The Sun

• The Sun, a hot ball of hydrogen and helium.
• Source of all the energy and magic in the solar system. The miniscule amount we get from the other stars.
• The amount of magic we receive from a celestial body depends on the amount of light it sends us, as well as its size, and the Sun’s average diameter is 1,391,980 kilometres, about ten times as great as the largest planet!
• About 400 thousand times as much as the full Moon and 12.5 billion times more than the next brightest star, Sirius.
• Its surface temperature is about 10,000 degrees Fahrenheit.
• Sol, the Latin word for sun – which is where the word “solar” comes from.

The sizes of the planets

• Planet reflects a significant amount of magic to us.
• Jupiter, the largest planet, is more than 28 times as big in diameter as Mercury, the smallest one.
• The diameter of Saturn given here doesn’t include its rings, whose diameter is about 280,000 kilometers.
• The planets are divided into two groups: the inner planets and the outer planets.

The Inner planets

• The inner planets are Mercury, Venus, Earth, and Mars.
• Separated from the outer ones by the asteroid belt.
• Have rocky surfaces and are much smaller than the outer ones.
• They reflect just as much magic to us because they are closer to both the Sun and Earth.
• Venus reflects more magic to us than any of the outer planets.
• Mars and Mercury reflect more than two of them.

Mercury
• The innermost planet
• No moons
• With mountains, plains and crates.
• Very thin atmosphere
• 200 trillion times less pressure than Earth’s atmosphere.
• Mostly of oxygen, sodium and helium.
• Does not affect the magic reflected from the surface.
• Temperature as high as 427°C
• Temperature as low as -220°C

Venus
• No moons
• Thick layer of clouds made mostly of sulphuric acid.
• Mountains, plains and depressions.
• Atmosphere exerts 92 times as much pressure as the Earth’s.
• Made up of mostly carbon dioxide with a bit of nitrogen.
• Temperature reaching about 462°C, night and day.
• Tallest mountain – Maxwell Montes, where the temperature is 380°C
• Because Venus is almost the same size as the Earth, they are often called sister planets.
• Rotate in clockwise/Retrograde direction

Earth
• Our home planet
• One moon, called Luna or Selena. Tidally locked.
• The moon is locked to earth meaning that tidal forces exerted by earth make same side of the moon face us at all times.

Mars
• Mountains, plains and craters.
• Reddish because of iron oxide
• Made up of different types of rocks.
• Is no liquid water on the surface.
• Water was discovered underneath the surface. Speculation that life may once have existed there and possibly still does.
• The poles are also covered with frozen water and, in the winter, frozen carbon dioxide as well.
• Its atmosphere, which is made up of mostly carbon dioxide, exerts about 100 times less pressure than the Earth’s.
• Creates dust storms all around the planet
• Temperature ranges from -143°C at the poles to as high as 35°C at the equator at Martian noon when the sun is highest in the sky.
• Two moons, Phobos and Deimos. Tidally locked.

The Outer Planets

• The outer planets: Jupiter, Saturn, Uranus, and Neptune.
• They are all made out of gas.
• They don’t have a surface, but they have either a solid or liquid core.
• “The Gas Giants”
• All of the outer planets have rings, although only Saturn’s are bright enough to be seen through a small telescope.

Jupiter
• Clouds of ammonia crystals alternating between darker and lighter colours.
• Great Red Spot. It’s the largest of many vortexes, caused by interaction between the varying circulation patterns of the gases carrying the clouds of different colours.
• Mostly hydrogen with small amount of helium and some trace gases.
• Temperature outside of the planet is about -160°C.
• Hotter than the surface of the Sun near the core.
• Emits a lot of radiation.
• Incredibly dangerous to get near it.
• 79 known moons.
• Four largest moons, lo, Europa, Ganymede, and Callisto. Called the Galilean moons. Discovered by Galileo.

Saturn
• Made up of mostly hydrogen and helium.
• A vortex at each of its poles.
• Its prominent rings. These are not solid but made up of chucks of frozen water ranging from about ten meters to the size of a speck of dust.
• Rings are only about 20 meters thick.
• They extend from 6,630 to 120,700 kilometres outwards from the planet’s equator.
• Galileo was the first one to see the rings.
• Telescope wasn’t powerful enough for him to see that they were actually separated from the body of the planet. Called them ears.
• Temperature is about -185°C.
• 82 known moons
• Largest of which is Titan
• Atmosphere almost 1.5 times as much pressure as the Earth’s.
• Only 62 of those moons had been known, October 7, 2019. The international Astronomical Union announced that 20 more of Saturn’s moons have been discovered by a team led by Scott Sheppard using the Subaru telescope on Hawaii’s Mauna Kea.

Uranus and Neptune
• Cannot be seen with the naked eye.
• Neptune does have a dark spot.
• It’s even colder out by Uranus
• Uranus has 27 known moons.
• Neptune has 14 moons. Its largest, Triton.
• Both planets are primarily made up of hydrogen and helium
• Also have a fair amount of ice, namely water, ammonia, and methane ice.
• Sometimes called the “ice giants”.
• Uranus rotates clockwise/retrograde direction

The motion of the planets

• It appears as if the Moon, the Sun, the planets, and the stars all revolve around Earth once per day.
• Ancient Greece, this observation led to the geocentric model of the solar system. Created by Ptolemy, a Greek mathematician, astronomer, and geographer.
• The Moon is the closest body to the Earth, followed by Mercury, Venus, the Sun, Mars, Jupiter, Saturn, and finally the fixed stars.
• Ptolemy studied the movements of the bodies in the sky and noted that the planets moved with respect to the stars. To account for this motion, he assumed that the planets revolved in perfect circles, called epicycles, around a point that, in turn, revolved around Earth in a circle.
• Aristarchus of Samos, believed that the Sun, not Earth, was the centre of the solar system.
• Model is termed “heliocentric,” after the Greek word ‘helios,’ meaning sun.
• The Polish astronomer Nicolaus Copernicus wrote a book expounding the same model, which was published in 1543, some 18 centuries after Aristarchus did. The heliocentric model wasn’t accepted right away, although it received support from Galileo, who became convinced of its correctness when he observed the phases of Venus, partly because both the Protestant and Catholic Church condemned heliocentrism as being impious and forced him to recant under threat of torture.
• The fact that Venus exhibits the full range of phases proves that Ptolemy’s geocentric model was incorrect, because if Venus were always closer than the Sun to Earth than the Sun, it would only ever be in the crescent phase.
• There is a geocentric model, proposed by the pagan Martianus Capella in the fifth century C.E., that is compatible: the Sun, Mars, Jupiter, Saturn, and the stars all revolve around the Earth, but Mercury and Venus revolve around the Sun. Fortunately, Galileo chose to align this observation with the Copernican model, which was later proven to be essentially correct.
• Like Ptolemy, Copernicus believed that the planets could only move in circles, so he too introduced epicycles.
• Tycho Brahe made some extremely accurate observations of the positions of the planets in the sky. Which Copernicus’s model couldn’t account for.
• Johannes Kepler studied Brahe’s published observations and proposed an alternative heliocentric model taking them into account. This model was governed by a series of three laws.
Kepler’ laws

• Kepler’s First Law states that a planet revolves around the Sun not in a circle but in an ellipse. The Sun isn’t in the middle of the ellipse but off to one side. First Law says exactly where in the ellipse the Sun is: it’s at one of two points in the interior of the ellipse called foci.
• Kepler’s Second Law states that an imaginary line between the Sun and any planet sweeps out equal areas in equal amounts of time. A planet will speed up as it approaches the Sun and slow down as it recedes.
• Kepler’s Third Law says that if you divide the square of the time it takes for any planet to revolve around the Sun by the cube of the average distance from the planet to the Sun, you get the same answer no matter which planet you choose. This means that planets that are closer to the Sun move faster than planets that are farther away
• By examining them, you’ll see that Mars and Mercury don’t travel in circles and that the Sun isn’t in the centre of the paths they take, illustrating Kepler’s First Law. The Second Law is seen from the fact that 44 days is half the time it takes Mercury to revolve around the Sun, and yet the planet has moved just under half way around its orbit, as it is farther away from the Sun during this half. You’ll also note that while Mercury moves almost a full half-revolution around the Sun in this time period, Venus only moves about a quarter, and Mars even less, illustrating the Third Law.
• Kepler’s Laws describe how the planets move.

Newton law’s

• The English mathematician, physicist, and astronomer Isaac Newton discovered three laws of motion.
• 1. An object remains at rest or continues to move in a straight line at a constant speed unless acted upon by an outside force.
• 2. The force required to make an object change its speed and/or direction of motion is equal to the mass of the object multiplied by the rate of change.
• 3. If one object exerts a force on a second object, then the second object will exert the same amount of force on the first one, but in the opposite direction.
• Newton reasoned that an unsupported object falls to the ground instead of floating in the air because a force acts on it.
• If you could throw it hard enough, your stone would never hit the ground, but would continue to fall around the curvature of our spherical planet.
• This same force that causes our stone to fall keeps the Moon from travelling in a straight line away from the Earth.
• The Moon is moving fast enough that instead of hitting the Earth, it falls continuously around it - its revolution.
• Newton concluded that the force that both pulls an unsupported object near the Earth to the ground and holds the Moon in its revolution is exerted by the Earth itself, and he called that force gravity.
• It is this force that makes a planet speed up as it approaches the Sun and slow down as it recedes. He concluded that everybody attracts every other body, and he called that principle the Law of Universal Gravitation.
• The more mass a body has, the more force it will exert on others. However, Galileo had previously shown that a heavy object falls at the same rate as a light one, meaning that the more massive a falling object, the more force the Earth must exert on it to make it fall at the same rate, according to Newton’s Second Law. From Kepler’s laws of motion, Newton also concluded that the farther apart two objects are, the smaller the force will be by an amount equal to the square of the distance between them, and that’s why planets that are closer to the Sun move faster than planets that are farther away. By Newton’s Third Law of Motion, the falling object will exert the same amount of force on the Earth but in the opposite direction. The same holds true for any two bodies, including celestial ones. In fact, the planets, especially Jupiter, do make the Sun wobble a bit.

The rotation of the planets

• Aside from revolving around the Sun, each planet also rotates about an imaginary line called an axis. That’s why the Sun, the planets, and the stars all appear to revolve around Earth.
• There is an imaginary circle around the middle of the planet, equally distant from the poles, called the equator.
• The plane of the equator is usually tilted relative to the plane of the planet’s orbit. The angle between these planes is called the inclination.
• Period of revolution, perihelion, aphelion, inclination, and period of rotation of each of the eight planets in addition to the corresponding values for the Moon.
• Distance between the Sun and a planet is too big to be expressed in kilometres.
• Another unit is used, called the Astronomical Unit (A.U.), which is the average distance between the Sun and the Earth: 149,597,870.7 kilometers (92,955,807.3 miles).
• The rotation periods of Venus and Uranus are negative. Their equators are actually inclined more than 90 degrees from their orbits.
• The period of rotation of the Earth isn’t exactly one day. Earth makes one full rotation, it also moves a bit around the Sun; consequently, it has to rotate a little more before the Sun gets to the same place in the sky and a full day has passed!