Stellar?

[imarcs]

I thought i had read enough now for things to start falling into place and to be honest a lot more of what i'm reading now makes more sense especially in relation to where everything is.

However, i keep reading a certain phrase that i'm not sure about in books and sometimes on here.

For example the opposing comments - "The object looks non-stellar" or "the object takes on a stellar appearance"

Is it really that simple that these phrases mean " the object looks like it doesn't consist of stars", and "the object does look like it consists of stars"

Thanks for any clarification (preparing for a embarrassingly simple answer) :-)

[JimStan]

The difference can be very subtile, but basically the phrases are used to differentiate between a star, and nebulas or galaxies.

In theory, you can push the magnification of your scope as high as you have eyepieces, but the image of a star will be, as closely as possible, a point of light. Of course, that is theoretical and the point of light may tend to spread out under excessive magnification! But point the scope at Jupiter, for instance, and it will definately be "non-steller" in appearance! In fact, it should start appearing like a little round ball, with a very low magnification. Higher magnification will reveal the atmospheric bands near the surface of the planet, and even the 4 largest moons will start to appear "non-stellar" if conditions are good enough.

Other objects, such as "The Great Nebula" in Orion, or "The great Andromeda Galaxy" should take on a shape that is certainly NOT a pinpoint of light, and this shape should be redilly apparent at fairly low magnifictions.

Even objects that are composed almost totally of stars, can appear "non-stellar" under the right circumstances. M13, the globular cluster in Hercules, is almost 100 % composed of stars, but when viewed with moderate magnification, it appears like a vast collection of bees swarming around a streetlight ! Open clusters that are too far away and dim will appear "non-stellar" if they are too dim to reveal individual stars for a particular telescope. Bear in mind that some of these will appear "non-stellar" in, for instance, a pair of binoculars, but will definately appear to have thousands of individual star-points in a larger scope, such as a 17 inch "Obsession"

"Planetary Nebula" got their name from early telescopic astronomers, because they looked much like planets. They were not large well-defined clouds in the sky, but they certainly looked "non-stellar" and resembled planets in the poor telescopes that the early astronomers had to use.

Clear Skies ! Jim S.

[imarcs]

Perfect. Thanks a million Jim!!

[Vali x]

good to know Jim..thanks

[acey]

"stellar": point-like

"non-stellar": extended

"fully resolved": seen to consist of stars

"partly resolved": seen to contain some stars, but also fuzzy areas.

"not resolved": fuzzy all over

In the case of very faint objects it can be hard to distinguish between stellar and non-stellar: the NGC contains many objects that are actually just faint stars, which observers mistakenly took to be non-stellar.