Starship Asterisk*

If the corona is five light years across; than the satr itself must look larger than what it actually is. Can someone enlighten me?
Orin

edited: a link, and another /makc

orin
Could you provide relevant links? My connection here on the boat is about 26,400 kbs. So it is a bummer to try and track down abel 39. Thanks

Norval

This is caused by the brightness of the star itself.
If you look at the stars from the city, and then from the darkness of the country side, you will notice far more stars from the country side. The city lights obscure the dimmer stars. A similar thing happens when comparing the brightness of the star to the darkness of surrounding space. The light from the star obscures the surrounding darkness causing the star to appear to be larger than it really is.
(This is what causes problems when trying to locate extrasolar planets. The stars brightness obscures (overpowers) the reflected light from the surrounding planets making them unseeable.)
This causes the star to appear larger than it actually is.

Try this: Go out at night with a friend into the dark countryside. Take three flashlights of equal size (lens diameter) but different magnitudes (candlepower). Stand about 1/4 mile apart on a long straight stretch of road. (watch for cars). shine the different lights toward each other and you will notice that the more powerful light looks larger than the less powerful light even though the lenses are the same diameter. (Careful of the large candlepower light and your eyesight)

Thanks BMAONE23! Makes sense to me.
Orin

Am I the only one who doesn't see any nebula????

Saving makc the trouble:

ben wrote:Am I the only one who doesn't see any nebula????

The star is in the middle, the "bubble" around it is the nebula. A planetary nebula is created when a star in it's dying stages "puff"s off its outer layers.

Here's a little more in-depth info on planetary nebulae.

ben wrote:Am I the only one who doesn't see any nebula????

I think you need to adjust brightness of your monitor. Nebula ring is very faint in that image.

Not sure as to why it is spherical, but a great many of these faint PN's exhibit a similar structure, they are faint because they are very large and spread out, hence it's fairly logical to assume they are at a very advanced stage (old!) maybe by this time in the PN's existence the expansion has evened out from it's original hourglass shape (which many brighter pn's seem to have) and thus exhibits the sphere shape. It could also be a function of it's position reklative to us, but a good many are then similarly oriented.

i still can't see the nebulae even after adjusting the contrast and brightness why is it so?

This annotated version should help a little, the yellow borderline lies just outside the nebula limit, I have brightened the nebula a little, but this then does not give an accurate image of it's true brightness in comparison to the background, but at least you will know what to look for in the original.

These nebula are very difficult to see without using a OIII filter and a fairly large telescope (12" or more) (meaning for amateur astronomers)

k thanks

Kim wrote:Not sure as to why it is spherical, but a great many of these faint PN's exhibit a similar structure, they are faint because they are very large and spread out, hence it's fairly logical to assume they are at a very advanced stage (old!) maybe by this time in the PN's existence the expansion has evened out from it's original hourglass shape (which many brighter pn's seem to have) and thus exhibits the sphere shape. It could also be a function of it's position reklative to us, but a good many are then similarly oriented.

Planetary Nebulae are only visible for roughly 40,000 to 60,000 years. In the context of stellar evolution, this is practically a blink of an eye. Thus you can't really distinguish 'old' PNe from 'young' PNe, since if they are visible, they are all roughly the same age.

PNe ought to be spherical. The standard stellar evolution model predicts their formation from old red giants or asymptotic giants (depending on the mass of the star) puffing off their outer layers. The result is the core of the once-giant star contracting to become a white dwarf, which ionizes the expanding outer layers making them visible to us as a PN. According to the standard model, unless a star has an incredibly strong magnetic field (which is not observed), the resultant nebula should be spherical. Abell 39 is a classic example of what PNe should look like.

The question is not, "Why is Abell 39 spherical?" but rather "Why are so many others asymmetric, or axisymmetric?"

The most likely answer to this is simply an argument of binarity. Recent studies have shown that a surprisingly large number of PNe have binary star systems at their cores. This would quite easily explain the axisymmetric shapes of most PNe. The gravitational interactions between the companion stars would shape the expanding nebula.

Check out this article for more information. http://www.noao.edu/outreach/press/pr04/pr0402.html It looks like someone from Michigan Tech, where RJN and several people on this board work, was involved on the project.