1. Stars, starlight
AND
Light
Information

2. OUTCOME QUESTION(S): S1-4-06: S1-4-07:
How do astronomers measure the great distances in the universe?
S1-4-07:
What can an astronomer learn about a star by looking at light?
Vocabulary & Concepts 
Astronomical Unit Light-year
Apparent magnitude Absolute magnitude
Electromagnetic Energy Spectroscope

3. Scientific Notation (x 10X) Express very large or very small numbers
“Power of 10” equals the number of places the decimal was moved (+) large, (-) small
is x 107
is x 10-9
2.6 x is
2.6 x is
A positive exponent (107) means multiply by 10 that many times
A negative exponent (10-5) means divide by 10 that many times

4. Earth to the Sun: 1 AU = 1.5 x 108 km (150000000)
Distance and the Universe
Common to use Astronomical Unit (A.U.)
1 A.U. = distance between the Earth and the Sun
Common Distances:
Sun - Pluto: ~ 40 AU Sun - Saturn: ~ 10 AU
Sun - Jupiter: ~ 5 AU Sun - Mars: ~ 1.5 AU
So Pluto is 40x farther away from the Sun than Earth
Earth to the Sun: 1 AU = 1.5 x 108 km ( )

5. Nearest star - 4.1 x 1013 km away from Earth!
That’s 41,000,000,000,000 km!
Nearest star x 1013 km away from Earth!
This star is Proxima Centari
Light-year (LY):
The distance a beam of light travels in one year
Light moves outward fast – about 300,000 km/sec.
9.46 x 1012 km /year = 1 light-year
P. Centari is 4.3 light-years away

6. Bright stars look close, but may be very far away
Distances can be deceiving:
Bright stars look close, but may be very far away
Star Approx. Distance (LY)
P. Centari
Sirius
Betelguese
Rigel
Most distant known galaxy 15,000,000,000
Star light takes years to get to Earth – this delay means we are looking at old “images” – it’s like looking into the past…

7. Luminosity (brightness)
Star light can be used to determine temperature, composition and size (mass)
Luminosity (brightness)
There are two amounts (magnitudes) of brightness:
Apparent magnitude – brightness as we see it.
Absolute magnitude – actual brightness.
The Sun has a higher apparent magnitude, since it is so much closer than other stars

8. Star B looks brighter – more apparent magnitude
Star B is closer to us than Star A
Star B and A have the same absolute magnitude

9. Despite being cooler, the Sun is still bigger than about 95% of stars
Temperature of Colour
Colour – shows how much energy a star emits.
Colder star glows red
Hotter star glows bluish white or even blue
Colour
Temperature (oC)
Example
Blue
25,000 – 50, 000
Bluish-white
11,000 – 25,000
Rigel (Orion’s belt)
White
7,500 – 11,000
Sirius (brightest)
Yellowish-white
6,000 – 7,500
Polaris
Yellow
5,000 – 6,000
Sun
Orange
3,500 – 5,000
Red
2,000 – 3,500
P. Centauri (closest)
Despite being cooler, the Sun is still bigger than about 95% of stars

10. Notice bigger stars are not necessarily hotter…but usually brighter

11. Star Composition
Light is a type of energy called:
Electromagnetic Energy
Scientists use a spectroscope to analyse the light energy coming from stars
Spectroscope – tool that splits light into a pattern of colours, like a rainbow.

12. Showing as the “black” lines of missing energy
The elements that make the star will absorb unique parts of the spectrum as energy is released.
Showing as the “black” lines of missing energy
The black lines in the spectrum are used to identify the elements that make up the star.

13. Remember your chemistry: heated compounds give off a unique colour spectrum.
Scientists have heated elements and recorded the unique light energy patterns
The “missing” black lines in the spectra of the Sun match with the known spectra of Hydrogen but not with Mercury – so the Sun contains Hydrogen!

14. CAN YOU ANSWER THESE QUESTIONS? S1-4-06:
How do astronomers measure the great distances in the universe?
S1-4-07:
What can an astronomer learn about a star by looking at light?
Vocabulary & Concepts 
Astronomical Unit Light-year
Apparent magnitude Absolute magnitude
Electromagnetic energy Spectroscope