| |
Device |
Spectral Range |
Comments |
| 1. |
Eye |
Visible Light
(Violet
to
Red only)
About
400
to
700 nm
|
- Peak sensitivity (Green)
- Daylight
photopic
(Yellowish-Green)
- Dark Adapted
scotopic)
(Bluish-Green)
|
|
| 2. |
Photographic Emulsion
(on Glass or Film) |
X Rays
to
IR
|
Originally sensitive only to blue
- Today emulsions put on
thin sheets of plastic (film)
- Glass still used
(flat, won't curl with age, etc.)
- Used to find stellar magnitudes
(photoelectric photometer more precise)
|
 |
| 3. |
CCD
(Charged
Couple
Device) |
UV
to
IR |
How Works
- Hundreds of thousands or millions of tiny, light sensitive cells (pixels)
- Light builds electric charge
- Charge sent to storage unit
- Sent to computer
- Computer reconstructs image
(using charge & location of each pixel)
- Used in modern video cameras
CCD Advantage
- Very efficient
(Good red sensitivity)
- Shows objects 10-20x fainter than photography (same exposure)
- Records same detail with less exposure
- Digital images easily manipulated & stored
|
 |
| 4. |
Photoelectric
Photometer |
UV
to
IR
|
What Does
- Attaches to telescope
- Contains a photoelectric multiplier tube
- Extraordinarily sensitive "light meter"
(originally sensitive only to blue)
- Used to measure accurate stellar magnitudes
How works
- Light goes in
- Converted to weak electric signal
- Electric signal multiplied
- Electric signal goes out
|
 |
| 5. |
Spectrograph |
X Rays
to
IR
|
- Attaches to telescope
- Probably most widely used astro instrument
- Contains a diffraction grating
- Produces spectra
(originally sensitive only to blue)
- See Study Guide Table 8
|
 |
