# GCSE Physics P7 (OCR) - Mapping the Universe

### Description

GCSE Physics (P7) Flashcards on GCSE Physics P7 (OCR) - Mapping the Universe, created by Josh Price on 24/04/2015.
Flashcards by Josh Price, updated more than 1 year ago
 Created by Josh Price over 8 years ago
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## Resource summary

 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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