ASTR-1010ASTR-1010Planetary AstronomyPlanetary Astronomy

Day - 18

AnnouncementsAnnouncements

Smartworks Chapters 4: Due Monday, March 1.

Smartworks Chapter 5 is also posted

Exam 2 will cover chapters 3, 4, & 5

-Target Wednesday, March 3

ClassAction StuffClassAction Stuff

• Splash page questions

Telescopes & Instruments Telescopes & Instruments

TelescopesTelescopes

Telescopes have three functions:

1. Gather light

LGP ∝ Area = πR22. Resolve objectsΘ = 2.06 X 105 (λ/D)3. Magnify EXTENDED objects

The light gathering power is The light gathering power is proportional to the areaproportional to the area

Properties of light: RefractionProperties of light: Refraction

The Speed of Light is less in glass than in vacuum

Refraction through a plane of glass Refraction through a plane of glass only shifts the light, a lens with curved only shifts the light, a lens with curved

surfaces focuses the lightsurfaces focuses the light

The The refractingrefracting telescope uses telescope uses two lensestwo lenses

Refractors suffer from Refractors suffer from Chromatic AberrationChromatic Aberration

Chromatic Aberration distorts Chromatic Aberration distorts colorscolors

Rainbows appear around bright white objects

ClassAction StuffClassAction Stuff

• Simple Telescope

• Snell’s Law

• Splash page questions

Correcting for Chromatic Correcting for Chromatic aberration can be aberration can be expensiveexpensive

Large refractors Large refractors can be very long can be very long and bulky. The and bulky. The

largest has a 40” largest has a 40” diameterdiameter

The Yerkes 40” The Yerkes 40” moves the floor to moves the floor to

view at low angles view at low angles

Cheaper WayCheaper WayMirrors Mirrors

Reflection is Reflection is the bouncing the bouncing of light off a of light off a

surfacesurface

A concave mirror focuses lightA concave mirror focuses light

There are There are several several types of types of reflecting reflecting

telescopestelescopes

Spherical mirrors suffer from Spherical mirrors suffer from Spherical AberrationSpherical Aberration

Spherical Spherical aberration can aberration can

be eliminated by be eliminated by a parabolic a parabolic shape or a shape or a

corrector platecorrector plate

The Largest Optical TelescopesThe Largest Optical TelescopesKeck I and IIKeck I and II

The 10 meter Keck MirrorThe 10 meter Keck Mirror

The Hobby-Eberly TelescopeThe Hobby-Eberly Telescope

Coming “soon”Coming “soon”The 30m TelescopeThe 30m Telescope

The resolution of a telescope The resolution of a telescope depends on its size and the depends on its size and the

wavelength of the lightwavelength of the light

The atmosphere limits the The atmosphere limits the resolving power of a ground-resolving power of a ground-

based telescopebased telescope

Differences in the temperature Differences in the temperature and density of small portions and density of small portions of Earth’s atmosphere cause of Earth’s atmosphere cause passing starlight to quickly passing starlight to quickly

change direction, making stars change direction, making stars appear to twinkle.appear to twinkle.

Earth’s atmosphere hinders astronomical researchEarth’s atmosphere hinders astronomical research

Image of stars taken with a telescope on the Earth’s surface

Same picture taken with Hubble Space Telescope high above Earth’s blurring atmosphere