Astronomy (Edexcel International A Level Physics)

The 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

Cepheids are a type of standard candle.

Describe how standard candles can be used to determine distances to stars.

The 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.

i) Label the x-axis of the HR diagram. You should include approximate values.

(3)

ii) There are five zones, Z1, Z2, Z3, Z4 and Z5, identified on the HR diagram.

Complete the following table. You should match one zone with each description.

 (3)

*iii) The position of a star on the HR diagram changes as the star evolves.

Explain how a star like the Sun evolves as it progresses from zone Z3 to its final position on the HR diagram.

(6)

Sirius 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 = ......................................

In 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.

An 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.

i) Show that the luminosity of the source is about 2 × 10³⁵ W.

(4)

ii) 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)