1. Emily Linden & Fiona Ward
Interstellar Matter
Emily Linden & Fiona Ward

2. Question
Specify the radio techniques used to probe the nature of interstellar matter.

3. Book example Optical Spectral Analysis Requires
-Background source of radiation
-Stars viewed through clouds to be relatively close to earth (w/in a few thousand pcs)
Low-energy Radio Emissions produced by the gas of the nebula itself is more versatile
Astronomers examine hydrogen spin-rates to determine radio spectral lines
Hydrogen 21-Centimeter Radiation

4. Book Example
Hydrogen ground state spin patterns: parallel or antiparallel
Antiparallel has slightly less energy than parallel
All matter tends to achieve lowest possible energy state.
When hydrogen atom drops down to antiparallel spin, a photon is emitted.
High energy  low energy: Emitted photon is equal to energy lost
Energy difference is very low, so energy of photon is very low
Wavelength= 21.1 cm (radio portion)
21-centimeter radiation: the spectral line that results from this hydrogen-spin-flip process

5. Book Example Requires no visible light
Can be used on any interstellar region that contains enough hydrogen gas to produce a detectable signal
This includes low-density regions between dark clouds
Wavelength much larger than typical interstellar dust particles
Radio radiation reaches Earth unscattered by interstellar debris
Can reach well beyond a few thousand parsecs
Can reach in directions lacking background stars

6. Ultraviolet, Visible, and infrared
Ultraviolet, Visible, and infrared
Hubble's Wide Field Planetary Camera 2 in 1994, 1995, and 2001
Color filters were used to isolate light emitted by hydrogen, oxygen, nitrogen, and sulfur atoms
This nebula is an emission
NGC 604 (Nicolas-Claude Fabri de Peiresc.)
First noted by the English astronomer William Herschel

7. Gravitational Lens Radio signals will be sent out
Gravitational Lens
Radio signals will be sent out
Usually up to five satellites in space
Higher the frequency the father the distance

8. Reflection Nebula Gives off a blue color
Reflection Nebula
Gives off a blue color
The star Rigel supplying the light
Retains light from other source

9. Answer
Book Example: Astronomers use Hydrogen 21-Centimeter Radiation to probe the nature of interstellar matter.
Web Example: Astronomers use cameras from telescopes such as Hubble equipped with color filters and radio emissions to probe the nature of interstellar matter.