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Lecture

# ASTA02H3 Lecture Notes - Photosphere, Hydrogen Spectral Series, Lyman Series

Department
Astronomy
Course Code
ASTA02H3
Professor
Parandis Khavari

Page:
of 4
Astronomy - Session 3
absorption of a photon
used as electricity to move into higher orbit
light > beam of particles with energy > photon
excited atom
emission of a photon
1. absorption of a photon with right energy
2. collision with other atoms
1. and 2. are methods to excite an atom
atoms are not always excited
absorbed photons will be emitted
produce emission line
cannot make energy
do you think an absorbed photon can be emitted as two photons?
what conditions must be satisfied?
signature emission/absorption line produced by each atom
why does each atom do that?
the phrase, "each atom" is equivalent to "different elements"
ex. why does Hydrogen and Helium make different radiation?
Professor's explanation:
each element has a unique construction
ex.
different level in orbits
ex.
Lyman series
from 1 to higher orbits
ultraviolet rays
orbits called n=x
Balmer series
ultraviolet rays are visible
n=2
Paschen series
IR
n=3
Q. why is Hydrogen so important in astronomy?
A. it was one of the first elements created in the Big Bang and is the most abundant
any element other than Hydrogen and Helium is called a "metal" in astronomy
high ultraviolet low IR
Q. why do Paschen series appear in IR while Lyman series appear in ultraviolet?
A. different energy and different orbital levels reults in a difference
closer to the nucleus
need more energy to move
Lyman series needs more energy
ex. n=1 > n=3 and n=3 > n=5
ex. E 1-3 > E 3-5
note: E 1-3 = Lyman
absorb/emit Hydrogen
transitions from 1 orbit to the others
to what transition does Paschen (gamma) line refer to
ex. line 3-6
relative strength absorption line is a measure of temperature
absorption line tells us about the rotation, composition, gravity of a star
light from a start from photosphere
responsible for formation of spectrum
strength of absorption lines
surface temperature less than or equal to the Sun
few violent
higher temperature > faster movement > more excited