QUESTION:
Our teacher read to us where the Hubble has found
that earth's temperature is 20 degrees lower than
when the voyager spacecraft took the temperature in
1970? Can the Hubble be used to predict another ice
age in the future? Our class also read where some
islands are sinking due to the polar icecaps melting
can the Hubble help us determine if that is true?

ANSWER from Sanjay Limay on May 30, 1996:
I think the temperature change reported from HST observations was for Mars,
not the earth. HST has no capability to measure temperature changes directly
on earth (or any other planet for that matter) since it does not have the
appropriate instruments.  Even on Mars, the temperature change reported in
conjunction with the HST images obtained at different wavelengths was
actually determined from other ground based observations, and were
consistent with the relatively dust free atmosphere of Mars indicated by the
HST observations.

HST also cannot be aimed at the earth most of the time as the earth is too
bright for most instruments and in fact is out of focus.  In general the HST
cannot be aimed at an angle less than 45 degrees with the sun, moon and the
earth, to look at any object in the sky.  This why observations of Venus are
so rare from HST, and why Mercury cannot be observed from HST.

To learn more about the earth, and whether the ice caps are melting, and
whether some "islands are sinking" (think about it.  Can they really sink?
 To do so, they would have to be floating!), there are many earth orbiting
satellites that monitor the earth continuously.  These include the
geosynchronous and polar orbiting weather satellites from different nations
(US, India, Japan,  European countries, and Russia) as well as remote
sensing satellites (ERS-1 and 2, RADARSAT, JERS, TOPEX).  You can find out
about these earth observing satellites on the web.  If you need help, please
contact me.

Please verify with your teacher that I have "guessed" the planet correctly.