Ch 29.2 Measuring the Stars
Vocabulary:
parallax
binary star
light-year
apparent magnitude
absolute magnitude
nebulae
main-sequence star
red giant
super giant
nova
Cepheid Variable
- Objectives:
1. What can we learn by studying star properties?
- Color indicates temperature
- Parallax can be used to calculate the distance the star is from Earth
- Binary stars can be used to determine the stellar mass
- Stellar brightness is measured by the absolute magnitude and the apparent magnitude. The lower the number, the brighter the star.
Absolute brightness= how bright the star actually is
Apparent brightness = a star’s brightness as it appears from Earth
Three factors control apparent brightness.
- how big the star is
- how hot the star is
- how far away the star is
2. How does distance affect parallax?
- The closer the star is to Earth, the greater the parallax
- You cannot use a parallax to measure the distance to all stars as some stars may be so far away that the parallax angle is too small to measure.
- It takes 6 months to measure a star by its parallax as you have to wait for the Earth to reach the maximum distances of its orbit
3. What 3 factors determine a star’s apparent magnitude?
- size
- temperature
- distance from Earth
4. What relationship is shown on a Hertzsprung-Russell diagram?
Shows the relationships between the absolute magnitude and the temperature of stars.
Watch a short animation of the HR diagram.
What color stars are the hottest? Coolest?
Blue are the hottest
Red are the coolest
How do the stars on the left hand side of the diagram differ from stars on the right hand side of the diagram?
The stars on the left are the hottest, the stars on the right are the coolest
How do the stars on the top of the diagram differ from stars on the bottom of the diagram?
The stars toward the top are giant stars while the stars toward the bottom are smaller stars and dwarf stars
Properties of Light
Electromagnetic spectrum arrangement of waves according to their wavelengths and frequencies.
- gamma Short wavelength High frequency
- x-rays
- ultravoilet radiation
- visible light
- infrared
- microwaves
- radiowaves Long wavelength Low frequency
Doppler Effect the change in frequency of a wave due to movement of the source of the wave.
Wavelength are shortened as the source moves toward the observer and lengthened as the source moves away from the observer.
Short wavelengths are blue in color, long waves lengths are red in color.
What color would be the shift if a galaxy is moving away from Earth?
RED
Spectroscopy is the study of the properties of light that depend on wavelength.
Continuous spectrum includes
ROYGBIV mhttps://www.youtube.com/watch?v=bjOGNVH3D4Y&feature=related
Doppler Effect: mhttps://www.youtube.com/watch?v=Tn35SB1_NYI&feature=related
Fun Science mhttps://www.youtube.com/watch?v=LIvVzJ6KZpk
Optical Telescopes
Type of telescope | Pros and cons | |
Refracting | Uses lenses | Needs expensive lensesGlass lenses limit size |
Reflecting | Uses mirrors | Best optical quality- no size limit |
Chromatic Aberration the property of a lens where different colors are not in focus at the same time
Detecting “Invisible” Light
Type of telescope | Pros and cons | |
Radio telescope | Uses antennae to capture incoming radiowaves | Not affected by cloudsCan use 24 hours a dayCan detect cool clouds and gases |
Space telescope | Orbit above Earth’s atmosphere | Produce clearer images than Earth telescopes |
Special purpose | Examples X-ray telescope to study black holesCompton Gamma-Ray to study exploding stars | Can “see” objects outside of visible light spectrum |
Review video: NOVA Hunting the Edge of Space: Part 1