First Year Astronomy Notes
written by Elizabeth Wonders
There you go, your brand-new notes for Astronomy 101! Good luck! <3 (Notes on other subjects are coming out. Owl me if you would like to request a specific subject published sooner.)
Last Updated
05/15/24
Chapters
10
Reads
750
Lesson 7) The Sun and the Planets in the Solar System
Chapter 7
- The Sun is a hot ball of hydrogen and helium that is the source of energy and magic in the solar system
- The Sun has a diameter of 1,391,980 kilometers, about ten times larger than the largest planet
- The Sun emits about 400 thousand times more light than the full Moon and 12.5 billion times more light than Sirius, the next brightest star
- The surface temperature of the Sun is about 10,000 degrees Fahrenheit
- The inner planets, Mercury, Venus, Earth, and Mars, have rocky surfaces and reflect a significant amount of magic
- Venus reflects more magic than any of the outer planets, and Mars and Mercury reflect more magic than two of them
- Mercury has no moons and a thin atmosphere, with extreme temperatures ranging from 427°C to -220°C
- Venus has no moons and a thick layer of sulphuric acid clouds, with temperatures reaching about 462°C
- Earth has one moon called Luna or Selena, which is tidally locked to Earth
- Mars has two moons, Phobos and Deimos, and a reddish surface covered in iron oxide and dust, with temperatures ranging from -143°C to 35°C
- The outer planets, Jupiter, Saturn, Uranus, and Neptune, are made of gas and have either a solid or liquid core
- All outer planets have rings, with Saturn having the most prominent and visible rings
- Jupiter has clouds of ammonia crystals and the largest vortex called the Great Red Spot, with a temperature hotter than the surface of the Sun near the core
- Saturn's rings are made up of chunks of frozen water and extend from 6,630 to 120,700 kilometers outwards from the planet's equator
- Saturn has 82 known moons, including Titan with a dense atmosphere and higher pressure than Earth's
- Uranus and Neptune cannot be seen with the naked eye
- They require binoculars or a telescope to be observed
- They don't show much surface features, except for a dark spot on Neptune
- Uranus has 27 known moons, while Neptune has 14, with Triton being the largest
- Both planets are primarily made up of hydrogen and helium, but also contain ice
- They are sometimes referred to as the "ice giants"
- Ancient Greeks had different models of the solar system: geocentric (Earth-centered) and heliocentric (Sun-centered)
- Ptolemy's geocentric model involved planets moving in perfect circles called epicycles
- Aristarchus of Samos proposed the heliocentric model, but it was not accepted at the time
- Copernicus improved the heliocentric model but introduced epicycles as well
- Kepler's laws of planetary motion: 1) planets move in ellipses with the Sun at one focus, 2) an imaginary line between the Sun and a planet sweeps out equal areas in equal time, 3) the square of a planet's orbital period divided by the cube of its average distance from the Sun is constant for all planets
- Kepler's laws explain the motion of planets and can be observed in the paths of Mercury, Venus, and Mars
- Length of a planet's orbit is the sum of aphelion and perihelion
- Eccentricity of a planet's orbit is calculated as (aphelion - perihelion)/length
- Isaac Newton discovered the three laws of motion:
- An object remains at rest or moves in a straight line at a constant speed unless acted upon by an outside force
- The force required to change the speed or direction of an object is equal to the mass of the object multiplied by the rate of change
- For every action, there is an equal and opposite reaction
- Newton concluded that the force that pulls objects towards Earth and keeps the Moon in orbit is gravity
- The force of gravity between two objects depends on their masses and the square of the distance between them
- Each planet also rotates on an axis, which is inclined relative to its orbit
- The inclination of the equator relative to the orbit plane determines the rotation direction of a planet
- The table shows the period of revolution, perihelion, aphelion, inclination, and rotation period of each planet and the Moon
- Venus and Uranus have negative rotation periods because their equators are inclined more than 90 degrees, causing them to rotate backwards
- Earth's rotation period is not exactly one day due to its movement around the Sun, requiring a little more rotation for a full day to pass
