Ancient civilizations knew about the sun: Sumerians, Babylonians, Egyptians & Greeks. The Greeks knew the most. Aristarchus knew that 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 concept.
Einstein understood 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, fusing hydrogen to create helium.
The sun influences everything on earth. Its nuclear fire is the source of life. No wonder the ancients worshiped it! To them, the sun was a god!
The sun and the earth are intertwined. The sun causes the Northern Lights when the solar wind hits the top of our atmosphere. Variations in the sun's output cause climate change.
Galileo observed sunspots in 1610. They appear dark because they are cooler than their surroundings. Sunspots are caused by the sun's magnetic field.
The sun helps us and hurts us. Sunlight causes photosynthesis. It makes vitamin D. We see objects because they reflect sunlight. The sun also causes burns and can 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. Rays from the corona stream into space. Sunlight takes 8 minutes to reach Earth.
The sun formed 4.6 billion years ago from a nebula of hydrogen gas. Gravity caused the nebula to shrink and spin. It heated up and became a sphere. Stars and planets become spheres because spheres have the smallest surface areas of any geometrical shape. All their parts are the same distance from the center. Heat is "atoms in motion," and elements in the sun fuse to produce 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 blood 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 & gamma rays.
1 Radio waves - Long wavelengths used by radio telescopes. No sound!
2 Microwaves - Used in microwave ovens and cell phones.
3 Infrared - Infrared rays are not heat. They cause heat, heat being atoms in motion. 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
The sun plays a role in eclipses. A solar eclipse takes place when the moon passes between the earth and the sun. This happens during new moon. I saw the Great American Eclipse on August 21, 2017. There will be another one on April 8, 2024. Any location averages a solar eclipse every 375 years. It is rare that Kentucky and Tennessee are getting 2 this close.
The sun and moon appear to be the same size because the sun is 400 times larger than the moon and 400 times farther away. These are the only disks we can see with the naked eye. A billion years ago, the moon was closer to Earth and appeared larger. A billion years in the future, it will be farther away and too small to cover the sun. The age of solar eclipses will be over! As far as we know, ours is the only phenomenon of this kind in the universe. People gaze in awe as the sun and moon line up with the spot they stand on.
5 billion years hence, the sun will be a red giant, expanding beyond Earth's orbit as life comes to an end. The sun 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 and finally a black dwarf.
THE SUN'S HEARTBEAT: AND OTHER STORIES FROM THE LIFE OF THE STAR THAT POWERS OUR PLANET by Bob Berman
I reviewed Bob Berman's book for Amazon.
Berman is my favorite astronomer. We are close to the same age, and that makes his observations and writing style accessible. He injects his extensive knowledge of the sun with humor. Certain topics stand out, like the 7 classes of stars based on temperature, size & color. These are O B A F G K M stars, remembered by "Oh Be A Fine Girl Kiss Me." The lettering is arbitrary, but O and B stars are blue, massive & hot. Yellow and orange stars like the sun are average. Our sun is a G. 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 tells us that the sun is a metal-rich third generation star.
Berman praises the Greeks. They were scientists! Aristarchus knew that the earth orbited the sun, and Eratosthenes determined the size of the earth. Hipparchus divided stars into 6 magnitudes, a system still used today. Heracleides Ponticus knew Venus orbited the sun, and Anaxagoras knew the moon reflected sunlight.
To Berman, Aristotle and Ptolemy were villains. Their erroneous ideas held sway and stifled science until Copernicus 14 centuries later.
I wrestled with images of a tilting Earth orbiting the sun. Our seasons are caused by this tilt. Earth is 91.5 million miles from the sun on January 3, and 94 million miles from it on July 4. The Northern Hemisphere experiences summer when it is fartherest 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 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 and 400 times farther away, making the 2 disks appear the same size. It is like putting a quarter on top of a quarter. During totality, the sun, moon & the spot we stand on form a straight line. We see the corona!
Everything on earth came from the sun, including the earth itself, which formed from debris left over when the sun formed. All our energy comes from the sun. Coal, oil & wood are stored sunlight. All life depends on the sun. Evolution is sun-driven as species mutate into new ones.