APOD: Herschel's Andromeda (2013 Feb 02)

[bystander]

In referring to another person besides me, “other’s” is correct.

Sadly, just saying it is so doesn't make it so, but you just keep on blissfully botching the English language. You're not the only one. Oh, wait, perhaps you're one of those that say "your not the only one".

Nobody cares any more, anyway. Why the hell should I? Carry on.

The correct possessive form for a singular other is other's, multiple others would be others'. Look it up in a dictionary or google it.

[geckzilla]

I'm sure emc's use of the word "others" was intended to be plural and so others' is correct. That is a rather tricky instance of a possessive plural pronoun.

Emc may have intended the use of "other" to only refer to one person. In this case it's awkward and that's what's causing the slip-up more than anything.

[neufer]

I'm sure emc's use of the word "others" was intended to be plural and so others' is correct. That is a rather tricky instance of a possessive plural pronoun.

Emc may have intended the use of "other" to only refer to one person. In this case it's awkward and that's what's causing the slip-up more than anything.

Emc: "It pains me to see my own errors...

• I feel relief when I see other's."

"I feel relief when I see [the errors of] other."

"I feel relief when I see [the errors of] another."

"I feel relief when I see another's."

[Beyond]

I never did very well with all that 'proper' inglish in englash class, so this thread doesn't give me any releaf at all.

[emc]

In referring to another person besides me, “other’s” is correct.

Sadly, just saying it is so doesn't make it so, but you just keep on blissfully botching the English language. You're not the only one. Oh, wait, perhaps you're one of those that say "your not the only one".

Nobody cares any more, anyway. Why the hell should I? Carry on.

Thank you Jedster1, you are right. I should have typed “others’” instead of “other’s”.

From your responses, I don't think you can help but care. And from others’ response posts, I think your statement that nobody cares is wrong.

[geckzilla]

I've found that I read straight through most errors. We're not writing English papers for our university professors. A forum like this is for informal discourse. Errors are to be expected just as one fudges speech now and then when chatting with friends. It's best not to get worked up over it just like you don't get worked up when you get tongue tied.

[Chris Peterson]

I've found that I read straight through most errors. We're not writing English papers for our university professors. A forum like this is for informal discourse. Errors are to be expected just as one fudges speech now and then when chatting with friends. It's best not to get worked up over it just like you don't get worked up when you get tongue tied.

I suggest pointing out errors in the APOD caption, since they should be fixed for posterity. Errors in subsequent discussion, however, are rarely worth pointing out. There are times where unusual errors can lead to interesting discussions about our language, of course. (This discussion of the possessive form of "other" - made somewhat confusing by the rather ambiguous usage that made it hard to tell if the word was being used as a singular or not- brings to mind the interesting case of "people", which is properly genitivized as "people's"...)

And, of course, I think it is always fair game to point out language errors in the postings of language police!

[Beyond]

Language Police Well, at least there's no phone cops here, cause there's no phones.

[Ron-Astro Pharmacist]

Help I can't figure this out. In April's 2013 Astronomy the article says that the Andromeda galaxy is moving toward Earth at 1,080,000 km/hr (Vesto Slipher's calculation cited) and is at a distance of 2,500.000 light years. The math would suggest:

a. 1,080,000 km/hr x 24 hrs/day x 364.25 days/yr x 2,500,000 years the Andromeda galaxy should be 2.36 x 10¹⁶ km closer now than it was 2.5 million years ago when the light set out.

b. If light travels 9.46 x 10¹²km/yr x 2,500,000 years, the Andromeda galaxy should be 2.36 x 10¹⁹ km distant.

If you subtract a. from b. you get that it is 1 x 10³ km from us now which can not be correct. The same article says that the Andromeda galaxy should not be here for 3.85 billion years. Some sources place the oncoming speed at half what Vesto cited but it still wouldn't be any where near correct. Where am I doing the math or logic incorrectly?

[Chris Peterson]

Help I can't figure this out. In April's 2013 Astronomy the article says that the Andromeda galaxy is moving toward Earth at 1,080,000 km/hr (Vesto Slipher's calculation cited) and is at a distance of 2,500.000 light years. The math would suggest:

a. 1,080,000 km/hr x 24 hrs/day x 364.25 days/yr x 2,500,000 years the Andromeda galaxy should be 2.36 x 10¹⁶ km closer now than it was 2.5 million years ago when the light set out.

Fine. It's gotten a couple of thousand light years closer over 2.5 million years. A fraction of a percent of its distance. (FYI, a year is 365.25 days.)

b. If light travels 9.46 x 10¹²km/yr x 2,500,000 years, the Andromeda galaxy should be 2.36 x 10¹⁹ km distant.

All you've done is convert light years to kilometers. Fine.

If you subtract a. from b. you get that it is 1 x 10³ km from us now which can not be correct. The same article says that the Andromeda galaxy should not be here for 3.85 billion years. Some sources place the oncoming speed at half what Vesto cited but it still wouldn't be any where near correct. Where am I doing the math or logic incorrectly? :?:

You might want to do that math again. 2.36 x 10¹⁹ - 2.36 x 10¹⁶ is 2.36 x 10¹⁹ km, or 2.5 million ly. You're just subtracting off that tenth of a percent found in (a), which doesn't even show up when given to two decimal places.

[MargaritaMc]

2.36 x 10¹⁹ - 2.36 x 10¹⁶ is 2.36 x 10¹⁹km, or 2.5 million ly.

Can you run that bit by me again, Chris? I am only at remedial mathematics level, so I'm probably missing something obvious.

Margarita

[Ron-Astro Pharmacist]

Thanks Chris - It's been awhile since using scientific notation on my calculator then actually doing the math. I got a wild hair after reading the article to calculate where Andromeda is now (as opposed to 2.5 million years ago when its light was emitted) at its calculated speed moving toward us.

To reference it, I thought I could calculate how far away it was using light speed x elapsed time. One being much slower than the other, I thought the difference would be much greater than my calculation showed. I knew it had to be a math error but I could not see it.

Thanks for taking a look

[MargaritaMc]

I was intrigued by this proposed merger, so looked up the BBC science news site.

http://bbc.co.uk/news/science-environment-18285583
It has long been known that the two galaxies have been heading in the general direction of each other.

They are separated by about 2.5 million light-years, but are converging at something like 400,000km/h (250,000mph). The new Hubble data provides fresh insight on when and how a union is likely to unfold.

[Chris Peterson]

2.36 x 10¹⁹ - 2.36 x 10¹⁶ is 2.36 x 10¹⁹km, or 2.5 million ly.

Can you run that bit by me again, Chris? I am only at remedial mathematics level, so I'm probably missing something obvious.

The second number is only a thousandth of the first. It's like subtracting one from a thousand. The difference isn't apparent when the number is rounded two just two places.

[MargaritaMc]

2.36 x 10¹⁹ - 2.36 x 10¹⁶ is 2.36 x 10¹⁹km, or 2.5 million ly.

Can you run that bit by me again, Chris? I am only at remedial mathematics level, so I'm probably missing something obvious.

The second number is only a thousandth of the first. It's like subtracting one from a thousand. The difference isn't apparent when the number is rounded two just two places.

After I'd posted my question, I decided to do the sums, but just using the speeds/distances in km/hr.

Light in one hour travels. ......... 1,080,000,000 km

The Andromeda galaxy, in the figures first given, travels .... 1,080,000 km

This is an excellent visual exemplar of just why one does not subtract the powers/exponents in scientific notation!

The odd thing is that this is totally obvious when one is using exponents in everyday life: it is a no-brainer that if you have 5² to deduct from 5³, one doesn't end up with 5¹! But that is because the numbers are within human experience of the dimensions we live within.

Thanks for the maths lesson, Chris and Ron!

Margarita

[alter-ego]

 

While there is no up or down in space, every time I see the Andromeda or other galaxy at a steep angle like this I wonder are we looking up at the bottom or down at the top. In other words is the edge to the right top closer to us or is it the bottom left and at that distance can we really know for sure?

It looks to me like the left hand edge is closer. You can see faint blue and green blotches of hotter gas to the lower left of that edge, against the blackness of intergalactic space. These look like small objects orbiting the galaxy -- globular clusters perhaps? On the opposite right hand edge, the faint blue and green blotches are superimposed against the much more saturated red spirals, as if they are seen against the background of the galactic disk. Any faint blue and green splotches behind the galactic disk would be hidden by the disk itself.

That's just how it looks to me. Maybe somebody else actually knows for sure.
...

Finally we now know.
Over the years since this APOD, I've been keeping an eye out for a definitive answer. At the time of this post, two competing ideas were: 1) The right (NW) edge because the inner dust lane(s) visible,

We can see that the western (right) side of M31 is closer to us, by the fact that the dark dust lanes belonging to the inner spiral arms show up in silhouette against the nucleus on that side only.

and 2) The GALEX UV image suggests the left edge is closer because the UV sources are brighter from less extinction. Even models/animations that simulate the present spiral structure and M32 didn't agree. In 2015, Dr. Marion Dierickx (Signatures of the M31-M32 Galactic Collision (2014)) responded to my M31 rotation question. He compared several publications, but his summary succinct:

The questions you ask are very relevant. In our work on M31 we found that there is quite a bit of confusion even amongst specialists about the rotation and spiral structure. Below I've pasted notes that my collaborator Laura Blecha wrote on on 3/30/14. As you can see it's quite a mess. The high inclination angle of the disk makes any attempt at deprojection difficult.

In the pair below left, the "normal" visual component does tend to show more silhouetting on the right edge, the GALEX image on the right:
 

Click to view full size image 1 or image 2

GALEX

---

Both concepts are good and supported by observations, but both rely on assumptions: M31 is warped and it's not clear that more the nearest edge has to be more transparent, and concluding the closer edge by the silhouette is based on visual interpretation. Since spiral arms can be leading or trailing, interpreting rotation direction from spiral structure is also not conclusive (exacerbated, as stated, by M31's high inclination angle).

Well the answer is, in fact, the right edge. GAIA has provided the data to better predict local group kinetics (and galactic rotation). http://asterisk.apod.com/viewtopic.php?f=31&t=39150
I was pleasantly surprised. I wasn't thinking about GAIA measuring stars in other galaxies. Instead I thought precise Earth-based precise water maser tracking would provide the answer. (Tangential motion ~70 µarcsec/year)
Proper Motion of the Andromeda Galaxy: The Keystone of Local Group Dynamics Proper Motion (2011).

Using the M31 velocity field, and the convenient S&T graphic, the definitive counterclockwise rotation identifies the right edge is the closest to the Milky Way.
 

M31 Rotation - GAIA

M31 Velocity Field