Telescopes and Spacecraft

Astronomy 311Professor Lee

CarknerLecture 7

If it is low tide where you are standing right now, how many total places on Earth are at low tide right now? How many total places on Earth are at high tide right now?a) 1 and 0b) 1 and 1c) 1 and 2d) 2 and 2e) 4 and 4

Which of the following would the Earth’s magnetic field have no effect on?

a) An ionb) An electronc) A neutral oxygen atomd) A negative hydrogen atome) A positive helium atom

How Do Telescopes Work?

Telescopes: Focus light to produce an image

Light gathering ability (not magnification) is the most important attribute 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

A curved mirror can be used to gather and focus the light instead (reflecting telescope) 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

Spacecraft

Types of spaces probes: Fly-by -- collects data as it passes by

Example:

Orbiter -- circle planet and study for a long time Example:

Lander -- land on the planet and take samples Example:

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)

Least Energy Orbit to Mars

Sun

Earth

Mars

Spacecraft Orbit

Time to get to Mars P2=a3

aEarth = 1 AU

aMars =1.5 AU Time = =

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

We see different wavelengths of visible light as colors red -- blue --

We want to view all types of electromagnetic radiation

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)

some penetrates atmosphere, but to observe all UV

wavelengths need to go into space X-ray

all X-rays blocked by atmosphere

Gamma Ray 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)