Every second, 149.6 million kilometers away, a colossal ball of plasma converts hydrogen into helium and quietly makes every form of life on Earth possible. Here’s a rundown of the numbers behind our star.

The basics

The Sun is a G-type main sequence star (G2V), sitting at the center of the Solar System, about 4.6 billion years old. Its diameter of roughly 1,391,400 km makes it about 109 times wider than Earth, and its mass, 1.989 × 10³⁰ kg, accounts for over 99.8% of all the mass in the Solar System. Despite that bulk, it’s not especially dense: about 1.41 g/cm³, only 1.4 times the density of water, since it’s made almost entirely of hydrogen and helium gas rather than rock or metal.

Composition by mass breaks down to roughly 73.8% hydrogen, 24.9% helium, and about 1.3% heavier elements, oxygen, carbon, neon, iron, and others. And because the Sun is a giant ball of plasma rather than a solid, it doesn’t rotate as one piece: the equator spins around once every ~25 days, while the poles take closer to 35.

Hot at the surface, unbelievably hotter at the core

The visible surface, the photosphere, sits at around 5,500-5,800 °C. That’s already hard to picture, but it’s nothing next to the core, where temperatures reach roughly 15 million °C. That heat and pressure are exactly what’s needed to sustain nuclear fusion: hydrogen nuclei fusing into helium, releasing the energy that eventually reaches us as sunlight. Because that energy has to work its way out from the core through the radiative and convective zones before radiating from the photosphere, light generated in the core today won’t reach the surface for tens of thousands to a few hundred thousand years, even though, once it does escape, it only takes about 8 minutes and 20 seconds to cross the 149.6 million km to Earth.

Sunspots and the 11-year cycle

Sunspots are cooler, darker patches on the photosphere caused by intense localized magnetic activity. Their number rises and falls on an ~11-year rhythm known as the solar cycle, moving between a quiet “solar minimum” and an active “solar maximum.” More sunspots generally means more solar flares and coronal mass ejections, bursts of charged particles that stream outward as solar wind, typically moving at 300-800 km/s.

Why it matters here on Earth

Beyond providing the light and warmth that make life possible, the Sun drives Earth’s weather, climate, and ocean currents. Its activity can also disrupt satellites, GPS, and radio communications, and when solar particles interact with Earth’s magnetic field, the result is the aurora.

A few numbers worth sitting with

  • The Sun produces enough energy in one second to power all of Earth’s energy needs for about 27 million years.
  • If the Sun were hollow, more than a million Earths could fit inside it.
  • The Sun is a nearly perfect sphere, a direct consequence of its own gravity.
  • In about 5 billion years, the Sun will expand into a red giant before eventually shedding its outer layers and leaving behind a white dwarf.

Sources:
NASA Solar System Exploration – In Depth: Sun
NASA NSSDCA – Sun Fact Sheet