Astronomy 1
Fall 1998

October 14 Lecture

Optics, Telescopes and Astronomical Instruments

Text Chapters (Chaisson) = #5 (Read, Look at Figures and READ the CAPTIONS)
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NOTICES
- 1 Hour Test - Next Wednesday: October 21 
   In Class Test (Chapters 1-5, Text part of chapter 5 only) plus time and coordinates
- Halifax RASC meeting - Friday Oct 16, 8pm NS Museum - Oceans of Venus 
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Astronomical Event:

Monday 12 - Last Quarter Moon
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HOMEWORK: Due Next Monday: (NOTE DIFFERENT DUE DATE)
Chapter 3
Problems #4, 6, 10
Chapter 4
Problems #2, 5, 8, 10
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LECTURE  
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SEE Optics Page
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Resolving Power of all types of radiation telescopes (not just optical)
	a (radians) = 1.2 l/D 		1 radian = 206,300"arc
	a ("arc) = 0.25  l(mm)/D(m)
Microwaves l = 1mm = 1000 mm
How big a radio telescope does it have to be to resolve 1"arc?
D(m) = 0.25 l(mm)/a ("arc) = 0.25 (1000 )/1 = 250 m

Types of Telescope Designs
	-Refractor 
	-Newtonian Reflector
	-Cassegrain
	-Schmidt
	-Schmidt-Cassegrain
	-Maksutov
Mounts
	-Equatorial
	-Alt-Azimuth (New computer controlled large telescopes)
		Smithsonian Astrophysical Observatory on Mt Hopkins
		Mulitple-Mirror Telescope
		also -- Keck telescopes on Mauna Kea (Hawaii)

READ THE TEXT WHICH HAS GOOD DISCUSSION OF TELESCOPES
	active optics, multiple mirror telescope, adaptive optics, interferometers

Detectors:
(Visible, Near UV, Near IR)(300nm - 1000nm)
1. The Eye (see also Oct 7 Lecture)
	Convenient - insensitive - Not Quantitative
	Resolution 1' arc at fovea centralis (cones)
		Colored vision less sensitive and in the cones by a factor of 100
	Resolution away in the rods = 5-10' arc		
	Only B&W at low light levels (peak at 500 nm) Rhodopsin in rods
		(Dark adaptaton 20-30 minutes)
		1-10 photons required to trigger detection
	Use averted vision because cones not at center of eye (rods are)
2. Magnitude Scales (SEE optics / magnitudes
		logrithmic response to light energy
		m2 - m1 ~ log10(B1/B2)
		m2 - m1 = 5  ---> B1/B2 = 100
		so m2 - m1 = 2.5 log10(B1/B2)
			m2 - m1= 1 corresponds to B1/B2 = 2.51
	table:
		m2 - m1		B1/B2
		0.1		1.096
		0.2		1.202
		0.3		1.318
		0.5		1.585
		0.7		1.905
		0.8		2.089
		1.0		2.511
		2.0		2.511 x 2.511 = 6.31
		3.0		(2.511)3 = 15.9
		4.0		(2.511)4 = 39.8
		5.0		100
	example 1:
		Rigel (b Orionis)= 0.12 m
		d Orionis = 2.23
	find the ratio in brightness 
		magnitude difference = 2.23 - 0.12 = 2.11 ~ 2.1
	2 magnitudes = ratio of 6.31
	0.1 magnitudes = ratio of 1.096
 		So ratio = 6.31 x 1.096 = 6.9

	example 2:
		Ratio of brightness measured by photometer = 1256
		what is the difference in the magnitudes?
	1256 = 100 x 12.56 = 100 x 6.31 x 1.99
		100 --> 5 mag
		6.31 --> 2 mag
		1.99 --> 0.75 mag
	Dm = 7.75

	example 3:
		An open cluster is made of 30 13th magnitude stars
		What is the total magnitude of the cluster.
			Cluster is 30 times brighter that one star.
		30 = 15.9 x 1.89 
		15.9 = 3 mag
		1.89 = 0.7 mag
	So the cluster has the magnitude of 13 - 3 - 0.7 = 9.3 m
	
	NOTE: Brighter stars have a smaller magnitude!

2. Photography
	large sky coverage - moderate sensitivity but non-linear response
	difficult to analyze quantitatively
	Difference emulsion sensitivities (blue, red)
3. Photometers (photomultipliers, photoelectrics)
	Quantitative, sensitive, linear response 
	Photon counting
	No Image
4. CCD (Charged Coupled Devices)
	Quantitative,  small area coverage, sensitive, linear response
	Image, Computer data storage and analysis
5. Spectrometers
	Gratings and Prisms

Other Telescopes:
Radio and Microwave
	No imaging - single detector
	Must scan to produce an "image" = contour map of intensity
	Single - Steerable (Penticton - Green Bank)	(Large area for sensitivity)
		Fixed (Arecibo)	(Much Larger area but limited pointing)
	Interferometers		(Increase resolution)
	Very Large Base Line or Very Large Array Interferometers
Example: wavelength = 1 m 
              baseline = 1000 km = 106 m
	a" = 206,300 (1/106) = 0.2 " arc
at wavelength = 1cm , a" = 0.002"arc using the VLBI
X-ray and Gamma Ray
	Difficult to make a refractive or reflective surface. 
X-ray 
	Use grazing angles to get reflectance and focusing
Gamma rays 
	Tracks in Photographic Plates
	Counters

Satellite Observatories (above the atmosphere to detect UV, X-ray, Gamma Rays
Hubble Space Telescope (See Interlude 5-1) 2.4m optical 
	In orbit 1990, repair 1993, 
	http://www.stsci.edu
IRAS (Infrared Astronomical Satellite) 1983 (no longer working but produced important survey)
IUE (International Ultraviolet Explorer) 1978-
HEAO (High Energy Astronomical Observatories)  - Einstein Observatory (1979)
ROSAT (Roentgen Satellite) 1990
GRO (Gamma Ray Observatory) Compton Observatory 1991

Spectrum Photos in the Text

RIVUXG
(Radio - Infrared - Visible - Ultraviolet - Xray - Gamma)
See Table 5-1 READ