APOD: Rubin's Galaxy (2020 Jan 25)

Comments and questions about the APOD on the main view screen.
sherylbrock
Asternaut
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Joined: Sun Oct 11, 2020 3:45 pm

Re: APOD: Rubin's Galaxy (2020 Jan 25)

Post by sherylbrock » Sun Oct 11, 2020 3:49 pm

Ann wrote:
Tue Jan 28, 2020 1:26 am
Chris Peterson wrote:
Tue Jan 28, 2020 12:38 am
Guest wrote:
Tue Jan 28, 2020 12:28 am


C = r(squared) x pi
C = πD. If it is 800,000 ly across (which I'm doubtful is accurate) its circumference is about 2.4 million ly. The formula you give is for area (although the meaning of area is a bit ambiguous for something which is shaped like a combination of a spheroid and a disc).

And that area would be 502 billion square ly, not trillion. (1 billion = 109.)

Visible disk (220,000 ly) of Andromeda Galaxy, vs halo (2 million ly).
Credits: NASA/STScI. Full size here.
As Chris said, it seems improbable that the radius of UGC 2885 is 800,000 light-years across. But its true radius does not appear to be well known. NASA/ESA claimed that it is 2.5 times wider than the Milky Way (which would make it perhaps some 250,000 light-years across), whereas Wikipedia wrote that it is 463,000 light-years across.

But UGC 2885 might actually be at least 800,000 light-years across, if we take its halo intoappvalleyaccount. Being an isolated galaxy in space, it is sure to have a halo. Our neighbour Andromeda, which is not isolated in space, has a huge halo. See the picture.

On a different note, different sources disagree on how wide the visible disk of Andromeda is. According to Wikipedia, its diameter is 220,000 light-years, but according to NASA.gov, its halo is just 6 times wider than its visible disk, even though the illustration at right suggests that the halo is 2 million light-years across.

In any case, if we include the halo of UGC 2885 its diameter might well be 800,000 light-years.

Ann
Great info Ann. Thanks for sharing this...

Regards,
Sherryl

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Ann
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Re: APOD: Rubin's Galaxy (2020 Jan 25)

Post by Ann » Sun Oct 11, 2020 4:15 pm

sherylbrock wrote:
Sun Oct 11, 2020 3:49 pm
Ann wrote:
Tue Jan 28, 2020 1:26 am
Chris Peterson wrote:
Tue Jan 28, 2020 12:38 am


C = πD. If it is 800,000 ly across (which I'm doubtful is accurate) its circumference is about 2.4 million ly. The formula you give is for area (although the meaning of area is a bit ambiguous for something which is shaped like a combination of a spheroid and a disc).

And that area would be 502 billion square ly, not trillion. (1 billion = 109.)

Visible disk (220,000 ly) of Andromeda Galaxy, vs halo (2 million ly).
Credits: NASA/STScI. Full size here.
As Chris said, it seems improbable that the radius of UGC 2885 is 800,000 light-years across. But its true radius does not appear to be well known. NASA/ESA claimed that it is 2.5 times wider than the Milky Way (which would make it perhaps some 250,000 light-years across), whereas Wikipedia wrote that it is 463,000 light-years across.

But UGC 2885 might actually be at least 800,000 light-years across, if we take its halo intoappvalleyaccount. Being an isolated galaxy in space, it is sure to have a halo. Our neighbour Andromeda, which is not isolated in space, has a huge halo. See the picture.

On a different note, different sources disagree on how wide the visible disk of Andromeda is. According to Wikipedia, its diameter is 220,000 light-years, but according to NASA.gov, its halo is just 6 times wider than its visible disk, even though the illustration at right suggests that the halo is 2 million light-years across.

In any case, if we include the halo of UGC 2885 its diameter might well be 800,000 light-years.

Ann
Great info Ann. Thanks for sharing this...

Regards,
Sherryl
You're welcome, Sherryl, and welcome to Starship Asterisk*! :D

Ann
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