APOD: Lynds Dark Nebula 1251 (2016 Sep 30)

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Expand view Topic review: APOD: Lynds Dark Nebula 1251 (2016 Sep 30)

Re: APOD: Lynds Dark Nebula 1251 (2016 Sep 30)

by Chris Peterson » Sat Oct 01, 2016 3:43 am

alter-ego wrote:
Chris Peterson wrote:
FLPhotoCatcher wrote:The description says that the Nebula is "drifting above the plane of our Milky Way galaxy." But wouldn't it be orbiting the Milky Way like our solar system is? In other words, wouldn't it move "up" and "down" through the plane of the galaxy?
Indeed, it is in orbit around the center of the Milky Way. Virtually everything making up our galaxy is either above or below the galactic plane. LDN 1251 is approximately 250 ly above the plane, which means it is well inside the thin stellar disk of the galaxy. Not above the galaxy, just above the central plane (as is the Sun, which could be as much as 100 ly above it).

So this nebula is on a very slightly inclined ellipical orbit which over more than 200 million years would take it around the Milky Way, half of the time above the plane and half of the time below. Of course, the lifetime of nebulas like this is only a fraction of a galactic year, so this one will spend its entire life above the galactic plane. But as you say, orbiting, not drifting.
An unperturbed elliptical orbit is most likely not the case. The mass density gradient about the galactic plane results in a separate period for crossing the plane. In the Sun's case, it crosses the plane roughly every 30 million years.
True, but it still spends about the same amount of time on each side. And this nebula will likely spend its entire existence on just one side.

Re: APOD: Lynds Dark Nebula 1251 (2016 Sep 30)

by alter-ego » Sat Oct 01, 2016 3:39 am

Chris Peterson wrote:
FLPhotoCatcher wrote:The description says that the Nebula is "drifting above the plane of our Milky Way galaxy." But wouldn't it be orbiting the Milky Way like our solar system is? In other words, wouldn't it move "up" and "down" through the plane of the galaxy?
Indeed, it is in orbit around the center of the Milky Way. Virtually everything making up our galaxy is either above or below the galactic plane. LDN 1251 is approximately 250 ly above the plane, which means it is well inside the thin stellar disk of the galaxy. Not above the galaxy, just above the central plane (as is the Sun, which could be as much as 100 ly above it).

So this nebula is on a very slightly inclined ellipical orbit which over more than 200 million years would take it around the Milky Way, half of the time above the plane and half of the time below. Of course, the lifetime of nebulas like this is only a fraction of a galactic year, so this one will spend its entire life above the galactic plane. But as you say, orbiting, not drifting.
An unperturbed elliptical orbit is most likely not the case. The mass density gradient about the galactic plane results in a separate period for crossing the plane. In the Sun's case, it crosses the plane roughly every 30 million years.

Re: APOD: Lynds Dark Nebula 1251 (2016 Sep 30)

by FLPhotoCatcher » Fri Sep 30, 2016 6:40 pm

Thanks Chris. I wasn't sure if the nebula was held "up" by the light pressure or 'solar wind' of the stars of the Milky Way.

Re: APOD: Lynds Dark Nebula 1251 (2016 Sep 30)

by Chris Peterson » Fri Sep 30, 2016 4:40 pm

FLPhotoCatcher wrote:The description says that the Nebula is "drifting above the plane of our Milky Way galaxy." But wouldn't it be orbiting the Milky Way like our solar system is? In other words, wouldn't it move "up" and "down" through the plane of the galaxy?
Indeed, it is in orbit around the center of the Milky Way. Virtually everything making up our galaxy is either above or below the galactic plane. LDN 1251 is approximately 250 ly above the plane, which means it is well inside the thin stellar disk of the galaxy. Not above the galaxy, just above the central plane (as is the Sun, which could be as much as 100 ly above it).

So this nebula is on a very slightly inclined ellipical orbit which over more than 200 million years would take it around the Milky Way, half of the time above the plane and half of the time below. Of course, the lifetime of nebulas like this is only a fraction of a galactic year, so this one will spend its entire life above the galactic plane. But as you say, orbiting, not drifting.

Re: APOD: Lynds Dark Nebula 1251 (2016 Sep 30)

by Fred the Cat » Fri Sep 30, 2016 3:04 pm

As this previous APOD shows another Cepheus flare region with the "core of the dark cloud collapsing" and "likely a binary star system in the early stages of formation". The process of multiple star formations as opposed to single star formation is captivating.

It seems today's porpoise has a purpose as it swims through Cepheus. :roll:

Re: APOD: Lynds Dark Nebula 1251 (2016 Sep 30)

by FLPhotoCatcher » Fri Sep 30, 2016 2:14 pm

The description says that the Nebula is "drifting above the plane of our Milky Way galaxy." But wouldn't it be orbiting the Milky Way like our solar system is? In other words, wouldn't it move "up" and "down" through the plane of the galaxy?

Re: APOD: Lynds Dark Nebula 1251 (2016 Sep 30)

by Ann » Fri Sep 30, 2016 5:34 am

Boomer12k wrote:The "Dark Fish" nebula...me thinkest...

Wonderful shot.
:---[===] *
I saw the fish, too! :D

But perhaps it is a spaceship-fish. :rocketship:

Ann

Re: APOD: Lynds Dark Nebula 1251 (2016 Sep 30)

by Boomer12k » Fri Sep 30, 2016 5:13 am

The "Dark Fish" nebula...me thinkest...

Wonderful shot.
:---[===] *

Re: APOD: Lynds Dark Nebula 1251 (2016 Sep 30)

by geckzilla » Fri Sep 30, 2016 3:07 am

Ann wrote:The APOD of September 30, 2016 is here already? :shock:

Well, nice image. Without dust clouds in the Milky Way, there would be no more star (and planet) formation.
It happened a couple weeks or so ago, too, but it was so much earlier in the day that I deleted the thread and the APOD got sent back to the staging area.
Ann wrote:
APOD Robot wrote:
the telltale reddish glow from scattered Herbig-Haro objects seen in this sharp image
Can't see any reddish glow, sorry.
They're rather small.
HH.jpg
HH.jpg (27.4 KiB) Viewed 1890 times

Re: APOD: Lynds Dark Nebula 1251 (2016 Sep 30)

by Ann » Fri Sep 30, 2016 12:29 am

The APOD of September 30, 2016 is here already? :shock:

Well, nice image. Without dust clouds in the Milky Way, there would be no more star (and planet) formation.
APOD Robot wrote:
the telltale reddish glow from scattered Herbig-Haro objects seen in this sharp image
Can't see any reddish glow, sorry.

Ann

APOD: Lynds Dark Nebula 1251 (2016 Sep 30)

by APOD Robot » Thu Sep 29, 2016 8:35 pm

Image Lynds Dark Nebula 1251

Explanation: Stars are forming in Lynds Dark Nebula (LDN) 1251. About 1,000 light-years away, the dusty molecular cloud is part of a complex of dark nebulae mapped toward the Cepheus flare region, drifting above the plane of our Milky Way galaxy. Across the spectrum, astronomical explorations of the obscuring interstellar clouds reveal energetic shocks and outflows associated with newborn stars, including the telltale reddish glow from scattered Herbig-Haro objects seen in this sharp image. Distant background galaxies also lurk on the scene, visually buried behind the dusty expanse. The deep telescopic field of view spans about two full moons on the sky, or 17 light-years at the estimated distance of LDN 1251.

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