# stars

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```					The Stars, Galaxies, and
Universe
Light: The Astronomer’s Friend!
This is what you just saw. The prism
refracts (bends) the light and
divides it up into its component
parts.
Before we can study stars, we must
study the light that comes from
them. For, it is this light that tells
us everything that we want to know

A nebula, the birthplace of stars
Stars give off different types of light.
We need to use these different
types of light to study them. This
involves using the electromagnetic
spectrum.
Mr. T gives off a different type of light
too. What kind of light is this?
Mr. T gives off a different type of light
too. What kind of light is this?

Visible     Infrared (FLIR)
Camera      Camera

Infrared!   Visible
Light is a form of electromagnetic
similar to the waves on the ocean.
Waves have certain parts to them. The
crest is the highest part, and the
trough is the lowest part.
The amplitude of a wave is the distance
from the center of the wave to the
crest (or trough). It is ½ of the
wave height. Amplitude is usually
measured in the base unit of
meters.

Wave height
The wavelength of a wave is the
distance from one crest to the next
crest, or one trough to the next
trough.
The Greek letter lambda () means
wavelength.






The wavelength of a wave is measured
in the base unit of meters. Because
the waves are usually small, they
are measured in μm (micrometers)
or nm (nanometers). 1 μm = 1 X
10-6 m and 1 nm = 1 X 10-9 m





The frequency of a wave is a measure
of how many wave crests pass a
certain point in a certain time. The
more waves, the higher the
frequency. The less waves, the
lower the frequency.
The Greek letter nu () means
frequency
The frequency of a wave is measured
in units called hertz (Hz). 1 hertz =
1 cycle per second.
frequency of 106.7 MHz, KFWB
frequency of 980 KHz, and my radio
control airplane works on a
frequency of 72.670 MHz.
Electromagnetic waves are the result of electricity
and magnetism working together. The Blue
arrows show the electric field and the red
arrows show the magnetic field. The fields
are perpendicular to each other and to the
direction of the wave.
Electromagnetic waves travel at the
speed of light, which is measured to
be 3.0 X 108 meters/second or
186,000 miles/second or
669,600,000 miles/hour?
The speed of light (c) is equal to the
frequency () times the wavelength
().

c=x
How are energy, frequency, and
wavelength related? Go here to find
out.
Here is the calculation for radio station
KROQ at 106.7 MHz, or
106,700,000 Hz = 106,700,000
cycles/second.

300,000,000 meters/second
= 106,700,000 cycles/second
X 2.81 meters
The light that you see and the
beforehand are all part of the
electromagnetic spectrum.
Here is a NOVA tour of the
electromagnetic spectrum.
So, How do we know what stars are
made of is we can’t go to them
to sample their chemistry?
We use a method called spectroscopy,
where the spectra of a star is
analyzed. We separate the light
coming from a star by using a tool
called a spectroscope.
We then analyze the spectra, or
colors, that a star emits (gives
off) or absorbs.
The spectra below is referred to as
a continuous spectrum. Light
from all visible wavelengths is
being emitted.

A continuous spectrum is emitted from glowing
solids (a light bulb), glowing liquids (molten
iron), and the hot compressed gases inside
stars
The second spectra below is referred to as
an emission spectrum. Light from only
certain wavelengths is being emitted.

Each chemical element emits a different pattern
of light. We can analyze these patterns to
determine what chemical element(s) is(are)
in a star.
Go here for an example of various
emission spectra for different
gases.
The third spectra below is referred to as an
absorption spectrum. Light from only
certain wavelengths is being absorbed
by the cooler gas it passes through.

“By comparing emission and absorption spectra,
scientists can determine what elements are
present in the cooler gas that is absorbing
some of the light.”
We can also use absorption spectra to
determine the composition of a planet’s
atmosphere.

“If the spectrum of the reflected light from a
planet contains dark lines not contained in
the sun’s spectrum, then these lines must be
caused by substances in the planet’s
atmosphere.”
Sources of Continuous, Emission, and
Absorption Spectra

Continuous: From a light bulb or hot metal
Emission: From light emitted from a hot gas
Absorption: From light that passes through a
cooler gas
The Doppler Effect.

We can measure the amount of blue-shift or red-
shift in a star’s spectrum to determine if a
star is moving towards us or away from us.
The Doppler Effect.

You have experienced the Doppler Effect before
with police cars. If the police car comes
toward you, the higher pitch (shorter
wavelength) you hear.
The Doppler Effect.

You have experienced the Doppler Effect before
with police cars. If the police car moves
away from you, the lower pitch (longer
wavelength) you hear.
The Doppler Effect.

If a star is moving towards us, we will see a blue-
shift. This is because the wavelengths of
light are compressed into the shorter blue
wavelengths.
The Doppler Effect.

If a star is moving away from us, we will see a
red-shift. This is because the wavelengths of
light are expanded into the longer red
wavelengths.
The Doppler Effect.

The spectra of a star reveal which direction a star
is moving.
The Doppler Effect.

A cosmological red-shift indicates that stars and
galaxies are moving away from us. As Mr.
Auld pointed out, this means that our
Universe is expanding, or moving outwards.
WOW!
Stars and Their
Characteristics
How many stars are in our galaxy? How
many galaxies are in our Universe? The
stars that you see with the naked eye
are only within our Milky Way Galaxy.
What is the difference between astrology
and astronomy?
Astrology is a belief that the stars and
planets can influence human life in a
mystical fashion.
Astronomy is a science that attempts to
explain the Universe and everything
within it. We are studying astronomy in
this class.
We call groups of stars constellations.
These are names given to groups of
stars by ancient astronomers.
Constellations help us to find stars. Go

The Constellation Orion
The positions of constellations change
throughout the year because of Earth’s
revolution around the sun.
The Constellation Orion   The Constellation Scorpius is
is visible in Winter      visible in Summer
The Apparent Magnitude is how bright a star
appears from the Earth. The lower the Star’s
apparent magnitude, the brighter the star is.
Negative magnitudes are the brightest stars.
For each increase of 1 in apparent
magnitude, relative brightness increases by
2.5 times.
magnitude    0   1    2   3     4     5     6    7    8     9     10

Relative     100 4000 160 630   250   100   40   16   6.3   2.5   1
brightness
00       0
Star distances are measured in units
called light years. A light year is the
distance that light travels in one
year.

If light travels at 186,000 miles per
second or 686,600,000 miles per
hour, then how many miles is one
light year?
Star Parallax, an apparent shift
in star position, is a method
of measuring distances to the
nearest stars.
You use parallax every day.
What do you use it for?
Distance in parsecs = 1 / parallax
angle
1 parsec = 3.26 light years
1 parsec = 3.26 light years
Stars have different mass, size, and
temperature.
Star         Type           Solar masses Solar radii
Sirius       Main seq.      2.3          2.5
Rigel        Blue super     20           36
Betelgeuse   Red super      20           1,000
Aldebaran    Red giant      5            20
Deneb        Yellow Super   14           60
Capella      Red Giant      3.5          13
Pollux       Red Giant      4            8
Altair       Main seq.      2            1.5
Relative Sizes of Stars
Relative Sizes of Stars
Relative Sizes of Stars
Relative Sizes of Stars
Relative Sizes of Stars
Temperature and Color of Stars
Temp. (C)     Color          Elements     Class
> 30,000      Bluish white   Ionized He   Oh
9,500-30,000 Bluish white    Neutral He   Be
7,000-9,500   White          Metals, H    A
6,000-7,000   Yellow white   Metals, H    Fine
5,200-6,000   Yellow         Metals, H    Girl (or Guy)
3,900-5,200   Yellow         Metals, H    Kiss
orange
< 3,900       red            TiO2         Me
The Luminosity of a star is its actual
brightness.

Luminosity only depends on size
and temperature.
The Absolute Magnitude of a star is
how bright it would be if it were a
distance of 10 parsecs (32.6 light
years) from Earth.

This is different from apparent
magnitude because the apparent
magnitude does not account for the
distance to the star and the star’s
luminosity.
Apparent Magnitude vs. Absolute Magnitude
Star             Apparent Mag.     Absolute Mag.
Aldebaran        +0.87             -0.65
Algol            +2.09             -0.15
Antares          +1.06             -5.38
Betelgeuse       +0.45             -5.09
Capella          +0.08             -0.48
Polaris          +1.97             -3.59
Procyon          +0.41             +2.62
Rigel            +0.18             -6.75
Sirius           -1.44             +1.42
Spica            +0.98             -3.55
Cepheid Variable Stars can be used to
measure long distances to stars.
Cycles of brightness range from 1
to 50 days. A star with a cycle of 50
days would be brighter than a star
with a brightness range of 1 day.
Astronomers can calculate long
distances by comparing a Cepheid’s
apparent and absolute magnitude.
Life Cycles of Stars are shown
with a Hertzsprung-Russell
Diagram
Blue Super            Red Super
Giants                Giants

Main Sequence

White Dwarfs
Red Dwarfs
We gauge the Life Cycle of Stars
using the Hertzsprung Russell
(H-R) Diagram
Blue Super            Red Super
Giants                Giants

Main Sequence

White Dwarfs
Red Dwarfs
Another H-R Diagram
Click on this link to investigate
the different life cycles of
stars and how they relate to
the H-R Diagram.
The stability of a star depends
on the balance between
gravity pulling inward and
energy from nuclear reactions
pushing outwards.
Relativity and Black Holes
Albert Einstein was famous for his ideas on
relativity.
The Stars Study Quiz
The Stars Pre Quiz
“Agree,” “Disagree,” or
“Don’t Know” on a half
sheet of paper.
1. We know about stars by
analyzing the light that we
see.
2. Stars have life cycles,
which last many many
years.
3. The Universe is becoming
smaller.
4. Stars are much closer to
us than the planets are.
5. Hotter stars are red in
color.

```
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 views: 12 posted: 6/5/2011 language: English pages: 79