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Chapter 29.2 Measuring Stars

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

 

Useful power ch 25

  1. 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.

  1. how big the star is
  2. how hot the star is
  3. 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?

  1. size
  2. temperature
  3. 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.

 

H-R 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

 Use this link to answer 17 questions about the HR diagram.

 

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

Tools for studying stars

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

https://www.youtube.com/watch?v=sqwgpsXII0s