Telescopes and Spacecraft

Astronomy 311Professor Lee

CarknerLecture 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)

Least Energy Orbit to Mars

Sun

Earth

Mars

Spacecraft Orbit

Time to get to Mars P2=a3

aEarth = 1 AU Time = =

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!