Spectroscopy is used to determine the composition of stars. When star light is passed through a prism or spectrograph, it separates into a spectrum of colors that can be analyzed. Each element emits or absorbs light at specific wavelengths, creating lines in the spectrum that act as a fingerprint to identify the elements present. By examining the spectra of unknown stars and matching the line patterns to known elements, astronomers can determine what chemicals stars are made of.

1. How do they know what stars
are made of?
Waves
Spectrography
Planet X
The Earth

2. Waves
• Wavelength(λ): distance between consecutive crests
• Frequency (f): number of oscillations per second
• v = λ·f
• c = λ·f (electromagnetic wave)
fhE
c
f




3. Electromagnetic spectrum

4. Electromagnetic spectrum

5. Electromagnetic spectrum

6. Spectrography
• White light is
made up of all the
colors of the
visible spectrum.
• Passing it through
a prism separates
it.

7. Non white light
• By heating a gas or
with electricity we
can get it to give off
colors.
• Passing this light
through a prism
does something
different.

8. Emission & absorption spectra
continuous spectrum
absorption spectrum
emission spectrum
hot source
gas

9. Bohr model
• Electrons exist only in
orbits with specific
amounts of energy called
energy levels
• Therefore…
– Electrons can only gain or
lose certain amounts of
energy
– Only certain photons are
produced
– Energy of photon depends
on the difference in energy
levels
1
2
3
4
5
6
nucleus

10. Hydrogen spectrum
A B C D E F
Lyman series (UV)
A B D E
Balmer (Visible)
A B C D
Paschen (IR)
E1
E2
E3
E4
E5
E6
Energy
IR
region
UV
region
656 nm
486 nm
434 nm
410 nm
ionization

11. Planet X
• What are planet X atmosphere made of?
Hydrogen
HelioHelio
Helium

12. Planet X
• What are planet X atmosphere made of?
Sodium
HelioHelio
Carbon

13. Planet X
• What are planet X atmosphere made of?
Chlorine
HelioHelio
Oxígeno

14. Planet X
• What are planet X atmosphere made of?
Nitrogen
HelioHelio
Oxygen

15. The Earth
• Which is the Earth atmosphere spectrum?
Nitrogen
HelioHelio
Oxygen
Earth 1

16. The Earth
• Which is the Earth atmosphere spectrum?
Nitrogen
HelioHelio
Oxígeno
Earth 2

17. The Earth
• Which is the Earth atmosphere spectrum?
Nitrogen
HelioHelio
Oxygen
Earth 4

18. The Earth
• Which is the Earth atmosphere spectrum?
Nitrogen
HelioHelio
Oxygen
Earth 3