Big blue marble or pale blue dot, Earth revolves around the sun once while rotating 365 1/4 times.
Earth is titled 23 1/2 degrees to the plane of its axis, and this causes the seasons. When the Northern Hemisphere tilts toward the sun, we have summer. When it tilts away from the sun, we have winter.
Our atmosphere is 21% oxygen and 78% nitrogen. It has carbon dioxide and water vapor. It provides a stable temperature and protects us from harmful rays. Plants create oxygen by photosynthesis.
The sun causes air to expand and move. Wind is air in motion. Clouds are droplets of water which turn into rain. Water evaporates to form clouds.
Water covers 70% of our planet. If the earth were closer to or further away from the sun, liquid water could not exist. Water shapes the earth's crust, the Grand Canyon being an example. There is an ocean at the North Pole and an ice cap at the South Pole. Earth has a magnetic field because of its iron core.
The chromosphere lies between the photosphere (surface) and the corona . It is where prominences originate. Prominences are jets of plasma (ionized gas).
The sun does not burn the way we think of something burning. Electrons change when wood burns. Elements change when nuclear fusion occurs.
Eclipses occur when the earth, moon & sun line up. Both the earth and the moon cast shadows into space. Solar eclipses occur when the moon's shadow falls on the earth. Lunar eclipses occur when the earth's shadow falls on the moon. Lunar eclipses are visible everywhere on the night side of our planet.
Earth rotates into and out of its own shadow. This produces the illusion of the sun setting and rising. The sun is stationary relative to the earth. The rotating earth makes the sun only appear to rise and set.
Earth's shadow is always there, and different parts of our planet spin into it during a 24 hour period. Half of the earth always faces its shadow. Half always faces the sun. What we call night is our planet's shadow.
Moonlight is sunlight reflected by the moon. Every spot on the moon is in the moon's shadow 2 weeks each month.
Half of the celestial sphere is visible everywhere on the earth. The earth blocks the other half. Celestial objects appear to move in curves as the earth rotates.
Light is radiation from space. Stars emit both visible and invisible light. The Hubble Space Telescope studies visible light. Radio waves, microwaves, infrared, ultraviolet, X-rays & gamma rays are invisible light.
Hubble, Spitzer, Chandra & Compton comprised NASA's Great Observatories Program. Spitzer studied infrared, Chandra studied X-Rays & Compton studied gamma rays. These telescopes imaged objects across the electromagnetic spectrum.
The Very Large Array is a radio observatory in New Mexico. Dishes receive radio waves, which have the longest wavelengths.
The Allen Telescope Array is used by SETI to detect signals from extraterrestrials. It is in the Cascade Mountains of California.
BLACK HOLE NOTES
Black holes are massive stars that have collapsed under their own gravity. Astronomers like to say that even light cannot escape. Nothing travels faster than light at 186,000 miles a second, and the escape velocity of a black hole exceeds that. The escape velocity on earth is 25,000 miles an hour. A massive star's collapse is so drastic that only a gravitational field remains. With gravity this powerful, time slows and ultimately stops. At the center of a black hole is a singularity, a sizeless point of infinite density. The star's mass disappears into the singularity and becomes a bottomless funnel.
Cygnus X-1 is a black hole. An X-ray telescope found it . Black holes are at the centers of galaxies and may have caused their formation.