Geocentric System - the Earth is in the center
A first step for flat earthers
Heliocentric System or Copernican Model- the Sun is in the center
Published by Nicolaus Copernicus (1473-1543) in 1543
Galileo Galilei (1564-1642) provided evidence
But Copernicus thought the planets orbited in circles
Johannes Kepler (1571-1630) fixed that
Kepler's Three Laws of Planetary Motion (1609-1619)
1. The Law of Ellipses
Planets revolve in elliptical orbits around the Sun, which is one of the two foci
The point in the orbit when a planet is closest to the Sun is called perihelion
The point in the orbit when a planet is farthest from the Sun is called aphelion
2. The Law of Equal Areas
Imagine an ellipse representing a planetary orbit and a focus representing the Sun
Pick any two points on the ellipse and draw lines from them to the Sun
Color in one of the areas; this has an area
Imagine a second shape, again created with lines to the Sun, with an equal area
A planet travels the elliptical edge of either shape in equal amounts of time
In other words, planets travel faster when they are closer to the Sun
3. The Law of Harmonies
The squares of the orbital periods of planets are directly proportional
to the cubes of the semi-major axes of their orbits
An orbital period is just the amount of time it takes to orbit
The semi-major axis of an orbit, informally speaking, is just the "longest radius"
So all this means is that planets closer to the Sun orbit faster than those farther
But a lot faster, because exponents are involved
Look at exponents!
Mercury year - 88 Earth days
Venus year - 225 Earth days
Earth year - 365 Earth days
Mars year - 687 Earth days
Jupiter year - 4,333 Earth days
Saturn year - 10,758 Earth days
Uranus year - 30,687 Earth days
Neptune year - 60,190 Earth days
The More You Know
The Earth is an "oblate spheroid" and not a perfect sphere
Revolution Facts
1. The Earth's revolution around the Sun is perpetuated by the Sun's gravity
2. The diameter of the Sun (1,392,000 km) is about 109 times that of the Earth (12,742 km)
3. From a bird's-eye view, the revolution travels in a counterclockwise direction
4. Each revolution takes about 365.25 days
5. The Earth is revolving at about 108,000 km/h
6. The Sun's planets revolve in an "ecliptic plane," so all the orbits exist in one plane
Rotation Facts
1. The Earth rotates on an axis
2. The top of the axis is the N Pole and the bottom is the S Pole
The great circle in the middle is the equator (40,075 km)
Everything north of the equator is the northern hemisphere
Everything south of the equator is the southern hemisphere
3. From a side view, the axis is about 22.1-23.5° clockwise of N/S
Notice we are orienting ourselves to the ecliptic plane such that it becomes a line
4. From a bird's-eye view, the Earth rotates in a counterclockwise direction
(But we knew this already because the Sun rises in the east and sets in the west)
5. Each rotation takes 23 hours, 56 minutes, and 4 seconds
6. At the equator, the Earth is moving at about 1,670 km/h
Calendar Facts
1. The summer solstice in the northern hemisphere is the longest day/shortest night
This is the winter solstice in the southern hemisphere
It is June 20 or 21 (first day of summer or winter)
2. The winter solstice in the northern hemisphere is the shortest day/longest night
This is the summer solstice in the southern hemisphere
It is December 21 or 22 (first day of winter or summer)
3. The days that have equal day and night are equinoxes
The northern autumnal equinox is the southern vernal equinox
It is Sep 22-23 (first day of fall or spring)
The northern vernal equinox is the southern autumnal equinox
It is Mar 20-21 (first day of spring or fall)
Longitude Facts
1. I don't like longitudes because they are arbitrary
2. All longitude lines are great circles called meridians
3. Longitude 0 is the Prime Meridian
4. It runs through Greenwich, England
5. It has divided the Earth into eastern and western hemispheres since 1884
6. Longitudes run 180° E through 0° to 180° W (which is 180° E)
7. Roughly zigzagging through longitude 180 is the International Date Line
Crossing it moving west adds a day
Crossing it moving east subtracts a day
If Phileas Fogg had traveled west, he would have lost his wager
8. Hours are measured in 15° increments
Every 15° east, the time is one hour later; every 15° west, the time is one hour earlier
Our time zones try their very best to conform
Latitude Facts
1. I like latitudes
So much, in fact, that I wrote this whole post just to get here
2. Latitude 0 is the equator
It is 10,000 km away from the N or S Pole
3. Latitudes run 90° S through 0° to 90° N
That's penguins to Ecuadorian cacao beans to Santa; what's not to like?
4. Latitude 66.5° N, for now, is the Arctic Circle
It is 2,620 km S of the N Pole
From this line and everything northwards, the Sun never sets on the June solstice
Nor doth it rise on the Dec solstice
5. Latitude 66.5° S, for now, is the Antarctic Circle
It is 2,620 km N of the S Pole
From this line and everything southwards, the Sun never sets on the Dec solstice
Nor doth it rise on the June solstice
6. Latitude 23.5° N is the Tropic of Cancer
It is 7,400 km S of the N Pole
It is the northernmost latitude where the rays of the Sun strike at 90°
Further north, the rays of the Sun hit the Earth at an angle and are less intense
7. Latitude 23.5° S is the Tropic of Capricorn
It is 7,400 km N of the S Pole
It is the southernmost latitude where the rays of the Sun strike at 90°
Further south, the rays of the Sun hit the Earth at an angle and are less intense
8. The tropics is the band between the Tropic of Cancer and the Tropic of Capricorn
9. A sub-solar point is a point on a planet where the Sun appears to be directly overhead
A zero-shadow day is a day in which the Sun is at a sub-solar point at noon
(The Sun is never at a sub-solar point when it is not the middle of the day)
10. Zero-shadow days are dependent upon latitudes
Areas outside the tropics never have zero-shadow days
At the Tropic of Cancer, a zero-shadow day occurs on the June solstice
At the Tropic of Capricorn, a zero-shadow day occurs on the Dec solstice
At the equator, zero-shadow days occur on the two equinoxes
At other places in the tropics, two zero-shadow days occur some time
For the northern hemisphere, the first is about Apr-May and the second about is Jul-Aug
For the southern hemisphere, the first is about Oct-Nov and the second is about Jan-Feb
Earth at Summer Solstice, Study.com
Oil Painting by Joseph-Nicolas Robert-Fleury, 1847
