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Telescopes and Spacecraft
Astronomy 311
Professor Lee Carkner
Lecture 7
How Do We Learn About The
Solar System?
View from Earth:


View remotely:

Other methods:
visit in person (Moon only)
find pieces of solar system that have
visited us (meteorite)
How Do Telescopes Work?
Telescopes:

Focus light to produce an image

Light gathering ability (not
magnification) is the most important
attribute of a telescope

Lenses


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
If you put a second lens (eyepiece) behind the
first lens(objective), you can magnify the
image

Magnification is equal to the ratio of the focal
lengths

in practice the magnification you can achieve is
limited by the blurring effects of the Earth’s
atmosphere
Refracting Telescope
Giant Refractor at Yerkes
Observatory
Refractors and Reflectors
It is hard to make large refracting
telescopes

A curved mirror can be used to gather
and focus the light instead (reflecting
telescope)

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
The Hobby-Eberly Telescope
Types of Detectors
Eye --
Photographic plate -Charge Coupled Device (CCD) -- more
sensitive and easier to use than a plate, allows
you to store and reduce data electronically
Today, light is moved around with fiber optic
cables and data is moved electronically
The Electromagnetic
Spectrum
Every photon (light particle) has a
wavelength which places it in the
electromagnetic spectrum
The wavelength relates to energy


We see different wavelengths of visible light
as colors


We want to view all types of electromagnetic
radiation

The Electromagnetic Spectrum
Telescope Taxonomy
Radio and Millimeter -- penetrates atmosphere
and everything else

Example: The VLA (Very Large Array)
Infrared (IR) -- we feel as heat

Example: IRAS (Infrared Astronomical Satellite)
Optical -- what our eyes can see

Example -- Hubble Space Telescope
More Telescope Taxonomy
Ultraviolet (UV) -- high energy radiation,
causes sunburn

Example -- IUE (International Ultraviolet Explorer)
X-ray -- very high energy

Example -- Chandra X-ray Observatory
Gamma Ray -- the highest energy

Example -- Compton Gamma Ray Observatory
The VLA
Hubble Space Telescope
Spacecraft
Since the 1960’s we have sent probes to
study the planets close up
Types of spaces probes:
Fly-by -Example: Voyagers I and II
Orbiter -Example: Mars Global Surveyor
Lander -Example: Mars Pathfinder
Getting to The Planets
Spacecraft don’t zoom around the Solar
System like in science fiction

Use small thrusters to maneuver
(remember Newton’s First Law -- Inertia)

Least Energy Orbit

After that it follows 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
Time to get to Mars
Sun
Earth
Spacecraft
Orbit

P2=a3

aEarth = 1 AU

Time =
=
Least Energy Orbit to Mars
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)
Next Time
Read 15.1-15.4, 6.7
Quiz #1 on Monday
Study hard!