APOD: Star Size Comparisons (2013 Jun 06)

Comments and questions about the APOD on the main view screen.
ro-star

Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by ro-star » Fri Jun 07, 2013 12:59 pm

TheMiddaySun wrote:Am I the only one to recognize that the moon was rotating?? The moon does not rotate on its axis. We are presented with the same face of the moon at all times. Hence the saying..."Dark Side of the Moon"
the moon rotates on its axis at the same rate that it orbits the earth so one orbit = 1 rotation; this special case is called tidally locked, and is the case for all major moons in the solar system, such as Callisto, Ganymede, Io, Titan and so on, in fact all these I enumerated here are bigger than our moon;

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Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by rstevenson » Fri Jun 07, 2013 2:08 pm

New Rule: If you're going to start a post with "Am I the only one to recognize that...", you should stop and do a little research. Because you shouldn't be the only one to recognize something, unless you're a leading expert in the field. :ssmile:

Rob

waterlrl

Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by waterlrl » Fri Jun 07, 2013 2:41 pm

The video gives the impression that the Sun is a small star. This is not so. The Sun is larger than 90% of the stars in our local section of the Milky Way, and lies about midway in size between the smallest and largest stars.

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Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by Chris Peterson » Fri Jun 07, 2013 2:52 pm

waterlrl wrote:The video gives the impression that the Sun is a small star. This is not so. The Sun is larger than 90% of the stars in our local section of the Milky Way, and lies about midway in size between the smallest and largest stars.
No, the Sun is a small star. The smallest are around 10% its size; the largest are more than 1000 times larger. This video only looks at the absolute size range, not the size distribution. Of course, there are many more small stars, but that's not the point.
Chris

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Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by bystander » Fri Jun 07, 2013 2:58 pm

TheMiddaySun wrote:Am I the only one to recognize that the moon was rotating?? The moon does not rotate on its axis. We are presented with the same face of the moon at all times. Hence the saying..."Dark Side of the Moon"
The "far side of the Moon" (the side not facing Earth) is not the "dark side of the Moon". The side not facing the Sun is always changing. That is why we get Lunar phases.
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alive to the gentle breeze of communication, and please stop being such a jerk.
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Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by neufer » Fri Jun 07, 2013 3:57 pm

bystander wrote:
TheMiddaySun wrote:
Am I the only one to recognize that the moon was rotating?? The moon does not rotate on its axis. We are presented with the same face of the moon at all times. Hence the saying..."Dark Side of the Moon"
The "far side of the Moon" (the side not facing Earth) is not the "dark side of the Moon". The side not facing the Sun is always changing. That is why we get Lunar phases.
Image
http://en.wikipedia.org/wiki/Dark_side_of_the_Moon wrote:
<<The dark side of the Moon can refer to the far side of the Moon that is permanently turned away from the Earth (although it receives approximately the same amount of light as the near side of the moon)>>
Dark, a. [OE. dark, derk, deork, AS. dearc, deorc; cf. Gael. & Ir. dorch, dorcha, dark, black, dusky.]

1. Destitute, or partially destitute, of light; not receiving, reflecting, or radiating light; wholly or partially black, or of some deep shade of color; not light-colored; as, a dark room; a dark day; dark cloth; dark paint; a dark complexion.

2. Not clear to the understanding; not easily through; obscure; mysterious; hidden.
:arrow:
---------------------------------------------------------------------------
    • Love's Labour's Lost Act 5, Scene 2
    ROSALINE: What's your dark meaning, mouse, of this light word?

    KATHARINE: A light condition in a beauty dark.

    ROSALINE: We need more light to find your meaning out.

    KATHARINE: You'll mar the light by taking it in snuff;
    Therefore I'll darkly end the argument.

    ROSALINE: Look what you do, you do it still i' the dark.

    KATHARINE: So do not you, for you are a light wench.

    ROSALINE: Indeed I weigh not you, and therefore light.
Art Neuendorffer

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Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by JohnD » Fri Jun 07, 2013 4:50 pm

TheMiddaySun wrote:Am I the only one to recognize that the moon was rotating?? The moon does not rotate on its axis. We are presented with the same face of the moon at all times. Hence the saying..."Dark Side of the Moon"
I was wrong about the Black Hole, but I'm sure I'm right about the Moon!
The Moon does rotate, it turns to keep the same face towards the Earth at all times, save for a little libration.
Its rotation is "tidally locked" to its orbit.

A demonstration. This won't work if you hold the apple yourself, Midday, but have someone hold an apple (or a football!!!) and walk around you, without turning, keeping their face towards one direction all the time. You will see all sides of them and the apple. Only if you allow them to turn as they move can the keep their face towrads you and hide the far side of the apple.


Oops, now I see that ro-star got there first. Never mind.
John

Rusty Brown

Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by Rusty Brown » Fri Jun 07, 2013 5:16 pm

jrzedevl wrote:
Deesqrd wrote:Planets and Sun are rotating in reverse.
Either that or they're upside down :)
They're not upside down. Look at Earth, for example. The continents are in their customary orientation. Somebody dropped the rocky and watery ball big time on this one.
RB in Canada

Planetarian

Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by Planetarian » Fri Jun 07, 2013 10:41 pm

Venus is spinning correctly I believe

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Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by neufer » Sat Jun 08, 2013 2:00 am

Planetarian wrote:
Venus is spinning correctly I believe
Yes...but backward spinning planets with provocative nomenclatures should have been excluded from the line-up in favor of their prettier blue twins with larger orbits (and large moons). (Which is basically why Uranus was excluded.)
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Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by Beyond » Sat Jun 08, 2013 2:58 am

Uranus is sort of on the backside of the solar system, isn't it :?:
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Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by rochelimit » Sat Jun 08, 2013 12:17 pm

Inaccuracies:

Venus's atmosphere should be included!
Rotation! like clockwise Venus, but that doesn't really matter
Saturn's bulge should be squat, ellipse like, instead of a perfect sphere
Why forget Uranus? but that doesn't really matter

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Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by Chris Peterson » Sat Jun 08, 2013 2:17 pm

rochelimit wrote:Inaccuracies:

Venus's atmosphere should be included!
Rotation! like clockwise Venus, but that doesn't really matter
Saturn's bulge should be squat, ellipse like, instead of a perfect sphere
Why forget Uranus? but that doesn't really matter
To bad, however, that you entirely missed the point of the video! Ever heard the one about the forest and the trees?
Chris

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Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by neufer » Sat Jun 08, 2013 2:38 pm

Chris Peterson wrote:
rochelimit wrote:Inaccuracies:

Venus's atmosphere should be included!
Rotation! like clockwise Venus, but that doesn't really matter
Saturn's bulge should be squat, ellipse like, instead of a perfect sphere
Why forget Uranus? but that doesn't really matter
To bad, however, that you entirely missed the point of the video! Ever heard the one about the forest and the trees?
  • Nevertheless, the APOD was asking for "inaccuracies" (if not "inconsistencies"):
Explanation: ... Although an inspiring learning tool that is mostly accurate, APOD readers are encouraged to complete the learning experience -- and possibly help make future versions more accurate -- by pointing out slight inaccuracies in the video.
Art Neuendorffer

mttopman

Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by mttopman » Sat Jun 08, 2013 3:27 pm

isn't "no, you are not the center of the universe" a double negative? So we are the center after all. Go figure :)

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Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by Chris Peterson » Sat Jun 08, 2013 3:41 pm

mttopman wrote:isn't "no, you are not the center of the universe" a double negative? So we are the center after all. Go figure :)
No, "no, you are not the center of the universe" is not a double negative.

And indeed, we are at the center of the Universe, both geometrically and in terms of expansion. But we are not at the center figuratively, in the sense of our importance (except to ourselves). And it's pretty clear the author was using that latter sense.
Chris

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Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by bystander » Sat Jun 08, 2013 3:48 pm

mttopman wrote:isn't "no, you are not the center of the universe" a double negative?
I guess it would depend on what the original question was. If the original question was "Am I the center of the Universe?", then the answer to your question is "Yes, it isn't a double negative." On the other hand, if the original question was "Am I not the center of the Universe?", then your answer would be "No, it is a double negative." But in that case the correct response to the original question would have been "Yes, you are not the center of the universe."
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Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by Anthony Barreiro » Sat Jun 08, 2013 6:22 pm

TheMiddaySun wrote:Am I the only one to recognize that the moon was rotating?? The moon does not rotate on its axis. We are presented with the same face of the moon at all times. Hence the saying..."Dark Side of the Moon"
The Moon rotates once each month. http://curious.astro.cornell.edu/questi ... number=142
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Star sizes

Post by Awda » Mon Jun 10, 2013 2:58 am

Excellent video to get people thinking. But if we want to engage the public into looking up and wondering about where we are and how we fit in, we'll have to do away with posts from the likes of "Bergerac". It's that kind of quasi-academic piffle that will stifle today's students from becoming tomorrow's visionaries.

soad22

Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by soad22 » Mon Jun 10, 2013 10:26 am

yannick wrote:There is an inaccuracy near the end of the movie: I am indeed the center of the universe.
Center of your observable universe :wink:

DougHuggem

Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by DougHuggem » Mon Jun 10, 2013 12:45 pm

JohnD wrote:Hugo,
By definition, a Black Hole has no size. It is a point in space with no diameter at all.
Perhaps a BH should be the focus of a similar size comparison video going smaller rather than larger.
This video ends at the Plank length - a BH should be smaller than that!
https://www.youtube.com/watch?v=MKtfBd8QnYE

John
I would assume it was intended that the black hole's event horizon diameter be used as the basis for comparison

felixfelixby

Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by felixfelixby » Mon Jun 10, 2013 2:33 pm

diametr, km 2 800 000 000
circle lenth, formula diam.*3,14159
distance, km 8 796 452 000
hours in a day 24
velocity 900
distane per day, km 21 600
days in a year 365
distane per year, km 7 884 000
trip duration, years 1 116

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Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by neufer » Mon Jun 10, 2013 2:41 pm

felixfelixby wrote:diametr, km 2 800 000 000
circle lenth, formula diam.*3,14159
distance, km 8 796 452 000
hours in a day 24
velocity 900
distane per day, km 21 600
days in a year 365
distane per year, km 7 884 000
trip duration, years 1 116
That's only if there are no flight delays.
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Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by Chris Peterson » Mon Jun 10, 2013 2:42 pm

soad22 wrote:
yannick wrote:There is an inaccuracy near the end of the movie: I am indeed the center of the universe.
Center of your observable universe :wink:
No, physically at the geometric center of the entire Universe. That is almost certainly accurate for every 3D point in the spatial universe.
Chris

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Re: APOD: Star Size Comparisons (2013 Jun 06)

Post by neufer » Mon Jun 10, 2013 3:00 pm

Chris Peterson wrote:
soad22 wrote:
yannick wrote:
There is an inaccuracy near the end of the movie: I am indeed the center of the universe.
Center of your observable universe :wink:
No, physically at the geometric center of the entire Universe. That is almost certainly accurate for every 3D point in the spatial universe.
But, in the case of the entire Universe the term "center" has no meaning.

Whereas, the center of yannick's universe does have a meaning.

(Say "the center of yannick's universe" five times fast.)
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