Although it’s a dwarf, compared to the Earth, the sun is huge. You would need to line up 109 Earths, side by side to equal the Suns diameter. It has the mass of 330,000 Earths.
It formed from a molecular cloud that collapsed under gravity, into a nearly perfect sphere, made of hot plasma.
It contains 99.86% of the mass of entire Solar System. The rest of the stuff flattened into a disk that formed the planets.
The center became so hot and dense that it initiated nuclear fusion.
It’s 73% hydrogen and 23% helium. The rest is a mix of heavier elements like carbon, oxygen, and iron, stuff that people are made of.
Those heavy elements in the sun actually make it a Population 1 star, heavy element rich. The abundance of heavy elements in the solar system suggest that a nearby super nova might have had influence.
Today the Sun is middle-aged, having changed very little in the past Four billion years, and shouldn’t change much for the next five billion.
After that, the hydrogen that fuels the sun will run out. When that happens, the Sun’s core will become smaller and denser, while the outer shell grows.
It’s expected to become a red giant as big as Earth’s orbit around it.
Some cultures see the Sun as a god. The calendar most widely used today is a solar one.
The first day of the week is Sunday, followed by the Moon day, Monday.
The name sun has a Latin root, sol. Today, sol is used to describe 1 solar day. On Earth, that’s 24 hours. On Mars, that’s 24 hours and 39 minutes.
The Sun is brighter than 85% of the stars in the Milky Way Galaxy, which are mostly red dwarfs.
The next brightest star in the sky next to the Sun is the star Sirius, 8.6 light years away.
The Earth is about 150 million Km away from the Sun, 93 million miles.
The distance does vary throughout the year as Earth’s orbit is elliptical. The Earth is closest in January. This is called the perihelion. It’s furthest in July, known as the aphelion.
The light from the sun, traveling at 300 thousand Km/s takes 8 minutes and 17 seconds to reach Earth on average
The Sun drives almost all the life on Earth through photosynthesis, and is responsible for Earth’s climate and weather.
The Sun rotates once every 25.6 days at the equator, 33.5 at the poles.
Since Earth is also in orbit around the sun it appears to rotate once every 28 days.
The Sun hits Earth with 1,368 Watts of energy per square meter. Earth’s atmosphere does stop some of it from reaching the ground. So what makes it to the surface is more like 1,000 watts per square meter. That’s in clear skies where the Sun is directly overhead.
When high in the sky, or from space, the sun is actually white. If anything it has a greenish tinge.
As it gets closer to the horizon, it goes through a variety of colours, from yellow, red, orange and magenta.
The surface of the Sun’s is 5,778 K, 5,505 degrees Celsius (9,941 degrees Fahrenheit).
The deeper we go, the hotter it gets, as nuclear fusion turns the hydrogen fuel into helium. That helium core is 150 times denser than water. The core is somewhere between 20-25 % of the solar radius. It’s 15.7 million Kelvin.
Data from NASA’s Solar and Heliospheric Observatory SOHO spacecraft is suggesting that the core is spinning faster than the outer radiative zone.
99% of the Sun’s energy is produced at between 25 and 29% of the Sun’s radius. The rest of the Sun get’s heated layer by layer, until it travels to the solar photosphere, where it’s released into space as sunlight and energetic particles.
The Sun releases 4.26 million metric tonnes of energy into space every second.
The sun has an atmosphere too. The chromosphere, the transition zone, the corona, and the heliosphere.
The coolest layer of the Sun at 4,100K is just above the surface, extending 500 Km above the photosphere.
The chromosphere, the transition zone, the corona, and the heliosphere above that are much hotter however.
The temperature in the 2,000 KM thick chromosphere gradually increases to 20,000 K.
In the thin 200 Km transition layer, the temperature rises quickly from the chromospheres 20,000 K to 1 Million K.
The next layer is the corona. The temperature here averages 1 to 2 million K, but some areas are in the 8-20 million range.
The outermost atmosphere is the heliosphere. This turbulent layer carries the solar wind, creating the solar magnetic field into a spiral shape fired out into space until it hits the heliopause 50 AUs out, creating a termination shock.
This creates a bubble around the entire solar system, the size of which is well beyond Pluto, protecting against outside pressure.
The Voyager 1 spacecraft has actually passed through the shock in 2012. It could tell because there was a sudden 4000 % increase in plasma density.
Oddly enough we’ve sent spacecraft to every planet in the solar system, but not the sun.
Well, that’s about to change.
Next year, NASA plans to send its first robotic mission to the Sun.
This journey to the center of the solar system will help answer some questions.
It’s called Solar Probe Plus. It will orbit the Sun 24 times, 6 million Km away, seven times closer than the Helios spacecraft back in the 70s.
One of the questions is why the Sun’s atmosphere is hotter than the surface of the Sun.
Another is how the Sun sends a stream of charged particles in every direction at over a million KM/hr.
The third question is why the Sun periodically sends dangerous high energy particles, that can hurt astronauts and spacecraft?
An 11.4 cm thick carbon composite shield will help the craft survive the hellish 1,370 C (2,900 F) heat.
It will also have thermal radiators to expel the heat that passes through the shield.
Best of luck Solar Probe Plus.
You’re one hot ride.
Thank you for reading.