The Sun - Key Facts About Our Closest Star
Posted 12th Feb 2020
Introducing Our Sun
The Sun is an average yellow dwarf star that lies at the heart of our Solar System. It is the engine that drives the orbits and dynamics of the planets, and gives warmth and life to planet Earth.
It is an enormous ball of hot plasma gas that is powered by nuclear fusion in its core. For 4.6 billion years, the Sun has been fusing hydrogen into helium, releasing huge amounts of energy in the process that causes the Sun to shine.
Leftover debris from the Sun’s formation collapsed under gravity to form the 8 planets as well as the countless dwarf planets, asteroids, and comets that continue to orbit the Sun.
The Sun is about halfway through its 10 billion year lifetime. In 5 billion years, the Sun will run out of hydrogen fuel and will begin to die, eventually puffing off its outer layers of gas into a planetary nebula while the core collapses into a white dwarf.
The Sun is a typical star, similar to hundreds of billions of stars in our Milky Way galaxy, and among the trillions of other stars throughout the universe. Stars are the building blocks of all galaxies, and the powerhouses of countless other solar systems.
Size: The Sun is a ball of burning plasma 1.4 million kilometres in diameter. Compared to the Earth, 1.3 million Earths could fit inside the Sun.
Gravity: The Sun has a mass of 1.9 × 1030 kilograms or 333,000 times heavier than Earth. It contains 99.8% of all the mass in the Solar System. If you could stand on the surface of the Sun (not recommended!), gravity would be 28 times stronger than on Earth.
Age: The Sun is 4.6 billion years old, and is about halfway through its 10 billion year lifetime.
Distance from Earth: The Sun is 150 million kilometres from Earth. It takes light 8 minutes to travel from the Sun to Earth.
Composition: The Sun is a ball of hot plasma gas that burns hydrogen into helium in a process called nuclear fusion. The Sun is made of 73% hydrogen, 25% helium, and trace amounts of heavier elements such as oxygen, carbon, neon, and iron.
Star type: The Sun is an average yellow dwarf star (or in astronomer-speak: a G-type main-sequence star).
Temperature: The Sun’s surface (or photosphere) is about 5,500 degrees Celsius. For reasons we don’t yet understand, the atmosphere above the surface (the corona) is much hotter, around 1 million degrees Celsius.
Rotation: The Sun’s surface is a fluid plasma and rotates at different speeds. On the equator, the surface rotates once every 25 days while near the poles, the surface moves slower and takes 35 dates to rotate.
Speed: The Sun moves at 220 kilometres per second around our Milky Way galaxy.
Moons: The Sun has 0 moons, but it has many other satellites including 8 planets, at least 5 dwarf planets, and countless asteroids and comets that orbit the Sun.
Discovered by: Ancient humans! The Sun has been observed, worshipped, and studied for all of human history, but we are still unravelling its mysteries.
Timeline of Solar Science - before space missions
Long before telescopes, humans have kept an eye on the Sun. They studied its movements, predicted its eclipses, and speculated on its place in the Solar System.
Here’s a brief history of key solar discoveries, pre-space race.
1375 BCE: Babylonians used stone tablets to record solar eclipses.
800 BCE: Astronomers in ancient China recorded the first observations of sunspots in I Ching, the Book of Changes.
1600s: Galileo used a telescope to observe the cosmos. Around 1610, he began to track mysterious dark spots on the Sun.
1842: During an eclipse over Italy, English astronomer Francis Baily suggested that the mysterious haze encircling the Sun — known as the corona — is the Sun’s atmosphere.
1859: English astronomer Richard Carrington observed a sudden brightening on the Sun’s surface through his telescope. Seventeen hours later, strong aurora are seen as far south as Cuba and telegraph systems across the western world fail and catch fire. This Carrington Event was the first link between a coronal mass ejection on the Sun and a geomagnetic storm on Earth.
1908: American astronomer George Ellery Hale and colleagues discovered the solar cycle, whereby the number of sunspots varies over an 11 year cycle.
1942: Discovery that the corona is millions of degrees Celsius, due to observations of iron spectra with 13 missing electrons. This coronal heating problem, where the solar atmosphere is so much hotter than its surface, is still an open question.
1946: High energy particles detected on Earth were first linked with the Sun (and a recent flare), confirming the concept of a solar wind.
Sun missions - past and present
Since the dawn of the space race, many missions have focused on the Sun. Here is a sampling of some of the key solar missions, past and present.
Skylark – 1961 – This British sounding rocket carried up an X-ray instrument from the University of Leicester, and captured the first X-ray image of the Sun’s corona. Skylark rockets continued to carry instruments to study the Sun for decades to come.
Ariel 1 – 1962 – The first British satellite was primarily focused on studying the Sun and its interaction with our atmosphere.
OSO – 1962-1975 – NASA launched 8 identical OSO missions over 12 years in order to fully study the 11-year cycle of the Sun. The spacecraft measured the Sun in UV, X-rays, and gamma rays. X-ray instruments built by the University of Leicester flew on two of these missions, OSO-4 and OSO-5. A flight spare of OSO can be seen at the National Space Centre.
Ulysses – 1990 – This ESA-NASA mission studied the solar wind and the heliosphere that encompasses our Solar System. It was the first mission to fly over the poles of the Sun. Although it did not carry cameras to image the poles, its instruments sampled the plasma and magnetic field streaming from the Sun for 18 years.
SOHO – 1995 – Another ESA-NASA collaboration, SOHO has studied the Sun from the L1 point between the Earth and the Sun for more than 20 years, and for two full cycles of solar activity.
STEREO – 2006 – Two twin spacecraft, A and B, that orbited the Sun just in front and behind the Earth, in order to capture a 3D picture of the Sun’s activity.
SDO – 2010 – An ongoing solar workhorse that captures images of solar flares and the sources of these eruptions.
Parker Solar Probe – 2018 – This NASA mission is “touching” the Sun by flying closer than we’ve ever been to the Sun and sampling the million degree temperatures of the corona in order to understand how the solar wind is created.
Solar Orbiter – 2020 – This ESA-NASA mission will arrive at the Sun in 2022 and capture the first ever images of the Sun’s poles. It will be able to orbit in sync with sunspots and evolving flares, helping us to better understand and predict solar storms that could damage the Earth.
Visit https://spacecentre.co.uk/blog-post/introducing-our-sun/ to read about what we still don't know about The Sun and more information on our nearest star.