Physics

23.1 - The Solar System

2 min

note 1 of 3

The Sun, our star

The Sun is a medium-sized star, made up mostly of hydrogen and helium.
It radiates energy across the electromagnetic spectrum, mostly as infrared, visible light, and ultraviolet.
The Sun contains most of the mass of the Solar System, so its gravitational pull dominates, keeping the planets and other bodies in orbit around it.

note 2 of 3

Light-travel time across the Solar System

Distances in the Solar System are so large that it's useful to measure them by how long light takes to cross them.
Light travels at a speed of about 3 × 10⁸ m/s.

Formula for light-travel time

$t = \frac{d}{c}$

Where:

$t$ = Time, in seconds (s)
$d$ = Distance, in metres (m)
$c$ = Speed of light, about 3 × 10⁸ m/s

note 3 of 3

Worked example - Light from the Sun to the Earth

The Earth is about 1.5 × 10¹¹ m from the Sun. How long does light take to travel from the Sun to the Earth?

Step 1 - Formula

$t = \frac{d}{c}$

Step 2 - Substitution and calculation

$t = \frac{1.5 \times 10^{11}}{3 \times 10^{8}} = 500 s$

Step 3 - Interpretation

Light from the Sun reaches the Earth in about 500 seconds, which is roughly 8 minutes.

end of notes

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23.2 - OrbitsNext up

The Sun, our star

The Sun is a medium-sized star, made up mostly of hydrogen and helium.

It radiates energy across the electromagnetic spectrum, mostly as infrared, visible light, and ultraviolet.

The Sun contains most of the mass of the Solar System, so its gravitational pull dominates, keeping the planets and other bodies in orbit around it.

Worked example - Light from the Sun to the Earth

The Earth is about 1.5 × 10¹¹ m from the Sun. How long does light take to travel from the Sun to the Earth?

Step 1 - Formula

$t = \frac{d}{c}$

Step 2 - Substitution and calculation

$t = \frac{1.5 \times 10^{11}}{3 \times 10^{8}} = 500 s$

Step 3 - Interpretation

Light from the Sun reaches the Earth in about 500 seconds, which is roughly 8 minutes.