The Sun

The Sun

The Birth of the Solar System

The Sun is a yellow dwarf star that formed 4.6 billion years ago from a giant rotating interstellar cloud of gas and dust. As this cloud condensed under the pull of gravity, it started to spin and form a disk. The center of this disk formed the Sun and the remaining material formed the planets, moons, and small bodies of our solar system. Composed mostly of hydrogen and helium gas, the Sun accounts for 99.8% of the mass in the solar system.

The Solar Interior

At the core of the Sun, temperatures reach 27 million degrees Fahrenheit and pressures are more than 230 billion times the air pressure at Earth’s sea level. These intense conditions are required for the fusion of hydrogen into helium, which provides most of the energy available in the solar system. Fusion releases high energy photons, which only make it a few millimeters before they are absorbed and re-radiated by the densely packed atoms in the core, losing energy as they go. It can take 170,000 years for a photon to reach the surface of the Sun and escape into space!

The Solar Atmosphere

Researchers at the University of Arizona have made significant contributions to the study of the sun and to space physics. LPL Research Scientist Dr. Marcia Neugebauer conducted revolutionary measurements of the solar wind and its properties. LPL Professors Joe Giacalone and Kristopher Klein are instrument team members on the Parker Solar Probe, which came closer to the Sun than any previous spacecraft. The Parker Solar Probe will help us understand how the Sun’s atmosphere is heated and how energetic particles from the Sun are accelerated into the solar system.


MASS: 1.9x10^30 kg about 318,000 times Earth
DIAMETER: 1.4 million km about 109 Earth Diameters
SURFACE GRAVITY: 274 m/s2 about 28 times Earth
Illustration of the Sun with sunspots. A blown out portion shows the Sun's Core, Radiative Zone and Convection Zone (in order going outward). A cartoon of Hydrogen fusing into Helium is shown at bottom and the Parker Solar Probe at top.