Sky and Telescope - June 2015 - 21

How HUBBLE Changed
the Face of Astronomy
Govert Schilling

The ﬁrst of the "Great Observatory" space telescopes transformed
what astronomers knew - and didn't know - about the universe.

Until some 50 years ago, we basically didn't know our
solar system neighbors. The 200-inch Hale Telescope at
Palomar Mountain had provided us with some blurry
photos that hardly beat the view through a small amateur
telescope. Only with the advent of space exploration did we
start to discover intricate details on the Martian surface,
in Jupiter's cloud deck, and in the ring system of Saturn.

2. Nurseries Unveiled
One of the ﬁrst major science results from the Hubble
Space Telescope was the discovery of protoplanetary disks
(or proplyds for short) in M42, the Orion Nebula. Until
then, nobody really knew how unique - or how run-ofthe-mill - our own solar system might be. Ten years

H. HAMMEL / MIT / NASA

1. Solar System Surveillance

Hubble routinely takes high-resolution images of the
other solar system planets. It had a front-row seat when
Comet Shoemaker-Levy 9 slammed into Jupiter's atmosphere back in 1994. Ultraviolet observations - impossible from the ground - revealed auroras on Jupiter
and Saturn, as well as the breakup products of cometary
molecules. In addition, Hubble has discovered two new
moons of Uranus, one of Neptune, and four of Pluto, and
it found two distant Kuiper Belt objects that may serve as
goals for NASA's New Horizons probe after it ﬂies past
Pluto in mid-July.
Today, amateur astronomers using image-stacking
technology are also achieving incredible results in solar
system observations, as are professionals using adaptive
optics on large ground-based telescopes. Still, it's hard
to match Hubble's high-resolution vigilance over our
cosmic backyard.

NASA / ESA / J. CLARKE (BOSTON UNIV.) / Z. LEVAY (STSCI)

Many of today's astronomers were still in elementary
school when the Space Shuttle Discovery carried the
Hubble Space Telescope into orbit 25 years ago. Some
weren't even born yet. To them, Hubble has always been
around. Indeed, we've all grown familiar with the pretty
pictures and revolutionary results of the most successful
telescope in the history of astronomy. Even for veteran
researchers, it's hard to remember how diﬀerent the science of the universe looked before 1990.
It's also hard to remember that back then, many scientists were pretty skeptical about the space telescope, which
traces its origin back to a 1946 (!) proposal by astronomer
Lyman Spitzer (1914-1997). Over the years, Hubble experienced huge delays and cost overruns - some $2 billion
in 1990 dollars had been spent by the time it ﬁnally left
the launch pad, seven years overdue. Even worse, images
revealed a small but fatal ﬂaw in the 2.4-meter primary
mirror soon after launch; it took until December 1993 for
shuttle astronauts to install corrective optics.
But ever since, the Hubble Space Telescope has been a
magniﬁcent success story. The goals of its three original
Key Projects - measuring the expansion rate of the universe, using distant Cepheids to probe the intergalactic
medium, and carrying out a statistical survey of remote
galaxies by taking pictures of random ﬁelds of view -
were fully achieved and even surpassed. From planets
to supermassive black holes, Hubble has revolutionized
every single ﬁeld in astronomy.
To celebrate the space telescope's 25th anniversary,
let's take a look at seven ways in which Hubble turned
the tables in our knowledge of the universe.

Left: This visible and ultraviolet composite image reveals an
auroral oval on Saturn, where auroras can last for days. Right:
Fragments from Comet Shoemaker-Levy 9 left impact marks in
Jupiter's atmosphere in 1994, wowing astronomers.

Sk yandTelescope.com June 2015

http://www.SkyandTelescope.com

Sky and Telescope - June 2015

Table of Contents for the Digital Edition of Sky and Telescope - June 2015