Solar System Notes PDF

# Touring the Night Sky ## Astronomy The branch of science that studies objects beyond Earth, in what we sometimes refer to as "outer space". Any object in space is considered to be a celestial object. Everything that physically exists is part of what we call the Universe. ## Star A star is...

# Touring the Night Sky ## Astronomy The branch of science that studies objects beyond Earth, in what we sometimes refer to as "outer space". Any object in space is considered to be a celestial object. Everything that physically exists is part of what we call the Universe. ## Star A star is a massive celestial body composed of hot gases that radiates large amounts of energy. We are able to see may stars in the night sky because they are luminous, which means that they produce and emit their own light. ## The Sun The closest star to our Earth is the Sun. It is of average size compared to other stars. It is only 150,000,000 km away from our Earth which is very close compared to other stars. The next closest is 300,000 times farther away. Life would not be possible on Earth without the energy produced by the Sun. ## Planets A planet is a large celestial object that travels around a star. There are 8 planets in our Solar System. The first four are terrestrial (made of rock): - Mercury - Venus - Earth - Mars The last four are gas giants (made of gases and some liquids): - Jupiter - Saturn - Uranus - Neptune ## Moon A moon is a type of satellite, a celestial object that travels around a planet in a closed path (orbit). Not all of our planets have moons. Mercury and Venus don't but Jupiter and Saturn each have 68 or more moons. Earth has one natural satellite called the Moon. It is non-luminous and thus we are only able to see it when the Sun’s light is reflecting off of it. ## Galaxies Galaxies are huge, rotating collections of gas, dust and billions of stars, planets, and other celestial objects. Astronomers looking through telescopes are discovering that there are billions of galaxies scattered throughout the Universe! ## The Milky Way This is the name of our galaxy. It contains more than 300 billion stars, including the Sun. It appears as a hazy band of white light in the night sky. ## The Sun The Sun emits waves of energy of many wavelengths (called the electromagnetic Spectrum) at the speed of light. This Spectrum consists of: - Radio waves - Microwaves - Infrared rays - Visible light - Ultraviolet light - X-rays - Gamma rays The Sun is composed by many layers of gas. The core is the highest temperature (about 15,000,000 degrees Celsius) and this is where nuclear fusion takes place. Hydrogen atoms are brought together to make helium atoms and this releases tremendous amounts of energy. **Sunspots:** Dark spots appearing on the Sun's surface that are cooler than the area surrounding them. **Solar Flares:** Gases and charged particles expelled above an active sunspot. **Solar prominence:** Low-energy gas eruptions from the Sun's surface that expand thousands of kilometers into space. ## The Auroras Solar wind (high energy particles ejected by the Sun) reaches the Earth and follows the Earth's magnetic fields at the North and South pole. These particles interact with the elements in the Earth's atmosphere and causes them to produce different colours. This brilliant display in our North is called the Northern Lights, or Aurora Borealis. # The Solar System The Solar System consists of the Sun, the eight planets and their moons, and billions of other smaller celestial objects. All of these celestial objects orbit the Sun. Distances are so great that astronomers must use a unit of measure other than the kilometer (it’s too small). The astronomical unit, or AU, is the average distance between the Sun and Earth – approximately 150,000,000 km. For example, Jupiter is 5.2 AU away from the Sun. ## Planets ### Mercury - Very hot - No atmosphere ### Venus - Bright in the night sky - Very hot (greenhouse effect) ### Earth - The "blue" planet ### Mars - The "red" planet - Rusty soil ### Jupiter - Largest planet - Gas giant - Giant red spot (a big storm) on the surface ### Saturn - Second largest planet - Gas giant - Recognizable rings ### Uranus - Made of gas ### Neptune - Made of gas ## Asteroid Belt Asteroids are small celestial objects in the Solar System composed of rock and metal. They orbit around the Sun but are too small to be considered planets. The asteroid belt is found between the orbits of Mars and Jupiter. The largest ones can be as large as 950 km across (and most are irregularly shaped). ## Meteoroids These are pieces of metal or rock in the Solar System that is smaller than an asteroid. Meteoroids can get pulled into Earth's atmosphere and burn up in the sky as it falls (these are now called meteors). When it hits the ground it is now called a meteorite. Meteor showers occur when many meteors are burning up in the Earth's atmosphere. ## Comets These are large chunks of ice, dust and rock that orbit the Sun. Some take years to orbit the Sun, some take thousands of years. As it moves through space and closer to the Sun, the ice starts to heat up and leaves gaseous water which shows up as a streak behind it. # Motions of the Earth, Moon and Planets ## Earth’s Rotation The Sun is known to rise in the East and set in the West. The reason for this is the Earth's rotation. The Earth rotates once every 24h and the side facing away from the Sun experiences night. The side facing the Sun is daytime. ## Earth’s Revolution The Earth also revolves around the Sun which takes about 365.25 days. The Earth travels in an ellipse, not a perfectly round orbit. This means that at certain times of year we are closer to the Sun than others. The average distance from the Sun is an orbital radius. The Earth’s revolution affects our view of the celestial objects in the sky. ## Motions of the Moon The Moon also rotates on its axis, at the same time as it revolves around the Earth. The Moon rotates once as it revolves once around the Earth so we never see the other side of the Moon because of this. ## Earth’s Tilt Earth's rotational axis is tilted 23.5 degrees from the vertical compared to the plane of Earth's orbit around the Sun. The tilt affects the average daytime temperature experienced by Earth's hemispheres. The Earth's four seasons aren't caused by the Earth's distance to the Sun (in fact, in winter we are closest to the Sun!). The seasons are caused by the tilt. When the northern hemisphere is tilted toward the Sun, it is summer time there, and at the same time the southern hemisphere is tilted away (which is their winter). When Earth's axis is most inclined toward or away from the Sun, we call it a solstice (there are two per year). The summer solstice is around June 21. The winter solstice is around December 21. Between the solstices are the equinoxes (around March 21 is the vernal equinox - beginning of spring and around September 21 is the autumnal equinox occurring around September 21 marking the beginning of autumn). ## Eclipses They are spectacular astronomical events that occur when the position of one celestial object blocks, or darkens: - the view of another celestial object - from Earth **Solar eclipses:** happen when the Moon blocks the Sun so it gets dark on a specific spot on the Earth. Solar eclipses were often associated with bad omens or events about to happen. **Lunar eclipses:** Happen when the Earth blocks the Sun's light that normally shines on the Moon. It appears like the moon is disappearing. Lunar eclipses were believed by some to be caused by some kind of creature swallowing the Moon. ## Tides – The Pull of the Moon Tides are the rising and falling of the surface of the oceans, and are caused by the gravitational pull of the Moon. The water on Earth slightly gets attracted to the Moon and water on that side tends to get deeper (high tide). The force of gravity keeps the Moon in orbit around the Earth. This gravitational force also keeps the Earth revolving around the Sun. Any objects with mass have gravitational forces. # History of Thought About 2000 years ago, the Greek astronomer Claudius Ptolemy believed that the Sun and the planets revolved around Earth. This idea was widely accepted until the Middle Ages. Nicholas Copernicus (1473 - 1543) proposed a model placing the Sun at the center of the Solar System, called the heliocentric model. In the early 1600’s Galileo used the telescope to discover that planets had other celestial objects orbiting around them and many astronomers at the time didn’t believe his discoveries. Galileo’s discoveries eventually convinced everyone that the heliocentric model was correct. # Interactions of Earth and Sun - If Earth's orbit brought us much closer to the Sun, our planet might be a lifeless, scorched desert. - If Earth’s orbit were much farther away, our planet might be a frigid, icy wasteland. - Astronomers call Earth’s position in the solar system the “Goldilocks zone”. However, we need to be protected from the Sun's energy. Fortunately, the Earth has a magnetosphere and atmosphere to protect us. ## Magnetosphere We have an invisible field of magnetic force that surrounds the planet. This is called the magnetosphere. It deflects the solar wind (high energy particles made by the Sun) and prevents much of it from entering the atmosphere. This energy does enter, but at the poles creating an aurora. In the North it is the Aurora Borealis (or "Northern Lights"). ## Atmosphere The Sun is a good thing but too much is not. The Sun emits forms of energy that are harmful to living things. These include: - UV (ultraviolet) - X rays Ozone and other gases in our atmosphere interact with this incoming energy and shields us from it. The atmosphere also helps to trap heat that would otherwise escape back into space. This helps keep the Earth at the right temperature for life to thrive. It protects us from temperature fluctuations (night/day) and makes life as we know it possible. Earth has many environmental conditions ideal for maintaining life. Scientists have been discovering distant planets ("exoplanets") for years, that all orbit around distant stars. As of the year 2020, over 4000 exoplanets have been discovered. Astronomers estimate that out of the 300 billion (or so) stars in our galaxy alone, there might be billions of Earth-like planets out there orbiting those stars. To date, only a handful of Earth-like planets have been discovered (so far). # Patterns in the Night Sky Many civilizations, both in the past in present, believe that celestial objects are connected to events that occur on Earth. Stars were also used for navigation, especially when sailing across oceans. One easily recognized star is called Polaris, or the North Star. If you continue the line of the Earth's axis, it extends all the way pointing at the North Star. It can be found lining up certain stars in the constellation called the Big Dipper. ## Constellations Some stars in the night sky appear to form patterns called constellations (88 of them). People started naming these patterns after their heroes, mythical monsters and animals. A star map shows the relative positions of the stars in a particular part of the sky. It can be used to: - Recognize celestial objects in the sky. - Observe the motions of these objects **Note:** The stars may appear on the same plane in the sky but in reality these stars may be much more distant than other stars, but just appear to be beside each other. Some popular constellations: - Big Dipper (discuss how to find the North Star) - Orion ## Different Views of the Sky Not everyone thought the same way about the sky, even thousands of years ago. **The Canadian First Nations:** **1. Kwakiutl** - Believed a lunar eclipse occurred when the sky monster tried to swallow the Moon. **2. Tsimshian** - Believed that each night the Sun went to sleep in his house but allowed the light from his face to shine out of the smoke hole in the roof. The stars were the sparks that flew out of the Sun's mouth. The full Moon was the Sun's brother who rose in the East when the Sun fell asleep. **Other ideas:** - About 7000 years ago, cycles of the Sun and Moon were observed to make calendars and used to tell people when to plant and harvest crops. - 3000 years ago the Chinese made a 365 day calendar from these cycles. - Both the Chinese and the Greeks created star maps more than 2000 years ago. - The Maya in Central America build temples to keep track of planets. - In Egypt, structures were built where the Sun shines inside only two special days of the year. - Stonehenge (in England) also can be used to indicate the longest day of the year and to predict eclipses. # Satellites A satellite is a celestial object that travels around a planet. The Earth has one natural satellite orbiting it - the Moon. Earth also has thousands of other satellites circling it at different altitudes and orbits, but these are all made by humans. Artificial satellites such as these help us to: - Forecast weather - Monitor agriculture - Aid in telecommunication or navigation - Assist military activities (security satellites) - Explore the Universe Human-occupied spacecraft, such as the Space Shuttle and space facilities such as the International Space Station, also function as artificial satellites. The first artificial satellite was launched in 1957 by the Soviet Union. Canada has been a world leader in developing satellite technology over the last 50 years. We have become renowned for building some of the most powerful telecommunications and Earth observation satellites. ## Staying in Orbit How do these satellites keep orbiting Earth without plunging back to the ground? The force of Earth's gravity continuously pulls the satellite toward Earth. However, the forward motion of the satellite and the curvature of Earth prevent the satellite from getting any closer to the surface. When engineers launch a satellite into Earth's orbit, they launch it much like a powerful cannon. It needs to attain sufficient velocity to make sure that when Earth's gravity pulls it down, it continuously falls around the Earth's curvature. ## Types of Orbits Satellites around Earth are around 200 km to more than 35,000 km above the Earth. The higher the altitude, the longer the orbital period – the time it takes to circle Earth. ### Low Earth Orbit Satellites - Are found at altitudes up to 2000 km. - Most human-occupied spacecrafts and those conducting Earth observations are found here. ### Medium Earth Orbit Satellites - Are found at altitudes up to 35,000 km. - Two dozen of these satellites are part of the global positioning system (GPS). - They travel about 11,000 high and can pinpoint the location of things on the Earth as long as there are at least three satellites visible at any given time. ### Geostationary Orbit Satellites - Have orbital paths directly over Earth's equator with a period equal to the period of Earth's rotation. - They appear not to move and are used for weather and communication (broadcast TV, radio, etc).