5.3 Spectroscopy in Astronomy

Lights behaviour

Help with optical instruments

1. Reflection

2. Refraction

Dispersion

•  Seen using a prism to separate by wavelength

Any instrument used to disperse light is called a spectrometer

Stellar Spectra: 

• Some gases absorb different colour wavelengths and show dark bands at the points they don't absorb, being different for all gases

Spectral signatures

• Distinctive emitted wavelengths for a substance

  • Each atoms emission helps identify an objects elements 

Line Spectra:

a series of discrete, narrow lines of specific wavelengths produced by a light source or absorbing medium → Two types of line spectra

Emission Spectrum:

1.  Produced when an excited atom or ion drops down to a lower energy level and releases energy as photons of light. 

• Electron will emit energy after being energized/excited (unstable) when it’s returning to its ground state (stable), the energy is seen as a line spectrum/ emission spectrum

Different Levels that the Hydrogen Electron can fall to:

1. Lyman: UV light, Electron falls to level 1

2. Balmer: VIsible light, Electron falls to level 2

3. Paschen: Infrared light, Electron falls to level 3

4. brackett : infrared light to n=4

5. pfund : infrared light to n 5

• The level where electrons start their upward jumps in a gas can serve as an indicator of how hot that gas is

Absorption spectrum

1. Produced when atoms in the ground state absorb photons of specific energies to move electrons to higher energy levels. 

• Absorption spectrum is the opposite of emission as it’s how much energy is added to bring it up a level (seen on a rainbow background) 

Ionization Energy: 

• When an electron is “excited” it jumps between shells, however, some can be bushed so far it is no longer in the nucleuses orbit/attraction (convergence limit)

  • This Loss of electrons is called: Ionization

• Ionization Energy: Energy required to remove an electron from the outermost shell from an atom in a gas phase

• Can only occur in the gas phase

Solar Spectrum

Use absorption spectrum to give evidence of what elements are absorbing those specific wavelengths