Expert: Tom Whiting - 7/5/2011

Question
QUESTION: Sir,
I just want to ask that how come the telescope in space like Hubble can magnify and clarify  the light coming from million of light years away and show us a very amazing and real photo.

ANSWER: Hi Jimmy,
Since our atmosphere limits Earth-based telescopes to about 1 arc-second resolution, or on a very good steady night 0.5 arc-second resolution, the Hubble in space (no air or atmosphere) can resolve images down to it's design limit of... I'm not sure of the number, but it would be like 0.0001 arc-second resolution.  It doesn't reside at the bottom of a "swimming pool"  (our atmosphere) like all us other observers on the Earth's surface. That's the only difference, but it's a BIG difference, thus the cost to put a telescope in space is worth it. (An incoming image is always perfectly clear... but with Hubble there is no atmosphere to destroy that perfect clarity.)   As far as magnification, all telescopes can do that, no big deal there.
Clear Skies,
Tom Whiting
Erie, PA USA

---------- FOLLOW-UP ----------

QUESTION: Can u plz explain what is arc-second resolution..

Answer
Yes, it's an angular measurement (which in turn defines resolution)  so we don't have to worry about the actual linear distance between 2 close points of light in the sky, or even the distance to the object.  I'm sure you are familiar with a 90 degree angle, a 45 degree, then down to only a 1 degree angle... a very small angle for normal purposes but a huge angle in the night sky.  (The moon and sun's apparent diameters are about a 1/2 degree angle).
Anyway, one degree is divided into 60 minutes of arc, and each minute of arc is again divided by 60 seconds of arc, or arc-seconds.  So there are exactly 3600 arc-seconds in each one degree angle.
Typical measurements in astronomy... Jupiter's disk subtends about a 40 arc-second angle, the double star Albireo subtends 35 arc-seconds, and the Polaris double is separated by 19 seconds of arc.   The really close and tight double stars are typically only one and two arc-seconds apart,
(like the famous double double star Epsilon Lyrae)... and are very tough to cleanly split unless you have a very clear, steady sky. Like I said earlier, with the larger scopes, it's the atmosphere that is the limiting factor for sub arc-second resolution... and not the size of the telescope you are using.
But the Hubble telescope doesn't have to worry about an atmosphere limitation, so it can do sub arc-second resolution all the time... thus the high clarity (high resolution) of its pictures.
Clear Skies,
Tom