Limits of telescopes

Kevster

Yo guys,

What exactly are the limits to what telescopes can see in the visible spectrum? Read further!... ...I read this on the BBC website recently:

"It may be the end of the next decade before we have telescopes powerful enough to directly image Earth-like planets, and reveal whether they have continents and oceans"

This made me wonder about how far we could potentially see. Is it merely a matter of building a big enough mirror and pointing it at one location for long enough? - surely not. What are the limits?

Kevin

dlofnep

It's not possible. The light emitting from a star essentially blots out any chances of actually seeing a planet, let alone any detail on it. Planets are found by examining to see if there are any objects causing the doppler effect on the respective star.

I don't think we will ever be able to see detail on an extrasolar planet, unless we send telescopes into deep space to examine them closer. I mean, this is how we currently see Pluto with the hubble telescope: http://nai.arc.nasa.gov/astrotech/candidates/images/pluto/pluto_1_large.jpg

djhaxman

dlofnep wrote: »

It's not possible. The light emitting from a star essentially blots out any chances of actually seeing a planet, let alone any detail on it. Planets are found by examining to see if there are any objects causing the doppler effect on the respective star.

I don't think we will ever be able to see detail on an extrasolar planet, unless we send telescopes into deep space to examine them closer. I mean, this is how we currently see Pluto with the hubble telescope: http://nai.arc.nasa.gov/astrotech/candidates/images/pluto/pluto_1_large.jpg

It is possible, using a coronograph to mask the light from the star. In fact it has been done

http://www.princeton.edu/main/news/archive/S25/96/87S57/index.xml?section=topstories

There are other techniques available too other than the doppler effect.

http://planetquest.jpl.nasa.gov/

dlofnep

djhaxman wrote: »

It is possible, using a coronograph to mask the light from the star. In fact it has been done

Yes, to see a dot it's possible, but it's not possible to see surface detail. I should have clarified that.

Kevster

Yeh, that's what I was thinking too, dlofnep - i.e. I have the same skepticism as you. i always knew that 'we' had managed to directly observe an extrasolar planet, but to see surface detail...? - that just seems a little too much at this point. The article I read only said that it "might" be possible in the future. There must be a limit at some point - Maybe we've already reached the limit which is why we have to use all of these other techniques to 'see' these other planets.

The example of Pluto you gave is quite good, because that's relatively clos and yet we cannot even see it clearly. Horizon is on its way to Pluto though, arriving in 2014 I believe!

Kevin

Capt'n Midnight

Am always amazed at the way telescopes can beat the limits so often.

The atmosphere moves, there is dirt in it and glare from lights. But things like adaptive optics, following a nearby star or if there isn't one a green laser, allow you to bypass many atmospheric effects. Lucky aperture allows you to pick and choose images and bypass a lot of Gaussian perturbation. Having long base lines also helps - how big is the biggest telescope in the pipeline - you will be be impressed if you don't already know.

Another technique used in audio is to graph the sound and then photoshop out the noise, classical information theory says you can't do this, but in practice you can !

Sykk

Let technology evolve. Things we're doing nowadays would have been ideas that were frowned upon 300 years ago.

-Nigel

Kevster

Sykk wrote: »

Let technology evolve. Things we're doing nowadays would have been ideas that were frowned upon 300 years ago.

-Nigel

On that note, it was recently proposed here in the UK to cut funding for 'speculative' scientific research projects (i.e. and only fund those research groups who are likely to give positive and practically beneficial results). There was a lot of upset about this obviously and it was pointed out that many great scientific discoveries in the past happened as a result of not thinking along the straight line, if you know what I mean, and instead performing research whose results may or may not prove useful.

Kevin

Capt'n Midnight

http://en.wikipedia.org/wiki/Navy_Prototype_Optical_Interferometer

large scopes in progress
http://en.wikipedia.org/wiki/Extremely_large_telescope


sadly cancelled
http://en.wikipedia.org/wiki/Overwhelmingly_Large_Telescope

It has been estimated that a telescope with a diameter of 80 meters would be able to spectroscopically analyse Earth-size planets around the 40 nearest sun-like stars.[3] As such, this telescope could help in the exploration of extrasolar planets and extraterrestrial life (because the spectrum from the planets could indicate the presence of molecules indicative of life).

Kevster

A telescope with that large a mirror couldn't be launched into orbit intact though...? It'd have to be assembled in space, but that's not possible, given hoew these mirrors are made, right?

Capt'n Midnight

adaptive optics and other knudges means that you can get better results for many purposes from ground based telescopes than from hubble and for a fraction of the price


hubble is of use because some parts of the spectrum are blocked by the earths atmosphere and because it can see very low light levels