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