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Astronomy

Hubble's law

  • 3 things to know
  • Unit AS 2

Overview

Hubble's law, defining each symbol with its unit and value of the Hubble constant with its unit.

What you need to know

Answer each one before you reveal it.

Your recallNot started
Numbers

A galaxy has a red shift parameter of 0.030. Calculate its distance, taking the Hubble constant as 2.4 × 10⁻¹⁸ s⁻¹.

Key term

Why must the distance to a galaxy be found by a method independent of its red shift?

Key term

State Hubble's law, defining each symbol with its unit.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    State Hubble's law, defining each symbol with its unit.

    Model answer

    v = H₀d, where v is the speed of recession of a galaxy in m s⁻¹, H₀ is the Hubble constant in s⁻¹ and d is the distance to the galaxy in metres.

  2. 2

    State the value of the Hubble constant with its unit.

    Model answer

    The Hubble constant is approximately 2.4 × 10⁻¹⁸ s⁻¹.

  3. 3

    Why is the unit of the Hubble constant s⁻¹?

    Model answer

    Because it is a speed divided by a distance, and m s⁻¹ divided by m leaves s⁻¹.

  4. 4

    What is the shape of a graph of recession speed against distance for distant galaxies, and what does its gradient give?

    Model answer

    It is a straight line through the origin, and its gradient is the Hubble constant.

  5. 5

    A galaxy recedes at 3.70 × 10⁶ m s⁻¹. Calculate its distance, taking the Hubble constant as 2.4 × 10⁻¹⁸ s⁻¹.

    Model answer

    d = v/H₀ = 3.70 × 10⁶ / 2.4 × 10⁻¹⁸ = 1.5 × 10²⁴ m, and 2.4 × 10⁻¹⁸ × 1.54 × 10²⁴ returns 3.70 × 10⁶ m s⁻¹ as given.

  6. 6

    A galaxy recedes at 6.40 × 10⁶ m s⁻¹. Calculate its distance, taking the Hubble constant as 2.4 × 10⁻¹⁸ s⁻¹.

    Model answer

    d = v/H₀ = 6.40 × 10⁶ / 2.4 × 10⁻¹⁸ = 2.7 × 10²⁴ m, and 2.4 × 10⁻¹⁸ × 2.67 × 10²⁴ returns 6.40 × 10⁶ m s⁻¹.

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