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Flashcards in P7.3 Deck (29):

1. What does parallax stars do to closer stars?

-parallax makes closer stars seem to move relative to more distant ones over the course of a year


2. What is the parallax angle of a star?

-half the angle moved against a background of very distant stars in 6 months


3. What does a smaller parallax angle mean?

-the star is further away


4. What is a parsec (pc)?

-the distance to a star with a parallax angle of one second of arc


4. What is one arc second?

-1/3600 degrees


6. What is a parsec similar in magnitude to, what do astronomers use it to do?

-a light-year and is the unit used by astronomers to measure distance


6. How many light years is one pc?

-1 pc= 3 light years


7. What are typical interstellar distances?

-a few parsecs


8. What does the luminosity of a star depend on?

-its temperature
-its size


9. What does the observed intensity of light from a star (as seen on Earth) depend on?

-distance from Earth


6. How could stars with different luminosities and distances from earth have the same observed brightness?

-far and luminous
-close and less luminous


10. What do Cepheid variable stars do?

-pulse in brightness, with a period related to their luminosity


10. What is a pulse period?

-the time in-between pulses


10. What is the relationship between luminosity and pulse period in Cepheid variables?

-bigger luminosity=bigger pulse period


11. How can astronomers to estimate the distance to Cepheid variable stars?

-stars with the same observed brightness
-ones with a longer pulse period= higher luminosity= further away


12. What was the role of observations of Cepheid variable stars in establishing the scale of the Universe and the nature of most spiral nebulae as distant galaxies?

-Hubble worked out the distance to a spiral nebula using Cepheid variables (and their relationship between brightness and pulse period)
-he found that the nebula was further than any stars in Milky Way= must be a separate galaxy


13. What did telescopes reveal about the Milky way galaxy regarding stars?

-that the Milky Way consists of millions of stars
-led to the realisation that the Sun was a star in the Milky Way galaxy


14. What did telescopes reveal the existence of?

-many fuzzy objects in the night sky, originally called nebulae


15. What was the main issue in the Curtis-Shapley debate?

-whether spiral nebulae were objects within the Milky Way or separate galaxies outside it


15. What were Shapley’s arguments?

-universe was one giant galaxy
-100k parsecs wide
-sun/solar system were far from centre
-nebulae= clouds of gas/dust
-clouds part of Milky Way


15. What were Curtis’ arguments?

-universe made up of many galaxies
-smaller galaxy, 10k pc wide
-sun/solar system near centre
-nebulae= distant galaxies
-galaxies separate to Milky Way


15. Who was right in the Curtis-Shapley debate?

-sun/solar system were far from centre
-universe made up of many galaxies
-nebulae= distant galaxies
-galaxies separate to Milky Way


16. What did Hubble’s observations of Cepheid variables in one spiral nebula indicate? What did he conclude from this?

-that it was much further away than any star in the Milky Way
-he concluded that this nebula was a separate galaxy


17. What are intergalactic distances typically measured in?

-megaparsecs (Mpc)


18. What has data on Cepheid variable stars in distant galaxies done?

-given better values of the Hubble constant


19. How do you calculate speed of recession?

Speed of recession= Hubble constant x distance


20. What suggests space is expanding?

-motions of galaxies
-Hubble constant (speeding up further away)


21. How do scientists believe the Universe began?

-with a ‘big bang’ about 14 thousand million years ago


21. What is the big bang theory?

-universe expanded from a single point, and is still expanding today