Chp. 4 - Light and Telescopes

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

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 can't store data
  4. Poor

    5. resolution

    pupil - 1 arc min -> a dime a 60 m
    retina - 3 arc min
    the atmosphere - 1/2 arc sec -> a dime at 7 km

Refraction

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

Lens

- uses refraction to focus light

refracting

telescope - chromatic aeration

reflecting

telescope - spherical aeration

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 aeration

When buying a telescope

light gathering power (LGP)

then

resolution

are the most important features

LGP area of the mirror

a = r2 and is constant

diameter is 2r so we can compare diameters

( d1/ d2 )2

example
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 -> it's everywhere!

 Return to Main Astronomy Notes page