3 marksAstronomers use a variety of techniques to determine the distances to astronomical objects outside our solar system.
Describe how trigonometric parallax can be used to determine the distance to a nearby star.
4 marksExplain how a knowledge of the distances to distant galaxies has enabled astronomers to determine a value for the age of the universe.
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3 marksThe astronomer Hertzsprung used parallax to determine the distances to some of the variable stars known as Cepheids.
Using parallax measurements, astronomers can determine distances to all stars with a parallax angle larger than 2.4 × 10–7 rad.
The variable star Alpha Cephei is 4.6 × 1017 m from the Earth.
Deduce whether the distance to Alpha Cephei could be determined from parallax measurements.
distance from Earth to Sun = 1.5 × 1011 m
3 marksCepheids are a type of standard candle.
Describe how standard candles can be used to determine distances to stars.
12 marksThe Sun is a yellow star with a surface temperature of about 6000 K. In the 20th century, astronomers discovered a large variety of stars in our galaxy.
Hertzsprung and Russell developed the Hertzsprung-Russell (HR) diagram as a way of classifying stars.
An HR diagram is shown below.
(3)
Complete the following table. You should match one zone with each description.
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| Description | Zone |
| High mass hot stars | |
| Low mass cool stars | |
| Low mass hot stars |
Explain how a star like the Sun evolves as it progresses from zone Z3 to its final position on the HR diagram.
(6)
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2 marksSirius is the brightest star in the night sky. The intensity of Sirius is measured to be 1.09 × 10−7 Wm−2.
Calculate the distance of Sirius from the Earth.
luminosity of Sirius = 8.94 × 1027 W
Distance of Sirius from the Earth = .............................................
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1 markIn recent years, astronomers have discovered sources of fast radio bursts (FRBs) in other galaxies. Studies suggest that these sources may be a type of standard candle.
State what is meant by a standard candle.
6 marksAn FRB source emits intense bursts of radio waves, each burst lasting for a fraction of a second. The closest FRB source is in a massive spiral galaxy 4.60 × 1024 m from the Earth.
A detector of area 1.00 × 10−4 m2 on the surface of the Earth received bursts of radio waves. In one burst, 9.40 × 10−23 J of energy was received in a time of 1.15 ms.
When FRB sources were first discovered, some observers suggested that the bursts might be alien communications.
Suggest why this is unlikely.
luminosity of the Sun = 3.8 × 1026 W
(2)
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