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)

Least Energy Orbit to Mars Sun Earth Mars Spacecraft Orbit Time to get to Mars   P 2 =a 3   a Earth = 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 , 6.7  Quiz #1 on Monday  Study hard!