APOD: The Milky Way Over the Arizona... (2015 Feb 23)

[APOD Robot]

The Milky Way Over the Arizona Toadstools

Explanation: Which is older -- the rocks you see on the ground or the light you see from the sky? Usually it's the rocks that are older, with their origin sentiments deposited well before light left any of the stars or nebulas you see in the sky. However, if you can see, through a telescope, a distant galaxy far across the universe -- further than Andromeda or spiral galaxy NGC 7331 (inset) -- then you are seeing light even more ancient. Featured here, the central disk of our Milky Way Galaxy arches over Toadstool hoodoos rock formations in northern Arizona, USA. The unusual Toadstool rock caps are relatively hard sandstone that wind has eroded more slowly than the softer sandstone underneath. The green bands are airglow, light emitted by the stimulated air in Earth's atmosphere. On the lower right is a time-lapse camera set up to capture the sky rotating behind the picturesque foreground scene.

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[geckzilla]

Today's APOD is a wonderful blend of geology and astronomy. I hadn't thought about comparing the age of the star light and the age of rocks before.

[ShaileshS]

Hi, I'm a bit confused by this statement in the explanation - "Usually it’s the rocks that are older, with their origin sentiments deposited well before light left any of the stars or nebulas you see in the sky". I thought the stars are formed before any of the planets and if so, the light emitted by a star is more ancient than the material (e.g. rocks) in planet's core/crust. The rocks are formed mere 120-170M years ago which is less than some distant stars at few hundred/thousand light years. No ? Did I miss something basic ? Thanks in advance to those who care to respond/explain/clarify.

[drlane]

Well it's really really hard to see objects in the sky that are 100s of millions of light years away. Without a telescope is impossible and it will even take a pretty good one to see galaxies that far out.

[Nitpicker]

Hi, I'm a bit confused by this statement in the explanation - "Usually it’s the rocks that are older, with their origin sentiments deposited well before light left any of the stars or nebulas you see in the sky". I thought the stars are formed before any of the planets and if so, the light emitted by a star is more ancient than the material (e.g. rocks) in planet's core/crust. The rocks are formed mere 120-170M years ago which is less than some distant stars at few hundred/thousand light years. No ? Did I miss something basic ? Thanks in advance to those who care to respond/explain/clarify.

Well, it is not really about the age of the stars, but the age of the starlight, which correlates to the distance of the stars (distance = age of starlight * speed of light). The Sun is billions of years old, but the sunlight we feel today, left the Sun only a few minutes beforehand.

[CharlesE]

ShaileshS:

The quote you're referring to compares the actual age of the foreground rocks to the travel time of the light from the stars. While one light year is a distance, it also references a the time in years the light has traveled. You're correct that the stars are much older than the foreground rocks.

[Boomer12k]

Truly awe inspiring....

:---[===] *

[HellCat]

Did you really mean "sentiments"?
Or
Sediment?

[hoohaw]

Did you really mean "sentiments"?
Or
Sediment?

The sediments have made a sentimental journey...

[geckzilla]

Did you really mean "sentiments"?
Or
Sediment?

The sediments have made a sentimental journey...

Hah.

Thanks, HellCat. I emailed Bob about it for you.

[Ann]

What a great picture! Not only does it look beautiful, but the annotated version is so much fun, too!

Ann

[Ann]

ShaileshS:

You're correct that the stars are much older than the foreground rocks.

Actually, Vega may be younger than some of the foreground rocks. At the very least, Vega is much younger than the Earth itself.

Ann

[tjjharris]

The caption includes " older, with their origin sentiments deposited well before ". Did you intend to say "sediments"?

[RJN]

Did you really mean "sentiments"?
Or
Sediment?

Oops! Thanks. Fixed it. - RJN

[rstevenson]

ShaileshS:
You're correct that the stars are much older than the foreground rocks.

Actually, Vega may be younger than some of the foreground rocks. At the very least, Vega is much younger than the Earth itself.

Current estimates make Vega about 1/10th the age of our Sun, or about 450 million years old. That seems to make it older than any rocks identified in this APOD, though younger than some rocks that can be seen elsewhere on the surface of the Earth.

Rob

[Chris Peterson]

Current estimates make Vega about 1/10th the age of our Sun, or about 450 million years old. That seems to make it older than any rocks identified in this APOD, though younger than some rocks that can be seen elsewhere on the surface of the Earth.

These are young (Eocene) rocks, so we'll see very few stars indeed that are actually younger. On the other hand, a shot like this made elsewhere, with precambrian granite perhaps, would have nearly all the bright stars (certainly most of the naked eye stars) truly younger than the rock formations, with light travel time an insignificant factor.

[Alex Conley]

Why in the world is NGC 7331 given such a large uncertainty in distance? The NED distance, compiled from 37 different distance measurements, is 14.3 +- 2.2 Mpc -- so the light travel time is 46.6 +- 7.2 million years. That's a rather smaller range than 50-500 million years -- and NGC 7331 certainly isn't far enough across to account for that range.

They may mean that NCG 7335 and 7337 are also visible in that inset, and they are much farther away -- but if so, that is rather unclear!

[Chris Peterson]

Why in the world is NGC 7331 given such a large uncertainty in distance? The NED distance, compiled from 37 different distance measurements, is 14.3 +- 2.2 Mpc -- so the light travel time is 46.6 +- 7.2 million years. That's a rather smaller range than 50-500 million years -- and NGC 7331 certainly isn't far enough across to account for that range.

They may mean that NCG 7335 and 7337 are also visible in that inset, and they are much farther away -- but if so, that is rather unclear!

I take it to mean that the three identified galaxies lie in that range, which is reasonable: ~50 million ly for NGC 7331 and several hundred million ly for the other two.

[drlane]

That is exactly right. There is a phethora of distant background galaxies that appear to be part of the group but are in fact much much further away.

[DavidLeodis]

As it must have been dark to take the image to show the astronomical features I'm confused as to how the rocks and the ground near and also some distance from them are so light coloured that they seem almost to be in daylight?

[Chris Peterson]

As it must have been dark to take the image to show the astronomical features I'm confused as to how the rocks and the ground near and also some distance from them are so light coloured that they seem almost to be in daylight?

It's a composite image constructed from a stack of different exposure times. It's also common in images like this to light the foreground with a flash or some other artificial source if natural lighting is too low.

[starsurfer]

Rob Gendler is credited with 3 inset images but I believe all 4 of them are by him.

Also below are links to closer images:

NGC 7331
North America Nebula
Eagle and Swan Nebula
Lagoon and Trifid Nebula

[Ann]

It's a joy to see this beautiful image again! Thanks to APOD Robot for providing a link to this image almost a year after it was first posted.

APOD Robot wrote:
The green bands are airglow

There seems to be pink bands as well. What are they?

All in all, this is a wonderful image!

Ann

[neufer]

Click to play embedded YouTube video.

APOD Robot wrote:

The green bands are airglow

There seems to be pink bands as well.

What are they?