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:   find pieces of solar system that have visited us (meteorite)

How Do Telescopes Work?  Telescopes:     Light gathering ability (not magnification) is the most important attribute of a telescope  telescopes make faint things brighter

Lenses  If you point an empty tube at an object, you may be gathering lots of light, but it doesn’t get to your eye   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  mag.= f.l. objective / f.l. eyepiece 

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  A curved mirror (the primary mirror) reflects light so that it is focused  Problem: The focal point is between the mirror and the sky   Cassegrain Telescope --

Cassegrain Reflecting Telescope

Path of Light  Light beams enter from infinity and are initially parallel   The eyepieces then magnifies the point image by taking the divergent rays from the focal and making them parallel again 

5 meter Hale Telescope at Mount Palomar

The Hobby-Eberly Telescope

What Can a Telescope Do?  Imaging --  Photometry –  Spectroscopy --  A spectrum is the amount of light at each wavelength.  The shape of the spectrum tells you about the temperature, composition and motions of the object

Types of Detectors  Eye -- limited ability to do photometry or spectroscopy, data is difficult to analyze (must write down what you see)  Photographic plate --  Charge Coupled Device (CCD) -- more sensitive and easier to use than a plate, allows you to store and reduce data electronically 

Telescope Misconceptions  Magnification is the most important property of a telescope   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  The wavelength relates to energy  long wavelength --  short wavelength --  We see different wavelengths of visible light as colors  

The Electromagnetic Spectrum

Observing at Different Wavelengths  Planets, stars and galaxies produce radiation at many different wavelengths in many different ways   Many types of light don’t penetrate the Earth’s atmosphere and need to be observed from orbit 

Telescope Taxonomy  Radio and Millimeter -- penetrates atmosphere and everything else   Example:  Infrared (IR) -- we feel as heat   Example:  Optical -- what our eyes can see   Example --

More Telescope Taxonomy  Ultraviolet (UV) -- high energy radiation, causes sunburn   Example --  X-ray -- very high energy   Example --  Gamma Ray -- the highest energy   Example --

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:  Orbiter --  Example:  Lander --  Example:

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  Once the spacecraft is out of the Earth’s gravity well, a little nudge with the thrusters will send it on its way   Easiest way to get to a planet is a least energy orbit 

Least Energy Orbit to Mars Sun Earth Mars Spacecraft Orbit Time to get to Mars     a Earth = 1 AU  a Mars =1.5 AU 

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)