Transcript Stars --- Color, Temperature, Brightness, Parallax

Unit 6 --- Sixth Grade
http://www.youtube.com/watch?v=QZDk1cbKp7s&feature=related&safety_mode=true&persist_safety_mode=1
But they are actually
huge, hot bright balls
of gas that are trillions
of kilometers away
from Earth
 The Sun is our closest
star, it’s 93 million
miles away, and it
takes about 8 minutes
for its light to reach us
on Earth.



The next closest star is
Proxima Centauri, located
4.2 light years away.
A light year is the distance
light travels in a single year
– 9,460,528,000,000
kilometers, or
5,865,696,000,000 miles
▪ Approximately 6 trillion
 The light we see from
Promima Centauri left the
star 4.2 years ago

It would take our fastest
spacecraft 50,000 years to
reach Proxima Centauri!

Stars are made of
different elements in the
form of gases.
 On average, stars are 70
percent hydrogen and 28
percent helium
 Our Sun is 91% hydrogen
and 9% helium


The inner layers are very
dense and hot
The outer layers are
made of cooler gases

Because different
elements absorb
different wavelengths of
light, astronomers can
tell what a star is made
of from the light they
observe from the star
 A Spectragraph breaks
down a star’s light into a
spectrum
▪ From the colors on the
spectrum, astronomers can
determine what a star is
made up of

In the 1800’s, aided by their spectragraphs,
astronomers started to collect and classify
the spectra of many stars.

At first, they were classified according to
their composition, but that system was
found to be flawed, and we now classify stars
according to how hot they are.
Class
Color
Surface temp
Elements
Examples
O
Blue
Above 30,ooo C helium
1o Lacertae
B
Blue-white
10,000-30,000C Helium and
hydrogen
Rigel, Spica
Blue-white
7,500-10,000 C
hydrogen
Vega, Sirius
F
Yellow-white
6,000-7,500 C
Hydrogen,
heavier
elements
Canopus,
Procyon
G
Yellow
5,000-6,000 C
Calcium, other
metals
The Sun,
Capella
K
orange
3,500- 5,000 C
Calcium,
molecules
Arcturus,
Aldebaran
M
red
Less than 3,500 molecules
C
A
Betelgeuse,
Antares


Stars are further classified
by their brightness, or
how brightly they shine in
the sky.
At first, they were given
numbers to indicate their
brightness
 The brightest stars were
called first-magnitude
stars
 The dimmest were sixthdegree magnitude stars


But when astronomers began to use telescopes, they began
to see many stars they hadn’t discovered because they were
so dim.
They added to their scale of magnitudes
 Bright stars had a negative number
 Dim stars had a positive number

Look at the picture ---

Do all the lights look the
same?

Do some appear to be
brighter or dimmer?


Why?
The ones closer appear to
be brighter, and the ones
further away appear to be
dimmer.
The same thing applies
with stars!



The apparent brightness
of a star from Earth is its
apparent magnitude.
Apparent magnitude
depends on how close
the star is to the Earth
 Closer stars appear to be
brighter
▪ The Sun’s apparent
magnitude is -26.8,which
means it is the brightest
object in the sky (if you are
on Earth)
 Stars that are farther away
appear to be dimmer.



Absolute Magnitude is the
actual brightness of a star.
Astronomers "pretend" to
line up stars exactly 10
parsecs (about 32.6 light
years) away from Earth.
They then figure out how
bright each star would
look.
 They call that brightness the
star's absolute magnitude.
▪ In all actuality, the Sun is not an
especially bright star.
▪ The Sun has an absolute
magnitude of 4.83.

As mentioned earlier, the unit of measurement used to
measure the distances to stars is the light-year.

It is not a measurement of time as the name implies, it’s a
measurement of distance.

One light year is equal to 9,460,528,000,000 kilometers, or
5,865,696,000,000 miles (6 trillion)

Since it would be very hard to run a measuring tape up
into space for millions, billions and trillions of miles,
astronomers use other methods to measure a star’s
distance from Earth



Some stars, the ones
that are closest to Earth,
appear to move, while
those that are far away
appear to stay in one
place.
This apparent shift is
called parallax
Astronomers use
parallax and math to find
the actual distances to
stars that are close to
Earth