Download Observatories_handout - Department of Physics and Astronomy

PHY100 ─ ASTRONOMICAL OBSERVATORIES
Why do we need more than one type of telescope in order to observe space?
 The differing wavelengths of various energies create different instrumental
needs resulting in dissimilar detecting devices.
 Telescopes rely on the interaction between energy and matter. The atomic
matter that forms the telescope has to interpret the energy emitted from
astronomical objects. This energy is in the form of electromagnetic waves.
 Most of the universe is invisible to us because we only see the visible light
portion of the electromagnetic spectrum.
 When most people think of telescopes they think of visible light, or optical
telescopes.
Types of Optical Telescopes
 The refracting telescope uses lenses to form an image. The light is bent, or
refracted, causing parallel light waves to converge at a focal point, while
those that are not parallel converge at a focal plane. Most of the universe is
invisible to us because we only see the visible light portion of the
electromagnetic spectrum.
 The reflecting telescope uses an arrangement of mirrors to form an image.
This design allows for very large diameter objects to be observed. Reflecting
telescopes come in many design variations and use other optical elements
to improve image quality and place the image in a mechanically
advantageous position.
 Catadioptric telescopes have both lenses and mirrors. The combination
increases the effective focal length of the telescope and they can be made
into a more compact piece of equipment. For this reason, it is used mostly
for cameras and other light in weight technologies.
Refracting Telescope
 The first telescopes that were built were refractors.
 The main advantages of the refracting telescope are that it is not fragile and
rarely needs to be realigned; the inner part of it is sealed from the outside
and does not need to be cleaned frequently as a result.
 Main disadvantage is that all refractors suffer from an effect called chromatic
aberration (‘color deviation or distortion’) that produces a rainbow of colors
around the image. Physical disadvantage is that the glass lenses often have
imperfections, which can damage the image.
Reflecting Telescopes
 Reflecting telescopes fixed all of the problems of refracting telescopes by
using mirrors.
 There are two mirrors, one curved that is at the top of the telescope and a
smaller one that sends light out of the side of the telescope tube so the
image can be viewed without blocking the incoming light. This mirror
scatters the light, which degrades the image to a certain degree.
 The disadvantages are relatively minor, most notably that the optics of
this telescope can fall out of alignment quite easily, and the reflector’s
tube is open at one end, unlike the refractor, so it needs frequent
cleaning.
Catadioptric Telescopes
 The main advantages of Catadioptic telescopes are that they employ
spherical surfaces that are easier to manufacture. By combining a moving
primary mirror with a cassegrain configuration allow for large movements in
the focal plane to accommodate cameras and CCDs.
 A disadvantage to this design is that the secondary mirror blocks a portion of
the light entering the tube.
Optical Telescopes
 The difference between optical telescopes is the way in which they gather
light through their “objective”, the part of the telescope that gathers light.
Radio Telescopes
 Radio telescopes are directional radio antennas.
 Dishes composed of conductive wire mesh whose openings are smaller than
the wavelength being observed.
 Most radio telescopes need to be large in order to accommodate radio's
longer wavelengths and lower energies.
 Radio telescopes dishes are made of either metal or wire mesh; either
design still serves the same purpose. Radio waves are large, and as a result
radio telescopes tend to be quite large too.
X-ray and Gamma-ray Telescopes
 This type of telescope utilizes “glancing mirrors” and heavy metals which are
able to reflect the rays a few degrees.
 Gamma-ray telescopes use coded aperture masks. The pattern of the
shadow that is created by the mask can be reconstructed to form an image.
 These telescopes are usually located on satellites orbiting Earth since the
Earth’s atmosphere is opaque to this part of the electromagnetic spectrum.
Purpose of Satellites in Space
 Collect data, photos and other info from Earth and the many things that
surround it.
 Study outer space and earth’s atmosphere, track weather patterns and
acquire intelligence.
Ground Based Observatories
 For optical telescopes, most ground-based observatories are located far
from major centers of population to avoid the effects of light pollution.
 The ideal locations for modern observatories are sites that have dark skies,
a large percentage of clear nights per year, and dry air.
 High elevations are a very important condition. At high elevations, the
Earth’s atmosphere is thinner, which minimizes the effect of atmospheric
turbulence and allows better astronomical “seeing.”
Radio Observatories
 Radio observatories are located far from major centers of population to
avoid electromagnetic interference (EMI) from radio, television, radar, and
other EMI emitting devices.
 Radio observatories will be placed in valleys to further shield them from EMI.
 Some of the major radio observatories are at Socorro, in New Mexico,
Jodrell Bank in the UK, Arecibo, Puerto Rico and Parkes in New South
Wales, Australia.
Satellites Past, Present and Future
PAST
 Sputnik was the first satellite to be launched into orbit around Earth.
 Launched in 1957 by the Soviet Union
 It was a small silver ball, less than 1 foot across with antennas that sent out
a “beep-beep-beep,” signaling it was the first satellite to make it successfully
into space.
PRESENT
 The Hubble Space Telescope (HST), launched in 1990 and still in space, is
a large, space based observatory.
 Has revolutionized astronomy by providing unprecedented deep and clear
views of the universe, ranging from our own solar system to ancient, faraway
galaxies formed 13.7 years ago after the Big Bang. It has also been
instrumental in detecting black holes.
 Hubble orbits earth every 96 minutes, 575 km above Earth’s surface.
FUTURE
 The Herschel Space Observatory
 Space-based telescope that will study the Universe by the light of the farinfrared and sub millimeter portions of the spectrum
 It is expected to reveal new information about the earliest, most distant
stars and galaxies, as well as those closer to home in space and time. It
will also take a unique look at our own solar system. It is scheduled to be
launched in early 2009.
 The Gravity Recovery and Interior Laboratory, or Grail will fly twin
spacecraft in tandem orbits around the moon for three months to
measure its gravity field in unprecedented detail. It will be launched in
2011.
 Kepler is a space borne telescope designed to survey distant stars to
determine the prevalence of Earthlike planets. Scheduled to launch in
2009.
 Juno will conduct an in-depth study of the giant gas planet Jupiter
 A spacecraft will enter polar orbit around the planet to investigate the
existence of an ice-rock core; determine the amount of global water and
ammonia present in the atmosphere. It will be launched in august 2011.
 The Nuclear Spectroscopic Telescope Array, or NuSTAR is a
pathfinder mission that will study the sky through high energy X-rays. It
will be launched in 2011
 The “Pico” satellite is currently being designed and built at the University
of Florida with the intent of creating a satellite that is small, inexpensive
and easily mass-produced.
 The Next Generation Space Telescope (NGST) is NASA’s next step in
satellites. Set to be launched in 2013, the James Webb Space telescope
is a large, infrared-optimized space telescope that is expected to find the
first galaxies formed in the early universe.
Possible Exam Questions
- Why do we have different types of telescopes?
- What are the types of optical telescopes? Briefly explain how they work.
- Why are most observatories located at high elevations?