Science Snippet:

Explore The Sun

Sunrise on a December morning. If you enjoy watching sunrises and sunsets, note down the time each day. You might be surprised by when the latest sunset actually is each year.

Our Sun is the closest star; the Earth and all the other planets are in orbit around it. All life on Earth depends on its warmth and light; without it, the Earth would be a frozen wasteland. Let’s learn more about our star and its influence on our solar system.

The Sun is currently 94.4 million miles away. The distances between Earth and the other planets are quite variable. But the distance between the Earth and the Sun stays roughly the same, changing only slightly through the course of each year. Earth (and the other planets) do not orbit the sun in perfectly circular orbits. Instead, the orbits of the planets are slightly oval-shaped (elliptical). Our elliptical orbit makes the distance to the sun vary from 91.4 million miles on January 4 to 94.5 million miles away on July 4. Yes, we are further from the sun in July than in January. But three million miles does not make a lot of difference when the distance you’re dealing with is over 90 million miles. It’s as if you drove the 2800 miles from Washington D.C. to San Francisco but stopped 84 miles before your destination. The trip wouldn’t seem that much shorter.

How far is 94 million miles? Using our travel method from my Venus article, we could cover all the land surface on Earth as well as the Atlantic and Arctic Oceans before we would have traveled 94 million miles. Usually, I’d rather travel in temperate regions than in Arctic ones. But when walking across an ocean, I’d pick the Arctic Ocean in winter when the water would be covered in ice.

The sun through wildfire smoke. This is the sun’s true size in our sky.

In astronomy, we call the size of an object in the sky its angular size. Angular size is measured in degrees. The length across the whole sky is 180 degrees. The sun has an angular size of 0.5 degrees. The moon also has an angular size of 0.5 degrees. The moon looks smaller than the sun but that is because the sun is much brighter. The sun and moon have the same angular size because while the sun’s diameter is 400 times larger than the moon’s diameter, the sun is also 400 times farther away. If a sphere’s diameter increases, its volume increases by a much larger amount. The sun’s volume is so great that 1.3 million Earths could fit inside it. The more massive an object is, the larger its gravitational pull. The sun is 330,000 times more massive than the Earth. In fact, the sun contains 99.8% of all the mass in the solar system. It is not really surprising that the remaining 0.2% of that mass (which makes up all the planets, asteroids, and comets) orbits the sun.

The core of the sun makes up about one-fourth of its total volume, and it is the only part of the sun that produces heat. The heat is produced by the conversion of hydrogen into helium. This process produces enough energy to keep the sun’s core at around 27 million degrees. The heat produced in the core slowly moves through the outer layers of the sun and flows out into space. The layer of the sun immediately above the core is the radiative zone. In this zone, heat is radiated from one atom to the next. The heat moves over very short distances between the atoms. One atom absorbs the heat and starts radiating the heat toward another atom. This atom absorbs the heat and starts radiating heat toward yet another atom. Eventually, the heat radiates all the way into the next layer of the sun, the convective zone. In this layer, heat transfer by radiation does not work. The atoms are not close enough together to radiate heat to one another. Instead, heat is transferred toward the surface by convection. A boiling pot of water is a good example of convection. The water at the bottom of the pot becomes hotter than the water at the top. Hot water is lighter than cold water. This allows the hot water to rise through the cooler water above it. This cooler water moves down into the hot water’s place and becomes heated as well. In the sun, the same type of process occurs. The material nearest to the radiative zone becomes hotter than the material above it. The heated material rises through the cooler material which takes its place. Above the convective zone is the photosphere, the visible surface of the sun, which releases heat and light into space. Although the energy from the core has taken over 100,000 years to reach the sun’s surface, it only takes an additional eight minutes to reach Earth.