What does apparent magnitude (m) measure?

Apparent magnitude measures how bright a star appears from Earth.

What is the Hipparcos scale and why is it significant for apparent magnitude measurements?

The Hipparcos scale is the original magnitude scale, on which the Greek astronomer Hipparcos ranked naked-eye stars from 1 (brightest) to 6 (dimmest); the modern apparent magnitude scale is based on it.

What intensity ratio corresponds to a difference of 1 on the magnitude scale?

A ratio of intensities equal to 2.51.

What intensity ratio corresponds to a difference of 5 magnitudes?

An intensity ratio of exactly 100.

If star A has an apparent magnitude of 2 and star B has an apparent magnitude of 5, which star appears brighter?

Star A appears brighter, because lower apparent magnitude values indicate brighter stars.

AQA A-Level Physics 7408

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Classification by luminosity

2 things to know
Paper 3, section B

Overview

Apparent magnitude as a logarithmic scale, and the intensity ratio between magnitudes.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

How does a magnitude difference relate to an intensity ratio, and why is brightness subjective?

Numbers

Why can apparent magnitude be negative, and what ratio matches five magnitudes?

Questions from this subtopic

Each one with the model answer underneath.

1
What does apparent magnitude (m) measure?
Model answer
Apparent magnitude measures how bright a star appears from Earth.
2
What is the Hipparcos scale and why is it significant for apparent magnitude measurements?
Model answer
The Hipparcos scale is the original magnitude scale, on which the Greek astronomer Hipparcos ranked naked-eye stars from 1 (brightest) to 6 (dimmest); the modern apparent magnitude scale is based on it.
3
What is the apparent magnitude of the dimmest stars visible to the naked eye?
Model answer
Magnitude 6.
4
What intensity ratio corresponds to a difference of 1 on the magnitude scale?
Model answer
A ratio of intensities equal to 2.51.
5
What intensity ratio corresponds to a difference of 5 magnitudes?
Model answer
An intensity ratio of exactly 100.
6
If star A has an apparent magnitude of 2 and star B has an apparent magnitude of 5, which star appears brighter?
Model answer
Star A appears brighter, because lower apparent magnitude values indicate brighter stars.

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