Telescopes and Spacecraft Astronomy 311 Professor Lee Carkner Lecture 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 0 b)1 and 1 c)1 and 2 d)2 and 2 e)4 and 4

Which of the following would the Earth’s magnetic field have no effect on? a)An ion b)An electron c)A neutral oxygen atom d)A negative hydrogen atom e)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 

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

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   P 2 =a 3   a Earth = 1 AU  a Mars =1.5 AU  Time = =

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:

Next Time  Read , 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)