The Sun

The idea

The Sun is an ordinary star, and essentially every process on Earth’s surface runs on energy it sent us.

Property	Value
Diameter	$1.39\times 10^6\mathrm{km}$ (about 109 Earths across)
Mass	$99.86\%$ of the entire solar system
Surface temperature	About $5500{}^{\circ }\mathrm{C}$
Core temperature	About $15$ million ${}^{\circ }\mathrm{C}$
Distance from Earth	$1.50\times 10^8\mathrm{km}$ = 1 AU
Light travel time to Earth	About 8 minutes 20 seconds

Fusion is the power source

In the core, hydrogen nuclei fuse into helium. The helium weighs slightly less than the hydrogen that made it, and that missing mass becomes energy:

$$E=m{c}^2$$

Because $c^2$ is enormous, a tiny mass difference releases a staggering amount of energy — about $4$ million tonnes of mass per second.

graph LR
    CORE["Core: fusion"] -->|"photons, ~100 000 years"| RAD["Radiative zone"]
    RAD --> CONV["Convective zone"]
    CONV --> PHOTO["Photosphere: light escapes"]
    PHOTO -->|"8 min 20 s"| EARTH["Earth"]

The strangest fact on this page

A photon takes minutes to cross from the Sun to Earth, but can take a hundred thousand years to escape the Sun’s interior — it is absorbed and re-emitted constantly. Sunlight on your face left the core before the last ice age.

Curriculum connection

E2.1

describe the importance of the Sun and its characteristics, including its role in the solar system and in sustaining life on Earth

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E2.2

explain how the Sun’s energy causes natural phenomena on Earth, and how these phenomena contribute to renewable energy production

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