Views from the Very Large Telescope
ATLAS OF THE UNIVERSE
A Bok globule. This image
was obtained by the Antu
mirror of the VLT in 2001. It
shows a dark cloud, Barnard
68 (B68); this is one of the
Bok Globules, named for the
Dutch astronomer Bart J.
Bok, who first suggested
their existence. A Bok
Globule is the precursor of a
star. In time it collapses, the
interior temperature rises,
and when the temperature is
high enough the fledgling
star begins to shine. B68 is in
the pre-collapse stage, it is
410 light-years away, and its
size is around 12,500
astronomical units (2 million
million km or 1.2 million
miles), comparable with that
of the Sun’s Oort Cloud. The
temperature is 257 degrees
C; the total mass of the cloud
is about twice that of the
Sun. The pressure at the
boundary is 40,000 million
million times less than that
of the Earth’s air at sea level. The Butterfly Nebula:
NGC 6302 (Antu mirror, VLT,
1998). This is a planetary
nebula, only a few thousand
years old, 2000 light-years
away; its magnitude is 12.8,
and it lies between the stars
Lambda and Mu Scorpii. As
the central star of a binary
system aged, it threw off itsouter envelopes of gas in
a strong stellar wind. The
remaining stellar core is
so hot that it ionizes the
previously ejected gas,
making it glow. The nebula
will shine for a few thousand
years, after which the star
will fade and become a
white dwarf.M
uch the most powerful telescope now in existence is the
VLT or Very Large Telescope, at Cerro Paranal in the
Atacama Desert of Chile (latitude 24º38S, longitude
70º24W). To be precise the VLT consists of four 8-metre
mirrors (Antu, Kueyen, Melipal and Yepun) working
together – equivalent to a single 16-metre (630-inch) tele-
scope. Yepun, the last mirror, was completed in 2000. The
images obtainable are spectacular by any standards, and
surpass anything previously achieved.
Cerro Paranal is also the best possible observing site
on the Earth’s surface; the altitude is 2635 metres (8645
feet), rainfall is negligible and the percentage of clear
nights is very high. Moreover there is practically no prob-
lem with light pollution.E152- 191 UNIVERSE UK 2003mb 7/4/03 5:51 pm Page 190