Questions and Answers
What are some of the rungs on the cosmic distance ladder? (Select all that apply)
How does trigonometric parallax work and what distance range does it cover?
Involves measuring the annual change in position of nearby stars relative to background ones over the course of the year; accurate for objects no more than 1000 parsecs away.
How does spectroscopic parallax work and what distance range does it cover?
Measuring the apparent brightness, spectral type, and luminosity class of a star gives an estimate of its luminosity, which then provides a distance estimate of up to 50 kpc.
How do Cepheids and RR Lyrae stars work and what distance ranges do they cover?
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How does the Tully Fisher relation work and what distance range does it cover?
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How does Type Ia supernovae work and what distance ranges does it cover?
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How is the distance ladder used?
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Study Notes
Cosmic Distance Ladder Rungs
- Key methods include trigonometric parallax, spectroscopic parallax, Cepheid and RR Lyrae variables, Tully-Fisher relation, and Type Ia supernovae.
Trigonometric Parallax
- Measures the annual positional shift of nearby stars against distant background stars as Earth orbits the Sun.
- Applicable for stars within 1000 parsecs (3,260 light-years).
Spectroscopic Parallax
- Estimates a star's luminosity by analyzing its apparent brightness, spectral type, and luminosity class.
- Can gauge distances up to 50 kiloparsecs (kpc).
Cepheids and RR Lyrae Variables
- Variable stars whose luminosities correlate with their pulsation periods; crucial for distance measurement.
- Cepheids are more massive, while RR Lyrae stars are less massive and both have left the main sequence.
- Effective for distances between 30 to 40 megaparsecs (Mpc).
Tully-Fisher Relation
- Links the rotational velocity of spiral galaxies to their luminosity; more massive galaxies spin faster and emit more light.
- Distance estimation achieved through analyzing the rotation curve of galaxies, applicable up to a few hundred megaparsecs, but with imprecision.
Type Ia Supernovae
- Brightness decay rates serve as "standard candles" for distance measurement.
- Detectable across several hundred megaparsecs and provide relatively precise distance estimates, though occurrences in individual galaxies are infrequent.
Application of the Distance Ladder
- Establishes the universe's physical scale by correlating redshift with recessional velocity and distance via Hubble's law.
- Utilizes redshifts from known-distance objects to measure cosmic expansion changes.
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Description
Test your knowledge on the cosmic distance ladder with flashcards focusing on key concepts like trigonometric parallax and various types of variable stars. This quiz covers essential methods used in measuring astronomical distances, making it perfect for students preparing for an astronomy exam.
