The Sun

The Heart of the Solar System

At the heart of the solar system lies the Sun, the largest object and a massive star that has a gravitational pull so strong that it holds planets in a rotating orbit around it. Although the Sun is easily visible with the naked eye, it is actually 93 million miles (148.4 million km) away from Earth. This distance is so vast that if the Sun were to suddenly burn out, we would not know about it for 8 minutes.

The Sun. Credit: ESA/NASA

But don’t let the distance fool you. The Sun accounts for approximately 99% of the mass in the solar system, meaning that if you were to combine the mass of every planet, moon, comet, and asteroid, the Sun would be 99 times more massive. With a diameter of 864,938 miles (1.392 million km), it’s also 110 times wider than Earth, and over a million Earths could fit inside of it. This enormous mass creates a powerful gravitational pull that keeps all other matter in orbit around the Sun, rather than floating off into space like a balloon whose string has slipped out of your hands.

Size comparison of the Sun and the planets

The Sun was formed approximately 4.6 billion years ago from a cloud of gas and dust called a nebula. As gravity pulled the particles together, the cloud began to spin and flatten into a disk. The center of the disk became denser and hotter, eventually reaching a temperature of about 15 million degrees Celsius (27 million degrees Fahrenheit). At this temperature, nuclear fusion began, and the Sun was born.

The Sun is currently in the middle of its life cycle, and it will continue to shine for another 5 billion years or so. However, eventually, the Sun will run out of fuel and begin to die. As it does, it will expand into a red giant, swallowing up Mercury and Venus. Then, the outer layers of the Sun will be shed, leaving behind a small, dense core known as a white dwarf.

The structure of the Sun

The life cycle of the Sun

Beautiful and massive as it may be, the Sun also plays an absolutely essential role in our lives, and without it, there would be no life on planet Earth as we know it. It provides energy for plants to grow through photosynthesis, which in turn provides food for animals. The Sun also helps to regulate the Earth's climate and weather patterns. Without the Sun, Earth would be a frozen, lifeless planet.

And while the Sun is vital to life on Earth, life on the surface of the Sun is out of the question. The Sun is a giant ball of gas composed of 71% hydrogen and 27% helium that burns at tens of millions of degrees at its core. It is quite literally a great ball of fire, and the surface is made of a turbulent sea of burning gases. Every second, the Sun converts millions of tons of matter into energy. That accounts for more energy than all the energy ever made by mankind. This energy production is responsible for the light and heat that we feel millions of miles away every time we step out our front doors.

Taken by Hinode’s Solar Optical Telescope on 12 January 2007, this image of the Sun reveals the filamentary nature of the plasma connecting regions of different magnetic polarity.

A solar prominence erupts in August 2012, as captured by SDO

Because the Sun is visible from Earth and has played such a pivotal role in human life since the dawn of time, there is no one story of its discovery. Ancient civilizations both worshipped and feared this ball of light, and solar deities can be found throughout most of recorded history, from the Aztecs and Buddhists to ancient Egyptians and Romans. However, around 450 BC, a Greek philosopher named Anaxagoras first suggested that the Sun was in fact a star, and Galileo Galilei is credited with discovering that the Sun is marked with sunspots (dark areas of irregular shapes on the surface of the Sun).


"The Sun, with all those planets revolving around it and dependent upon it, can still ripen a bunch of grapes as if it had nothing else in the Universe to do." – Galileo Galilei

"The face of the sun is not without expression, but it tells us precious little of what is in its heart." – Armin J. Deutsch

“The sun alone appears, by virtue of his dignity and power, suited for this motive duty (of moving the planets) and worthy to become the home of God himself.” – Johannes Kepler

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