Chp. 3 - Light and Telescopes

Light - separate HANDOUT

Refraction - the bending of light (EM rad) as it changes medium

What is a telescope?
An instrument that detects and collects EM radiation.

Lens - uses refraction to focus light
refracting telescope - chromatic aberration
reflecting telescope - spherical aberration

Optical Astronomy -> magnification & resolution

resolution - the ability to distinguish finer details and/or to distinguish to adjacent objects

Our eyes:
1. see only in the visible
2. limited aperture -> pupils (8mm - young/5mm - old)
3. Time - eyes ->30x/sec, so we canít store data
4. Poor resolution
pupil - 1 arc min -> a dime a 60 m
retina - 3 arc min

the atmosphere (.2) - .5 arc sec -> a dime at 7 km

Active optics - adjusts the mirror position by moving the mount
Adaptive optics - reshapes the mirror

Hubble Space Telescope (HST)

.1 arc sec - no atm limitation, only mirror size
can see in UV and IR
images concentrated w/ nice black background the problem -> spherical aberration

Radio Astronomy - slide show

Arecibo - world's largest radio telescope

When buying a telescope light gathering power (LGP) then resolution are the most important features
LGP µ area of the mirror
a = 1 r2 and 1 is a constant
diameter is 2r so we can compare diameter
( d1/ d2 )2

Magnification - number of times an objects angular size is enlarged
this is good for extended objects - galaxies, nebula, etc vs. point objects - stars, planets
mag = focal length / eyepiece 100cm/40mm -> 100cm/4cm = 25x

incr. mag you decr. field of view

Talking the Talk
(how to impress your friends and relatives)

Seeing - steadiness of the atm

transparency - how clear the sky is

light pollution -> itís everywhere! Slide show

Chp. 3 - Light and telescopes # of 4