Quiz Question: jglenn/courses/astr_1120/ppt_lectures/classification.pdf same intrinsic luminosity)....

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Transcript of Quiz Question: jglenn/courses/astr_1120/ppt_lectures/classification.pdf same intrinsic luminosity)....

  • Imagine three identical stars (meaning that they have the same intrinsic luminosity). The apparent magnitudes of the stars are given below; which star is the most distant?

    A)m=8 B)m=10 C)m=12

    Quiz Question: Magnitudes

  • Imagine three identical stars (meaning that they have the same intrinsic luminosity). The apparent magnitudes of the stars are given below; which star is the most distant?

    A)m=8 B)m=10 C)m=12

    Star C has the largest apparent magnitude, hence it is the most distant.

    Quiz Question: Magnitudes

  • The absolute magnitude of a star is its luminosity.

    The apparent magnitude of a star is its perceived brightness.

    Brightnesses, Luminosities, & Magnitudes

  • •How do astronomers measure the distances to nearby stars? •How do we get stellar masses from binary stars? •How do we classify stars?

    Questions

  • Fig. 16.3

    Using the motion of the Earth to measure distances to stars

    Recall: 1" = (1/60) of 1' 1' = (1/60) of 1°

    Distance (parallax seconds) = 1/parallax(")

    1 parallax second = 1 parsec = 3.26 light years = 3.1x1016 m

    d(pc) = 1/p(")

    Stellar Parallax: Measuring the Distances to Nearby Stars

  • The closest star to the Sun

    Sun Proxima CentauriEarth

    Golf Ball

    Grain of

    Sand

    Golf Ball

    1m 270km

    Proxima Centauri is a little closer to the Sun than the average separation between stars in the Milky Way.

    Case Study: Proxima Centauri

  • d(pc) = 1/p(“)

    What is the distance, in parsecs, to Proxima Centauri, given that it’s parallax angle is 0.76“?

    A)0.76 pc B)1.3 pc

    Concept Question: Proxima Centauri Parallax

  • d(pc) = 1/p(“)

    What is the distance, in parsecs, to Proxima Centauri, given that it’s parallax angle is 0.76“?

    A)0.76 pc B)1.3 pc

    d(pc) = 1/0.76“ = 1.3 pc

    Concept Question: Proxima Centauri Parallax

  • Although you cannot see it, stars are moving in all 3 dimensions.

    α Cen22 km/s

    -20 km/s (blueshift)

    30 km/s net motion

    Sun

    Stellar Motions: α Centauri

  • Astronomers use the relative motion of stars in binary systems, along with Kepler’s laws, to measure the masses of stars.

    (Approximately half of all stars are in binary systems.)

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    1 6.

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    Rest positions

    Determining Stellar Masses: Binary Stars

  • Rest positions

    Which star is more massive? A)A B)B

    Concept Question: Binary Stars Masses

  • Rest positions

    Which star is more massive? A)A—Star A has a slower orbital velocity B)B

    Concept Question: Binary Stars Masses

  • Stars are classified based on their spectra, which are determined by their temperatures.

    Fig. 16.04

    1. Stars are like blackbodies: color ⇒ temperature

    2. Spectra absorption features allow a finer classification

    Stellar Classification

  • Study this table Stellar Classification: Spectral Sequence

  • Study this table

    Oh Be A Fine Girl Kiss Me

    Stellar Classification: Spectral Sequence

  • Fig. 16.10

    The Hertzprung-Russell Diagram