://www.geocities.com/shadow1122/ngc ... fall74.jpg

See: Gecko23: Re: NGC 3621 - Image defects or Fleet of Worlds?

[Freefall74]

How the heck did I miss those posts above? I must not have seen the images while at work. Damned websense.

[BMAONE23]

Must be that "Long ago in a galaxy far far away" place

[Craine]

I am kinda dissapointed that nobody commented on my Larry Niven reference.