Big blue marble or pale blue dot, Earth revolves around the sun once while rotating 365 1/4 times.
Earth's axis is titled 23 1/2 degrees, 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 contains water vapor and carbon dioxide. It provides a stable temperature and protects us from harmful rays. Plants create oxygen by photosynthesis.
Clouds are tiny drops of water that turn into rain. Water evaporates to form clouds. The sun causes air to expand and move. Wind! Weather satellites track hurricanes.
Water covers 70% of out planet. If the earth were closer to or farther away from the sun, liquid water would not exist. Water shapes the earth's crust, and the Grand Canyon is 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 is 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. When wood burns, electrons change. When nuclear fusion occurs, elements change.
Earth is fartherest from the sun in summer. The Northern Hemisphere tilts toward the sun. Earth is closest to the sun in winter. The Northern Hemisphere tilts away from the sun. Earth's axis always points in the same direction.
Eclipses occur when the sun, moon & earth line up. Both the moon and the earth throw 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 Earth.
Sunrises, sunsets & moonlight are illusions. Sunrises and sunsets are caused by the spinning, turning & rotating earth. Moonlight is sunlight reflected by the moon.
Earth rotates out of and into its own shadow to produce the illusion of the sun rising and setting. The sun is stationary relative to the earth. The rotating earth makes the sun appear to rise and set. What we call night is Earth's shadow.
Earth's shadow is always there, and different parts of our planet spin into it over a 24 hour period. Half of the earth always faces the sun. Half always faces the shadow. Every place on the moon spends 2 weeks in the moon's shadow each month.
Half of the celestial sphere is visible everywhere on earth. Earth itself blocks the other half. Celestial objects appear to move in curves as the earth rotates.
Light is radiation traveling through space. Stars emit both visible and invisible light. Radio waves, microwaves, infrared, ultraviolet, X-rays & gamma rays are invisible. The Hubble Space Telescope studied visible light.
Hubble, Spitzer, Chandra & Compton made up NASA's Great Observatories Program. Spitzer studied infrared, Chandra studied X-Rays & Compton studied gamma rays. These 4 telescopes imaged objects across the electromagnetic spectrum.
The Very Large Array is a radio observatory in New Mexico. Dishes receive radio waves. Radio waves have the longest wavelengths. No sound!
BLACK HOLE NOTES
Black holes are massive stars that have collapsed under their own gravity. Astronomers enjoy saying 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. Astronomers found it using an X-ray telescope. Black holes are at the centers of galaxies and may have caused their formation.