Introduction to Astronomy

Define the following terms: Universe – everything that exists, including all matter and energy everywhere Astronomy – the study of what is beyond Earth (planets, stars, galaxies, black holes, etc,)

Constellations – groups of stars that appear to form shapes or patterns (e.g. big dipper)

Solar system – the Sun and all the planets (and their moons) that revolve around it.

Galaxies A galaxy is a system of stars and interstellar matter. Galaxies may contain thousands of stars or trillions of stars. What is the name of our galaxy?

Non-luminous – not emitting light There are many non-luminous objects in space. Moons and planets do not give off light, but are visible because they REFLECT light

Luminous – give off light Stars and comets are examples of celestial objects that emit light. These objects are highly visible (especially at night). Our Sun (our closest star) emits light constantly, but we only see it when our side of the planet has rotated toward the Sun.

Star – a large collection of matter that emits huge amounts of energy (light, UV and infra-red radiation, X-rays, ). Planet – matter (gas or rocky material) that is generally spherical, and revolves around a star.

How is a star different from a planet? Stars Far beyond our solar system (very far from Earth) Usually larger than planets Emits its own light Surface is very hot Appears to twinkle Planets Within a solar system There are many (7) close to Earth Usually smaller than stars Nonluminous Have cold surfaces Produce steady light (when visible)

Astronomical Units The distances between the Sun and planets in our solar system are great – so large, in fact that it is difficult to comprehend. Astronomers have tried to simplify the concept by using astronomical units to measure and represent these distances.

Astronomical Units This is defined as the average distance between the Earth and the Sun. About 150 million kilometers. The equation used to calculate the astronomical unit for other planets is: Distance of planet from Sun Distance of Earth from the Sun

Astronomical Unit If the astronomical unit for a planet is less than one, the planet is closer to the Sun than the Earth. The astronomical unit for Earth = 1 a.u. If the astronomical unit for a planet is greater than one, the planet is further from the Sun than the Earth.

Light Year The distance a beam of light can travel through space in one year. 63 000 AU 9000 billion km Used for measuring distances beyond our solar system

List the 9 (really 8) planets from closest to the Sun to furthest. Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto

The Effects of Planetary Motion Define the following terms: Rotation – the spinning of an object around it’s axis. The Earth spins around an imaginary axis that appears to run from the North Pole, through the centre of the planet to the South Pole.

Earth’s Rotation

Earth’s Rotation It takes the Earth 24 hours (one day) to spin completely one time around it’s axis. This motion causes objects beyond the Earth (Sun, Moon, stars and other planets) to appear to move across our sky from EAST to WEST.

Earth’s Rotation

Earth’s Rotation Rotation causes us to experience 2 phenomena: Alternating day and night Gravity

Earth’s Revolution Like all planets in our solar system, the Earth revolves around the Sun.

Earth’s Revolution It takes the Earth approximately 365.25 days (a leap year adds the extra day every 4 years) to complete a single orbit around the Sun. This is known as an orbital period. We call this orbital period one year on our planet.

Earth’s Revolution The revolution of the Earth around the Sun causes us to experience different seasons. Since the Earth spins on it’s axis with a slight tilt, there are points when the Northern and Southern hemispheres of the planet are closer or further away from the Sun than at other times of the year.

Earth’s Revolution When the Northern hemisphere is tilted toward the Sun, we experience summer. At the same time, the Southern hemisphere is tilted away from the Sun. They would be experiencing winter.

Earth’s Revolution

Moon’s Revolution Moons (which are natural satellites) revolve around planets. Our moon revolves around Earth. Some planets (like Saturn) have more than one moon. Some planets have no moons. It was thought that Pluto may once have been a moon of Neptune, that instead began revolving around the Sun.

Moon’s Revolution

Explain where you would find the North Star (Polaris). Polaris (or the North Star) is a star that seems to be located directly above Earth’s North Pole. Because we rotate around this pole, we are always able to see Polaris (it is always directly above us).

Polaris (the North Star)

Why do you think that the North Star is important to navigation? Since the North Star is always above the North Pole, it is always an indicator of where North is (as a compass point). The North Star is part of the Little Dipper constellation which is always visible in the Northern Hemisphere.

Polaris in the Little Dipper

Pointer Stars Pointer stars are stars that can be used as points of reference in the sky to identify the locations of other constellations.

Star Map

Terrestrial vs. Gas Giant Planets The planets in our solar system can be divided into 2 categories, based on size, location and composition: Terrestrial or Inner Planets – these are the 4 small, rocky planets that are closest to the Sun. Mercury, Venus, Earth and Mars are terrestrial planets.

Terrestrial (Inner) Planets Mercury Venus Earth Mars

Terrestrial vs. Gas Giant Planets Gas Giant or Outer Planets – these are the 4 large planets found outside the asteroid belt of our solar system. The outer portions of these planets are made of gases (hydrogen, helium, methane), but it is believed that they have a small rocky core. Jupiter, Saturn, Uranus and Neptune are gas giants.

Gas Giant (Outer) Planets Jupiter Saturn Uranus Neptune

Properties of Mercury Mercury is the closest planet to the Sun sunlight it receives is about 10 times brighter than what we receive on Earth. It takes only 88 Earth days to revolve around the Sun. rotates slowly (about 59 Earth days for one rotation).

Properties of Mercury has no atmosphere (no layer of gases surrounding it’s surface). Because it lacks an atmosphere, the surface temperature of the planet is variable. On the side that faces the Sun the temperature can reach 426 °C. The side that faces away from the Sun drops to about - 180 °C.

Properties of Mercury The lack of atmosphere means that there is no protective layer that could potentially burn up meteors that hit the planet. Because of this, the surface of the planet is heavily cratered.

Properties of Mercury

Properties of Venus Earth’s sister planet – it is similar in size, density and chemical composition. the hottest planet, with surface temperatures reaching 470oC. surface of Venus is largely volcanic.

Properties of Venus The atmosphere of Venus is primarily made up of Carbon Dioxide (a greenhouse gas) that traps the heat from the Sun. This is why the surface temperature of the planet is so high.

Properties of Venus A day on Venus is longer than a year. It takes Venus 224 Earth days to revolve around the Sun. It takes 243 Earth days for Venus to completely spin once on its axis. This planet spins in the opposite direction to all other planets.

Properties of Venus The planet is named for the Roman god of love and femininity.

Properties of Venus

Properties of Earth the only planet that we know with life. has an abundance of liquid water it’s atmosphere contains a large quantity of oxygen (about 20%). temperatures on Earth are moderate, ranging from -85oC to 58oC at the extremes.

Properties of Earth

Properties of Mars known as the Red Planet. The soil on the surface of the planet is orangish red, due to the high iron content. Mars is thought to have had glaciers and running water on it’s surface. It now appears dry and barren. This has led scientists to think that there may have been some life on the planet, though none has been found.

Properties of Mars A day on Mars is similar in length to Earth (24.7 hours), but because of it’s distance from the Sun, it takes twice as long to orbit (about 687 Earth days). Surface temperature ranges from -120oC to 30oC.

Properties of Mars

Properties of Jupiter the largest planet in our solar system (diameter is 11 times greater than Earth). day on Jupiter lasts approximately 10 Earth hours. It takes nearly 12 years to orbit the Sun. Surface temperature on the planet is about -160oC (very far from the Sun).

Properties of Jupiter The planet has a huge hurricane (larger than 2 Earths), the Great Red Spot.

Properties of Jupiter

Properties of Saturn Saturn is the second largest planet in the solar system. Surface temperature on the planet is -180oC. the least dense planet (would float in water)

Properties of Saturn The rings of Saturn are made almost entirely of ice, with some contamination from dust and other chemicals.

Properties of Saturn

Properties of Uranus Uranus takes about 84 years to revolve around the Sun, and 17 hours to rotate once. Due to it’s distance from the Sun, the surface temperature of Uranus is -210oC. Uranus also has rings, similar to Saturn’s rings, but much less extensive Rotates on it’s side

Properties of Uranus

Properties of Neptune Neptune is known as the Blue Planet. It’s surface temperature is -210oC. It takes 15.6 hours to rotate, but 165 years to revolve around the Sun. Neptune has a hurricane known as the Great Dark Spot.

Properties of Neptune

Properties of Pluto Pluto is no longer considered to be a planet. It does not have the same characteristics as it’s closest planets (the gas giants) and is thought to have once been a moon of Neptune that fell out of orbit around Neptune and was caught in orbit around the Sun.

Properties of Pluto Pluto does share characteristics with a group of celestial objects known as dwarf planets (objects that orbit the Sun, are rounded by their own gravity, but which have not cleared their orbits – meaning it has not become gravitationally dominant, and there are other bodies of comparable size other than its own moons not under its gravitational influence.

Properties of Pluto