Telescopes
Telescopes collect light.
–
Their ability to magnify is secondary (and misleading)
Telescopes
A telescopes light collecting ability is dictated by the
area of its collecting aperture (a main lens or mirror).
–
A 3-meter diameter telescope collects nearly 10 times as
much light as a 1-meter diameter telescope
Telescope Types
There are two fundamental types of telescope.
–
Refractors – use transparent lenses to bend the light to a focus.
–
Reflectors – use curved mirrors to reflect the light to a focus.
Telescope Types
In both type of telescopes the lens/mirror makes an image
of the sky that is either cast upon a detector or
photographic film or is inspected by an eyepiece.
Telescope Types
In both type of telescopes the lens/mirror makes an image
of the sky that is either cast upon a detector or
photographic film or is inspected by an eyepiece.
Reflectors vs. Refractors
Refractors can be great backyard telescopes, but all
large modern research telescopes are reflectors.
–
Huge lenses or mirrors will sag if not supported. A
transparent lens can only be held by the edge.
–
A mirror can be supported from behind and does not need
to be transparent or perfect on the inside like a lens
does.
Reflectors vs. Refractors
Refractors can be great backyard telescopes, but all
large modern research telescopes are reflectors.
–
A mirror can be supported from behind and does not need
to be transparent or perfect on the inside.
Telescope Precision
A giant telescope mirror must be manufactured with a
surface precision of 1/1000th the width of a human hair.
The mirror support structure must hold this precise
shape as the telescope points around the sky.
Telescope
Precision
The shape is polished
onto a slab of glass
The glass is coated with
a thin layer of
aluminum to make it
reflective.
Telescope Precision
All of the bulk of a telescope is necessary to get a few
grams of aluminum in the right shape and pointed at
the right spot on the sky.
Telescope Precision
All of the bulk of a telescope is necessary to get a few
grams of aluminum in the right shape and pointed at
the right spot on the sky.
UVa's Local Research Telescopes

31” and 40” telescopes on Fan Mountain 15 miles south
of Charlottesville.
Fan Mountain Infrared Camera


Telescopes are only as good as the instruments that
collect light attached to the back end.
This infrared camera was designed and fabricated from
scratch by UVa graduate and undergraduate students.
NGC1333
More Distant Facilities


The East Coast is not the best location for a telescope.
Apache Point Observatory, New Mexico - a remotely
operated 3.5 meter telescope
TripleSpec

An infrared high-resolution spectrograph for Apache
Point Observatory.
TripleSpec in Application: Uranian System
(Verbiscer and Skrutskie, UVa, Oct 17 UT)
Currently Uranus is located near ring plane crossing,
concentrating the ring flux in the spectrograph slit.
de Pater/Hammel (Keck)
Oct 17 UT
The satellite orbits are also on edge at this time
permitting the observation of planet, rings, and satellites
in one TripleSpec slit.
Below is the H and K band spectral orders obtained with the view at
left in the slit. The planetary atmospheric spectrum is spatially
resolved. High SNR spectra of Titania, Umbriel, Ariel, and Oberon
are obtained simultaneously. Auroral emission from molecular
hydrogen is visible in the K-band (inset). The exposure
time was 240s.
The Large Binocular Telescope
The Large Binocular Telescope
●
●
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Uva is also a partner in developing and operating the world's current
largest optical telescope.
The “LBT” is TWO 8.4-meter mirrors on a single mount.
Uva has developed an infrared imaging system for planet hunting on
this telescope.
The Large Binocular Telescope
●
●
●
UVa is also a partner in developing and operating the world's current
largest optical telescope.
The “LBT” is TWO 8.4-meter mirrors on a single mount.
UVa has developed the world's best infrared imaging system for
planet hunting, now operating on this telescope.
Resolving Power
In addition to collecting light, an astronomer is
interested in resolving fine detail.
Resolving Power
A telescope's resolving power is limited by
–
atmospheric “seeing” - the twinkling of the stars
–
diffraction - passing light through an aperture blurs the
image.
“Fixing” Atmospheric Seeing
With fast computers and flexible mirrors astronomers
can undo the blurring effects of the Earth's atmosphere.
Resolving Power
A telescope's resolving power is limited by
–
atmospheric “seeing” - the twinkling of the stars
–
diffraction - passing light through an aperture blurs the
image.
Working at long wavelengths (e.g. radio) requires a big
telescope.
Hubble produces sharper images with its ultraviolet
cameras than with its infrared cameras.
Resolving Power
A telescope operating at radio wavelengths must have
a huge aperture to achieve good resolution.
–
diffraction - passing light through an aperture blurs the
image.
Working at long wavelengths (e.g. radio) requires a big
telescope.
Hubble produces sharper images with its ultraviolet
cameras than with its infrared cameras.
Interferometry
Multiple small telescopes can be combined to achieve
the resolving power of a single giant mirror (but not the
light collecting ability).
Astronomy from Space
Working from the ground, astronomers must contend
with the Earth's atmosphere.
–
In addition to blurring the view due to seeing, the atmosphere
also strongly absorbs some types of electromagnetic radiation.
–
High mountaintops help, in some cases, but space provides the
ultimate solution.
Astronomy from Space
Working from the ground, astronomers must contend
with the Earth's atmosphere.
–
In addition to blurring the view due to seeing, the atmosphere
also strongly absorbs some types of electromagnetic radiation.
–
High mountaintops help, in some cases, but space provides the
ultimate solution.
To avoid the worst of
the atmosphere's
absorption, infrared
observations, for
example, must be
conducted from highaltitude aircraft or
from space
The “Great Observatories”
For the last two decades NASA and its international
partners have developed powerful space observatories
that span the electromagnetic spectrum.
Hubble Space
Telescope
(visible)
Spitzer (infrared)
Space Telescope
Compton Gamma-ray
Observatory
Chandra X-ray Observatory
The Spitzer
Space
Telecope,
launched in
2003,
provided
an infrared
view of the
universe.
Liquid
Helium
cooled the
telescope to
less than 10
degrees
above
absolute
zero to make
it sensitive
to the faint
infrared glow
of
astronomical
objects.
The Wide-Field Infrared Survey Explorer
“WISE” has mapped the
entire sky at infrared
wavelengths
–
3, 5, 12, and 23
micrometers to be
specific.
Solid hydrogen cooled the
detectors and telescope to
temperatures as low as 8
degrees above absolute zero.
WISE was launched from
Vandenberg Air Force Base
on a Delta-2 rocket on
December 14, 2009.
–
WISE is in a 500 km
high orbit that
keeps it continually
over the
sunrise/sunset line.