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-P7- > P7.3 > Flashcards

P7.3 Flashcards

1
Q
  1. What does parallax stars do to closer stars?
A

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

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2
Q
  1. What is the parallax angle of a star?
A

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

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3
Q
  1. What does a smaller parallax angle mean?
A

-the star is further away

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4
Q
  1. What is a parsec (pc)?
A

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

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5
Q
  1. What is one arc second?
A
  • 1”

- 1/3600 degrees

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

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

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7
Q
  1. How many light years is one pc?
A

-1 pc= 3 light years

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8
Q
  1. What are typical interstellar distances?
A

-a few parsecs

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9
Q
  1. What does the luminosity of a star depend on?
A
  • its temperature

- its size

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10
Q
  1. What does the observed intensity of light from a star (as seen on Earth) depend on?
A
  • luminosity

- distance from Earth

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11
Q
  1. How could stars with different luminosities and distances from earth have the same observed brightness?
A
  • far and luminous

- close and less luminous

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12
Q
  1. What do Cepheid variable stars do?
A

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

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13
Q
  1. What is a pulse period?
A

-the time in-between pulses

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14
Q
  1. What is the relationship between luminosity and pulse period in Cepheid variables?
A

-bigger luminosity=bigger pulse period

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15
Q
  1. How can astronomers to estimate the distance to Cepheid variable stars?
A
  • stars with the same observed brightness

- ones with a longer pulse period= higher luminosity= further away

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16
Q
  1. 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?
A
  • 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
17
Q
  1. What did telescopes reveal about the Milky way galaxy regarding stars?
A
  • that the Milky Way consists of millions of stars

- led to the realisation that the Sun was a star in the Milky Way galaxy

18
Q
  1. What did telescopes reveal the existence of?
A

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

19
Q
  1. What was the main issue in the Curtis-Shapley debate?
A

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

20
Q
  1. What were Shapley’s arguments?
A
  • 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
21
Q
  1. What were Curtis’ arguments?
A
  • universe made up of many galaxies
  • smaller galaxy, 10k pc wide
  • sun/solar system near centre
  • nebulae= distant galaxies
  • galaxies separate to Milky Way
22
Q
  1. Who was right in the Curtis-Shapley debate?
A 
Shapley:
-sun/solar system were far from centre
Curtis:
-universe made up of many galaxies
-nebulae= distant galaxies
-galaxies separate to Milky Way
23
Q
  1. What did Hubble’s observations of Cepheid variables in one spiral nebula indicate? What did he conclude from this?
A
  • that it was much further away than any star in the Milky Way
  • he concluded that this nebula was a separate galaxy
24
Q
  1. What are intergalactic distances typically measured in?
A

-megaparsecs (Mpc)

25
Q
  1. What has data on Cepheid variable stars in distant galaxies done?
A

-given better values of the Hubble constant

26
Q
  1. How do you calculate speed of recession?
A

Speed of recession= Hubble constant x distance

27
Q
  1. What suggests space is expanding?
A
  • motions of galaxies
  • redshift
  • Hubble constant (speeding up further away)
28
Q
  1. How do scientists believe the Universe began?
A

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

29
Q
  1. What is the big bang theory?
A

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

-P7- (6 decks)

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