STARS AND GALAXIES
Part I: A Trip Through the Universe
“Our Transportation”
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What do you see when you look up
at the sky on a clear night?
The night sky at ESO's La Silla Observatory in Chile
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What might appear different if you were
to use a telescope?
Four Faces of Mars photographed
by the Hubble Space Telescope
Credit: S. Lee (U. Colorado) et al.,
WFPC2, HST, NASA
Globular cluster Messier 10 seen
here in an image from the 3
NASA/ESA Hubble Space Telescope
TELESCOPES
• Unlike a microscope whose function is to
magnify small objects, when looking at the
stars, magnification is not very important.
No matter how much you magnify them
they still look like points of light.
• Telescopes are built to collect light. They
allow scientists to examine objects that are
too dim or too far away to see unaided.
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TYPES OF TELESCOPES
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REFRACTING TELESCOPE
• Uses a series of lenses
to focus visible light
• Limited by how large
lenses can be made
FYI: The largest is the 40-inch
Yerkes telescope, built in 1895
in Wisconsin (40 inch lens in a
sixty-foot long telescope)
Pictured right – can you spot
the famous scientist in the
picture?
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REFLECTING TELESCOPES
• A series of mirrors is used to
collect and focus light
• Images are captured by
cameras (now replaced by
newer technology that works
with computers); long
exposures allow objects too
dim to see with our eyes to
be “seen.”
• Usually built atop mountains
to reduce atmospheric
interference
FYI: Largest is the 200” Hale
telescope on Mt. Palomar in CA
100” Hooker Telescope on Mt. Wilson
in CA; used by Edwin Hubble to
discover the existence of galaxies
other than the Milky Way
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REFLECTING TELESCOPES
FYI: Until the late 20th century, just like refracting
telescopes, the size of reflecting telescopes was
limited by how big a mirror could be made before it
would distort itself under its own weight.
Scientists developed two solutions to this problem.
They developed a new way to make very large
mirrors (6-8+ meters in diameter) and a way to
combine multiple mirrors that work together as one.
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MULTIPLE MIRROR REFLECTING TELESCOPES
• Use multiple mirrors
that act together as a
much large mirror
• The Keck telescopes
on Mauna Kea (a
dormant volcano) in
Hawaii are two
telescopes, each with
36 mirrors that make
a 400” mirror.
Aerial view of Keck I and
Keck II Observatories
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ELECTROMAGNETIC SPECTRUM –
LIGHT WAVES
• Energy travels through space in the form of waves.
• The shorter the wavelength the higher the amount
of energy.
• All electromagnetic waves travel at the same speed
(~300,000km/s or 186,000 mi/s)
• Visible light is only a small portion of the EM
spectrum.
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THE SPECTROSCOPE
• An instrument used with a visible light
telescope to separate the visible light from
individual stars into its component colors
• The spectrum of a star can tell a scientist how
hot a star is. Bluer stars are hotter than
redder stars. Why?
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THE SPECTROSCOPE
• The spectrum of a star
also tells us the
composition of a star
(the elements it is
made of.)
• The black lines in the
spectrum are
absorption lines, and
they can be used to
determine composition
of the star.
Spectrum of a star. Graph of spectral
luminosity versus wavelength.
Later we will see that the spectrum of a star can also be used to
determine how far away from Earth it is.
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RADIO TELESCOPES
– collect radio
waves and use
them to produce
an image
FYI: The Very Large Array, one of
the world's premier astronomical
radio observatories, consists of
27 radio antennas in a Y-shaped
configuration on the Plains of San
Agustin fifty miles west of
Socorro, New Mexico.
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INFRARED TELESCOPES
• Detect low energy
light from objects
that are normally
hidden by dust clouds
• May be land-based or
in space.
The IRTF is NASA’s 3.0 meter
telescope, optimized for infrared
observations, and located at the
summit of Mauna Kea, Hawai`i.
Spitzer Infrared Space Telescope
Launched 2003
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ULTRAVIOLET TELESCOPES
Generally must
be placed above
the atmosphere
to be effective,
as much UV light
is blocked by the
Earth’s
atmosphere
The Galaxy Evolution Explorer
(GALEX) is an orbiting space
telescope observing galaxies in
ultraviolet light
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X-RAY TELESCOPES
• Must be above the
atmosphere as X-rays
from space do not pass
through the
atmosphere
• Use special reflectors
to focus X-rays and
produce an image
• The first X-ray
telescopes were used
to observe the sun. FYI: The Chandra X-ray Observatory
was launched in 1999. It orbits the
Earth 200 times higher than Hubble.
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GAMMA RAY TELESCOPES
• Gamma rays are very
high energy light rays
and scientists have
developed technology to
detect and image gamma
radiation from space
• Must be above the
atmosphere to detect
• Certain cosmic events
radiate large amounts of
gamma rays
Compton Gamma Ray Observatory
Used from 1991 - 2000
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THE HUBBLE TELESCOPE
• Named after Edwin Hubble
• Launched in 1990 and
repaired/upgraded by
astronauts since then
• A reflecting telescope designed
to detect light in the infrared,
visible, and ultraviolet light
ranges without distortion
caused by the atmosphere
• Has greatly increased our
knowledge of distant galaxies
and the universe
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PICTURES FROM HUBBLE
Dusty Spiral Galaxy
Butterfly Nebula
HST NGC 6751 Aquilla Nebula
Cat’s Eye Nebula
Two Colliding Spiral Galaxies
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ONE VIEW THROUGH 4 TELESCOPES
Crab Nebula in different wavelengths. Image from NASA.
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