h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

"It is so close (relatively speaking) that very large telescopes can discern its disk."

Can you describe this disk for me please? I'm not sure what you mean.



Ste

Hi Ste,

Most stars, no matter how powerful the telescope, only appear as tiny dots in the sky given their size compared to their vast distance from us. Even though you might have seen bright stars as globular or spiky objects in astronomy magazines, this often says more about the optics of the telescopes used than the dimensions of the stars themselves. To us here on Earth, most of them have no "size" as such. Arcturus is just slightly different, because it is a big star, and it is also relatively close to us, so the most powerful telescopes can actually discern it as a spherical object with a measurable diameter, just like we can discern the disk of the sun. It has an angular diameter of 0.0191 seconds of arc, which is very small.

Woodpigeon

Oh! that is amazing. Thanks for the explanation. I couldn't get the picture of a horizontal disk, eminating (solar-system stylee) outwards for some reason. But to be able to see the actual thing instead of a blod is cool

Thanks

Ste

blod = blob!

The possibilities of this are fairly intriguing - scientists are working on developing massive telescope arrays which will enable them to magnify objects far away, so that star-spots and planets might be clearly discerned. This is currently beyond the bounds of even the Hubble telescope. Arcturus would be a prime candidate for this when/if they ever get there.

Like, one huge array all over the globe?

Couldn't they stick a few more hubbles up there and array them together?

Something like that, yes.

I think they lost the DIY manual for Hubble . "Build your own Hubble Kit" - now *there's* an idea!

Actually, what would be really interesting would be an array on the far side of the moon, so maybe we should be investing in a "Build your own Saturn IV Rocket" kit first. Spanners, anyone?

Ooooo, an excuse to go galavanting around the moon! Pass the screwdriver mate

What would be a really great view would be to be able to look out the window of the space hotel that people have talked about there one day being in orbit. Imagine being able to see the earth far below out of one window and see the moon far below out another. Of course light pollution from earth may obscure some of the stars which is a good point in favor of a lunar observatory. Even on the highest mountaintop on earth you would still have some distortion from the air to block your view and Hubble has had it's troubles with its vision in the past. As far as an array of telescopes I seem to remember something of that idea being postulated on a science program some time back. It would have to be built out in space to be powerful enough if I recall from the program. Probably in a lagrange orbit so it wouldn't go drifting off over time.