2580213
Description
Flashcards by Josh Price, updated more than 1 year ago
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Created by Josh Price
over 9 years ago
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| Question | Answer |
| What is parallax? | The shifting of position against a fixed background. Therefore, it makes closer stars appear to shift more, relative to distant ones. |
| How do you define the parallax angle of a star? | Half the angle moved against a background of very distant stars in six months. |
| The ________ the parallax angle, the __________ the star. | Greater Closer |
| What is the definition of a parsec (pc)? | The distance to a star with a parallax angle of one second of arc. |
| How much is one second of arc? | 1/3600th of a degree. |
| How do you calculate distance in parsecs? | 1 ---------------------------------------- Parallax angle (sec) |
| Typically, what is the distance between neighbouring stars? | A few parsecs |
| What does the luminosity of a star depend upon? | It's temperature and size |
| What do Cepheid variable stars do? | Pulse in brightness, with a period related to their luminosity. |
| The _______ the period, the _______ the Cepheid. | Longer Brighter |
| How do astronomers estimate the distance to Cepheid variables? | - Find some nearby Cepheids whose distances have been measured accurately. - Measure their brightness and luminosity - Plot a graph of luminosity against period - Measure the observed brightness and period of a Cepheid of interest, and find the luminosity from the graph - Use luminosity and brightness to work out the distance. |
| What did telescopes reveal? | That the Milky Way consists of millions of stars, and that the Sun was a star in the Milky Way galaxy. |
| What else did telescopes reveal? | Fuzzy objects in the night sky, and these were originally called nebulae. |
| What was the main issue in the Curtis-Shapely debate? | Where spiral nebulae objects within the Milky way or separate galaxies outside it? |
| What did Hubble's observations of Cepheid variables conclude? | The Cepheid variables in one nebula indicated that it was much further away than any star in the Milky Way, so he concluded that this nebula was a separate galaxy. |
| What are intergalactic distances typically measured in? | Megaparsecs (Mpc) |
| How do you calculate the speed of recession (km/s) of a distant galaxy? | Hubble Constant (km/s per Mpc) ------------------------------------------------------- Distance (Mpc) |
| How do the motions of galaxies suggest that space itself is expanding? | The further away they are, the faster they are moving. Everything appears to be moving away. |
| How do scientists believe the world began? | With a 'Big Bang' about 14 million years ago. |
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