Ancient civilizations worshipped the sun: Sumerians, Babylonians, Egyptians & Greeks. The Greeks had science. Aristarchus knew the sun was the center of the solar system and that the earth revolved around it. Copernicus' heliocentrism was a revival of an ancient Greek idea.
Einstein knew that energy and matter are the same thing. Nature stores energy in matter, and when the sun converts it to energy, heat and light are given off. The sun shines by nuclear fusion, combining hydrogen atoms to make helium.
The sun influences everything on earth. Its nuclear fire is the source of life. To the ancients, the sun was a god!
The sun and the earth are connected. The sun causes the Northern Lights when the solar wind hits the top of our atmosphere.
Galileo saw sunspots. They are caused by the sun's magnetic field. They appear dark because they are cooler than their surroundings.
The sun helps us and hurts us. Sunlight causes photosynthesis. It makes vitamin D. We see objects because they reflect sunlight. The sun can cause burns and fry our retinas if we are not careful.
The sun is 93 million miles away, a distance known as an astronomical unit (AU). The temperature at the sun's core is 30 million degrees. Its surface temperature is 11,000 degrees.
The photosphere is the sun's surface. The corona is its atmosphere, seen during a total eclipse. Sunlight takes 8 minutes to reach the earth.
The sun formed 4.6 billion years ago in a nebula of hydrogen gas. Gravity caused the gas to shrink and spin. It heated up and became a globe. Stars and planets become globes because globes have the smallest surface areas of any geometrical shape. All the parts are the same distance from the center. Heat is "atoms in motion," and elements in the sun fuse and give off energy. Fusion depends on there being enough mass to get it started.
When a star's hydrogen is gone, it burns helium to make carbon and oxygen. When a star tries to make iron, it goes supernova, spewing elements into space. The extreme temperature fuses the heavier elements. There are 92 natural elements. Bottom line: Elements are created inside stars. The iron in our bodies came from supernova explosions.
The sun emits different kinds of radiation. The electromagnetic spectrum moves from radio waves to microwaves to infrared to visible light to ultraviolet to X-Rays to gamma rays.
1 Radio waves - Long wavelengths received by radio telescopes. There is no sound.
2 Microwaves - Used in microwave ovens and cell phones.
3 Infrared - Infrared rays cause heat. The James Webb Space Telescope will see infrared light.
4 Visible light - Composed of colors.
5 Ultraviolet - Short, high energy waves. Ultraviolet burns the skin. Our atmosphere protects us.
6 X-Rays - Used in medicine.
7 Gamma rays - From explosions throughout the galaxy.
SPECTRUM OF VISIBLE LIGHT
A solar eclipse occurs when the moon passes between the earth and the sun. This happens at new moon. I saw the Great American Eclipse, August 21, 2017. There will be a second one, April 8, 2024. Any location averages a solar eclipse every 375 years.
The sun and moon appear to be the same size because the sun is 400 times larger than the moon but 400 times further away. These are the only disks we can see with the naked eye. A billion years ago, the moon was closer to the earth and appeared larger. A billion years in the future, it will be too far away and too small to cover the sun. The age of solar eclipses will be over. Ours is the only phenomenon of this kind in the universe as far as we know. People gaze in awe as the sun and moon line up with the spot they stand on.
The sun was born in a gaseous cloud with hundreds or thousands of other stars. It stands alone because its siblings dispersed over time.
5 billion years hence, the sun will be a red giant, expanding beyond Earth's orbit as all life comes to an end. It will give off a cloud of gas like the Ring Nebula, the dying star in Lyra. Its core will shrink to become a white dwarf.
THE SUN'S HEARTBEAT: AND OTHER STORIES FROM THE LIFE OF THE STAR THAT POWERS OUR PLANET by Bob Berman
Berman is my favorite astronomer. We are almost the same age, which makes his observations and writing style accessible. He injects humor into his knowledge of the sun. Certain topics stand out like the 7 classes of stars based on size, temperature & color. These are O B A F G K M stars, remembered by "Oh Be A Fine Girl Kiss Me." The letters are arbitrary, but O and B stars are blue, massive & hot. Yellow and orange stars like the sun are average. The sun is a G star. M stars on the right are red dwarfs, small and cool. Cool, that is, as far as stars go. There are more red dwarfs than any other kind of star. To their right are brown dwarfs, objects whose mass and temperatures are not sufficient for nuclear fusion to begin. Berman calls the sun a metal-rich third generation star.
Berman praises the Greeks. They had science! Aristarchus knew the earth orbits the sun, and Eratosthenes determined the size of the earth. Hipparchus divided stars into 6 magnitudes, a system still used. Heracleides Ponticus knew Venus orbits the sun, and Anaxagoras knew the moon reflects sunlight.
To Berman, Aristotle and Ptolemy were villains. They stifled science for 14 centuries until Copernicus.
I wrestled with images of a tilted Earth orbiting the sun. The tilt causes our seasons. Earth is 91 million miles from the sun on January 3, and 94 million miles from it on July 4. The Northern Hemisphere has summer when it is furtherest from the sun.
We circle the sun 67,000 miles an hour, but feel like we are not moving. We know we are because the sun changes its position against the background stars. Its yearly path is called the ecliptic because it is where eclipses take place.
Chapter 16 deals with totality, and Berman regards solar eclipses as impossible coincidences. Totality happens because the sun is 400 times larger than the moon but 400 times further away, making the 2 disks appear the same size. During totality, the sun, moon & the spot we stand on form a straight line.
Everything on earth came from the sun, including the earth itself, which formed from stuff left over when the sun formed. All our energy comes from the sun. Wood, coal & oil are stored sunlight. All life depends on the sun. Evolution is sun-driven as species mutate into new ones.