I find this a very valuable teaching tool:

http://content5.clipmarks.com/view_clip....

It is pretty cool.

I wish it were better about indicating which images are actually photos of the objects in question and which aren't, though -- most of the images for the stars are just doctored images of the Sun. (Not a problem, it's still cool, but it could very easily give the wrong impression).

Now I knew our sun was fairly small as far as stars go, but I never realized HOW MUCH larger some of the stars were. Rather incredible.

Saw this before, quite interesting.

#3: As far as I know our sun is not particularly small, I remember something about it being 'medium-sized'. Still, the upper limit of star size is so much larger than the sun.

4>

Well, that depends on how you define things.

Small stars are much more common than big stars, but the smallest stars have a radius of about 0.1 solar radii. The biggest stars, on the other hand, are rare, but supergiants have radii of 1000 solar radii or more. So if you take a weighted average, the sun probably ends up as "medium-sized", but if you just put it on the line from smallest stars to biggest stars it's pretty close to the small end.

(I'm only talking about stars, here, not substellar objects like brown dwarfs or stellar remnants like white dwarfs and neutron stars.)

#5: Not really, the median ('lining them up and taking the middle one') would probably be smaller than the mean in this case. Only if you consider the entire range of possible sizes of stars, then plot the sun in this range would it look as small, but this is a very skewed way of looking at things.
Consider human body weight for adults: even though the range is something like 30kg* - 635kg, a 'medium sized' person weighs about 74kg and not 300kg.
* Made the lower bound up, as I could not find data on it.

... and now back to interesting scientific visualizations:
Powers of 10: http://www.youtube.com/watch?v=A2cmlhfdx...

6>

Don't put words in my mouth. I didn't use the word median because in the case of continuous values it isn't very meaningful.

What I mean is exactly what I said.

Draw a line. Put linear markings on it. Mark one endpoint "0.1 solar radii". Mark the other endpoint "1000 solar radii". This is the range of sizes of stars.

Now if you just put a third mark on it, for "1 solar radius", it will be much closer to the small end than the large end.

However if you start making a histogram of stellar radii, you will find that since there are many more small stars than large stars {1}, if you just take a sample of stars and plot their radii you will find that the sun is "medium-sized".

{1} I did my #($*&)#$ PhD dissertation on the initial mass function of stars. Don't you dare tell me I don't know what I'm talking about here.

#7: calm down. "just put it on the line from smallest stars to biggest stars" sounded kind of ambiguous to me, and could be taking all stars in the universe, sorting them to make a line from smallest star to biggest star, and then considering where the sun would be on this line. Hence, the interpretation of 'median'. I have never heard of the median not being meaningful for continuous values, having seen it applied to things like height, weight, luminance, etc.

Also, you completely ignored my criticism of the correct interpretation of your post.

These are terrific videos for the non scientist like me. Does anyone know of a video that shows the actual and apparent motions of the planets and moons. I am struggling to get that visual in my old and slow brain.

8>

I didn't realize I had to respond to everything. I responded to the parts that I disagreed with. And in your example of human body weight, I think we're in violent agreement -- 1000 solar mass stars, like 600 kg humans, are really rare.

#10: I gave two interpretations of your post, and thought neither showed that 'medium-sized' is a misnomer. Being angry(?) over one of those interpretations not being what you meant while ignoring the other one seems rather unproductive. Then again, maybe I just misinterpreted your post as disagreeing with the 'medium-sized' designation while it could have been meant as just an interesting scientific tidbit.

#9: Apparent motions from the Earth? There's planetarium software for that.
Actual motions are quite difficult to show unless you distort the scale, as the 'powers of 10' video and the image in the OP show. The planets are simply too small compared to the size of the sun, and everything is small compared to the size of the solar system. Does this help?

Message edited by its author, Aug 6, 2009, 5:36pm.

Sander314,

Thanks, both links helped. I am just trying to visualize the combined effects of the eliptic, the lunar orbit, the rotation and earth orbit, sidereal and synodic periods, precession, etc. I thought it might help to see some video, but have not found any presenting these effects of apparent motion, at least not among the many fantastic videos on YouTube.

We do have a local observatory. I really need to visit it.

Message edited by its author, Aug 6, 2009, 6:05pm.

Dear Tool...
That was "awesome" in the true meaning of the word. As Milton would have used it, not to describe a pair of jeans :-)