P7.3 Flashcards
- 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
- What is the parallax angle of a star?
-half the angle moved against a background of very distant stars in 6 months
- What does a smaller parallax angle mean?
-the star is further away
- What is a parsec (pc)?
-the distance to a star with a parallax angle of one second of arc
- What is one arc second?
- 1”
- 1/3600 degrees
- 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
- How many light years is one pc?
-1 pc= 3 light years
- What are typical interstellar distances?
-a few parsecs
- What does the luminosity of a star depend on?
- its temperature
- its size
- What does the observed intensity of light from a star (as seen on Earth) depend on?
- luminosity
- distance from Earth
- How could stars with different luminosities and distances from earth have the same observed brightness?
- far and luminous
- close and less luminous
- What do Cepheid variable stars do?
-pulse in brightness, with a period related to their luminosity
- What is a pulse period?
-the time in-between pulses
- What is the relationship between luminosity and pulse period in Cepheid variables?
-bigger luminosity=bigger pulse period
- 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
- 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
- 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
- What did telescopes reveal the existence of?
-many fuzzy objects in the night sky, originally called nebulae
- What was the main issue in the Curtis-Shapley debate?
-whether spiral nebulae were objects within the Milky Way or separate galaxies outside it
- 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
- 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
- Who was right in the Curtis-Shapley debate?
Shapley: -sun/solar system were far from centre Curtis: -universe made up of many galaxies -nebulae= distant galaxies -galaxies separate to Milky Way
- 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
- What are intergalactic distances typically measured in?
-megaparsecs (Mpc)
- What has data on Cepheid variable stars in distant galaxies done?
-given better values of the Hubble constant
- How do you calculate speed of recession?
Speed of recession= Hubble constant x distance
- What suggests space is expanding?
- motions of galaxies
- redshift
- Hubble constant (speeding up further away)
- How do scientists believe the Universe began?
-with a ‘big bang’ about 14 thousand million years ago
- What is the big bang theory?
-universe expanded from a single point, and is still expanding today
