1. Announcements
No class next week. I will be returning from Kitt Peak late Thursday so I won’t be back in time
Homework: Chapter 8 # 1, 2 & 4
Lab to do over the next two weeks: SDSS Advanced Projects: Hertzsprung-Russell Diagram

2. Light Detectors

3. Early astronomers were great sketch artists
Lord Rossi drawing of a spiral galaxy
Donati drawings of the head of a comet
Carrington’s drawings of a solar flare

4. The human eye is a remarkable instrument
The Cilary muscles can deform the lens, changing its focal length to adapt for nearby or distant objects

5. The eye’s photo detectors are called rods and cones

6. The cones are concentrated in the center of the retina while the rods are spread out

7. The rods are more sensitive than the cones

8. It takes some time for the eye to adapt to the dark

9. Photography came into use in the late 1800’s
Henry Draper was one of the first to use photographic plates for astrophotography

10. Techniques were developed to measure brightness on photographic plates
Plate densitometers would measure the density of exposed photographic grains to determine brightness

11. Photoelectric photometers provided an easier means of determining brightness

12. The most common detector was a photomultiplier tube

13. The SSP-3 Photoelectric Photometer is still available
The readout must be calibrated for absolute photometry or compared to a comparison star’s readout of differential photometry.

14. Modern solid state detectors eventually replaced photomultiplier tube
Photodiode detectors are much smaller, more sensitive and much more energy efficient

15. Image Intensifiers give real-time light amplification
The intensified image is usually a monochrome image

16. There are more military uses for image intensifiers than astronomical ones

17. Today, almost everyone uses CCD’s for photometry

18. The CCD is a simple MIS device
This shows a front-illuminated CCD. The more sensitive CCD’s are back illuminated

19. In a CCD pixel, photons are converted to electrons and stored in the potential well

20. The readout works like conveyor belts of light buckets

21. The result is an array of numbers representing brightness

22. The array of data is translated into a grey scale image

23. The digital camera works on the same principle as a CCD
The color camera puts micro-filters in front of each pixel and then electronically adds the different colored pixels together to make a color image

24. Video Astronomy

25. There are two reasons to do video astronomy
Reason 1: precise timing of astronomical events like occultation’s or meteor showers.

26. Reason 2: a poor man’s adaptive optics
Ganymede imaged by Brad Hill taken on Thanksgiving morning in Nashville using a C14 and Flea 3 video camera