Ask an Astrophysicist - APOD's Dr. Jerry Bonnell

[Ann]

I love the Buffer Brown and Tighe image!

Ann

[Beyond]

Ok Dr. Jerry Bonnell - Now that you have asked and answered a question that you would have liked to have been asked but never was, could you please explain the answer that you gave?? I can not find anything anywhere that gets rid of a pant leg tugging feeling that i have about your answer.

[Bobby Woods]

How many people do you think, like myself, read the APOD every single day?

Kind regards.

[neufer]

How many people do you think, like myself, read the APOD every single day?

There is probably a difference between
the number of people who actually read the APOD and
the number of people who just look at the pictures
(much as with Playboy magazine).

[Ann]

There have been 1275 views of this thread. 1275, what a great astronomical number! 1275, as in NGC 1275, the remarkable Perseus A galaxy.

Click to view full size image

This image was APOD on July 25, 2005, in case you are wondering!

Ann

[Beyond]

Ann, that was before my time. To me NGC 1275 looks like >The Attack of The Pinkish-Red thing!

[Curiosity]

Why are there no green stars?

[Chris Peterson]

Why are there no green stars?

The color of stars is mainly determined by their temperatures- they are approximately black body emitters, and the shape of a black body spectrum, combined with the responsivity of our eyes, means that there is no temperature that can produce green. There is a temperature where the peak wavelength is green (in fact, that's pretty close to our own Sun), but when mixed with all the other wavelengths, our eye sees something else. When you heat something up, from cold to hot it goes red-orange-yellow-white, with a hint of blue at the hottest end. Gas in the stellar envelope, or in the intervening space, can result in a shift of color, as can scattering and absorption by dust. But none of these mechanisms can really make a star look green.

[bystander]

Why are there no green stars?

They keep all the "green" stars hidden behind cloaks of dust and gas so that the only stars you see are mature stars that have been aged properly and are no longer considered "green".

[Chris Peterson]

They keep all the "green" stars hidden behind cloaks of dust and gas so that the only stars you see are mature stars that have been aged properly and are no longer considered "green". :lol:

Now I'm confused. Isn't the Moon made of well-aged green cheese? Are there different rules for stars and planetary satellites?

[Beyond]

Why are there no green stars?

They keep all the "green" stars hidden behind cloaks of dust and gas so that the only stars you see are mature stars that have been aged properly and are no longer considered "green".

In that case, are all the really "old" stars grey and hiding in the dust and stuff also

[neufer]

Why are there no green stars?

There is a temperature where the peak wavelength is green (in fact, that's pretty close to our own Sun),
but when mixed with all the other wavelengths, our eye sees something else.

But when separated from all the other wavelengths, our eye sees green:

http://asterisk.apod.com/vie ... sh#p131453

[Chris Peterson]

But when separated from all the other wavelengths, our eye sees green...

Of course. For all the images we see on APOD, vastly more astronomical data is collected using spectroscopes, which do show precisely how much green is really there.

For that matter, you can view the stars using a green filter, and see which ones have lots of green and which have little.

[neufer]

A horse is a horse...

Of course.

[bystander]

They keep all the "green" stars hidden behind cloaks of dust and gas so that the only stars you see are mature stars that have been aged properly and are no longer considered "green".

Now I'm confused. Isn't the Moon made of well-aged green cheese? Are there different rules for stars and planetary satellites?

Same rules apply, the green cheese the moon is made of is ripe (mature) green cheese not "green" green cheese, unless, of course, it's a blue moon, then it's made of ripe bleu cheese (not "green" bleu cheese).

[bystander]

A horse is a horse...

Of course.

Of course, and no one can talk to a horse, of course.
That is, of course, unless the horse is the infamous Equine Locutionist.

[Curiosity]

They keep all the "green" stars hidden behind cloaks of dust and gas so that the only stars you see are mature stars that have been aged properly and are no longer considered "green".

Now I'm confused. Isn't the Moon made of well-aged green cheese? Are there different rules for stars and planetary satellites?

Re: Why are there no green stars?
Thanks, Cris and bystander, for your prompt and illuminating answers. I admit being still a greenhorn in astronomy. When I was a boy, 60 years ago, all stars were "golden" to me until my grandfather taught me to find Mars, which, I had to admit, was more reddish.
Meanwhile my sense of decorous diversity in the universe is pleased looking at the lovely greenish yellow of the Lemon slice nebula, IC 3568, which I discovered in the Wikipedia: http://en.wikipedia.org/wiki/Lemon_slice_nebula

Curiosity

[Beyond]

Lemon slice nebula,IC3568

Hey, thanks curiosity. I already knew Space was NUTS!!, but i had no idea that it was also Fruity!!

[JeanTate]

Well, delaying my decision to register and participate in posting here means I missed the chance to ask questions in this thread!

Just in case, though, here's one:

What do you think of the various citizen science projects that anyone (with a decent internet) connection can now join? Do you have any favorites?

OK, two questions.

How likely do you think it is that a new class of astronomical object will be discovered, from analyses of the data from Fermi? By analogy, RRATs were recently discovered by radio astronomers.

[bystander]

Well, delaying my decision to register and participate in posting here means I missed the chance to ask questions in this thread!

Just in case, though, here's one:

What do you think of the various citizen science projects that anyone (with a decent internet) connection can now join? Do you have any favorites?

OK, two questions.

How likely do you think it is that a new class of astronomical object will be discovered, from analyses of the data from Fermi? By analogy, RRATs were recently discovered by radio astronomers.

Good questions, both. I'll forward them to Dr. Bonnell, but I promise nothing.

[geckzilla]

Locked the thread and split a reply regarding comet ISON from this thread to a new topic since this interview is over.
http://asterisk.apod.com/viewtopic.php?f=8&t=32332