Transcript Telescopes and Spacecraft

Telescopes and Spacecraft
Astronomy 311
Professor Lee Carkner
Lecture 7
How Do Telescopes Work?
Telescopes:

Focus light to produce an image

Quality and light gathering ability (not
magnification) are the most important
attributes of a telescope
telescopes make faint things brighter
Lenses

Need a lens
Lenses bend light (refraction) and focus
all of the light incident on the front to a
point (focus) a certain distance behind
the lens (focal length)
Lenses and Refraction
Refracting Telescope

This produces a refracting telescope

 mag.= f.l. objective / f.l. eyepiece
in practice the magnification you can achieve is
limited by the blurring effects of the Earth’s
atmosphere
Refracting Telescope
Refractors and Reflectors

Makes them
hard to make flawless
heavy and hard to support

large mirrors are easier to make and support
Reflecting Telescopes

Problem: The focal point is between
the mirror and the sky

Cassegrain Telescope -- secondary
reflects light through a hole in the
primary, most common type of large
telescope
Cassegrain Reflecting
Telescope
Telescope Misconceptions
Magnification is the most important
property of a telescope
image quality and light gathering ability (size)
are what is important
Astronomers peer through an eyepiece

Telescopes stick out of the dome

Telescopes fold up like a giant pirate’s
spyglass

Least Energy Orbit

Once in space they coast to the planets,
following Kepler’s Laws

An orbit that intersects the Earth’s orbit at
one point and the other planet’s orbit at
another point (on the opposite side of the
Sun)
Mars
Sun
Earth
Spacecraft
Orbit
Least Energy Orbit to Mars
The Electromagnetic
Spectrum
Every photon (light particle) has a
wavelength which places it in the
electromagnetic spectrum

long wavelength -- low energy
short wavelength -- high energy

red -- long wavelength
blue -- short wavelength

So we can explore all physical processes
The Electromagnetic Spectrum
Telescope Taxonomy
Radio and Millimeter

penetrates atmosphere and everything else
Infrared (IR)

some penetrates atmosphere, but to observe all IR
wavelengths need to go into space
Optical

it helps to get above atmosphere (no blurring =
sharper images)
More Telescope Taxonomy
Ultraviolet (UV)
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some penetrates atmosphere, but to observe all UV
wavelengths need to go into space
X-ray
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all X-rays blocked by atmosphere
Gamma Ray
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all Gamma rays blocked by atmosphere
Next Time
Read 15.1-15.4 , 6.7
Quiz #1 on Monday
Study hard!
Summary
Refracting Telescopes use a lens to
bend light to a focus
Reflecting Telescopes use a mirror to
reflect light to a focus
Most large research telescopes are
reflectors
Astronomers today record and analyze
data digitally
Summary
To observe the entire electromagnetic
spectrum you need many different
types of telescopes, some of them in
space
Spacecraft have allowed close up study
of the planets
Spacecraft reach their destinations by
using the gravity of the Sun (or sometimes
planets)