1a3 marks
a)
Proxima Centauri is the closest star to Earth.
Fig. 24.1 shows the apparent positions of this star against the background of very distant stars as seen from the Earth over a period of exactly 6 months.
Fig. 24.1
The parallax angle for Proxima Centauri can be determined from Fig. 24.1 using the data provided.
i)
Show that the parallax angle p for Proxima Centauri is about 0.8 arc second.
[1]
ii)
Use your answer in (i) to calculate the distance d of Proxima Centauri from the Earth in light-years (ly).
1 pc = 3.26 ly
d = ........................................ ly [2]
1b4 marks
b)
The galaxies in the Universe may be assumed to be distributed uniformly through space.
In this model, the separation between two neighbouring galaxies is 1.4 × 1023 m and each galaxy occupies a cube of space of volume 2.7 × 1069 m3 as shown in Fig. 24.2.
In this model, the separation between two neighbouring galaxies is 1.4 × 1023 m and each galaxy occupies a cube of space of volume 2.7 × 1069 m3 as shown in Fig. 24.2.
Fig. 24.2
There are on average 1011 stars in each galaxy and the mass of an average star is about 2.0 × 1030 kg.
i)
Estimate the gravitational force between two neighbouring galaxies.
force = ....................................... N [2]
ii)
Show that the mean density of the Universe is about 7 × 10–29 kgm–3.
[1]
iii)
Suggest why the actual mean density of the Universe is different from the value calculated in (ii).
[1]
Did this page help you?
