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note (2) Revolution – The time it takes for an object to orbit another object; Earth’s revolution around the Sun is 365.24 days. Rotation – The turning of an object around an imaginary axis running through it. Constellation – A group of stars that seem to form a distinctive pattern in the sky. Apparent Magnitude – The brightness of a star as seen from Earth. ● Smaller groups of stars that form patterns within a constellation are called asterisms, from the Greek word aster, meaning star. Latitude – The location above or below the equator. ● Constellations are groupings of stars that form distinctive patterns. The stars in these groupings appear to be close to each other, but they are not. ● A star’s apparent magnitude is its brightness as seen from Earth. ● Earth’s rotational axis points to Polaris, the North Star. For thousands of years, travellers have used Polaris and the constellations to navigate. ● Different cultures have different interpretations of the night sky. Tides – The rising and falling of ocean waters as a result of the Moon’s gravity and Earth’s gravity. Ellipse – A curve that is generally referred to as an oval or the shape of an egg. Phases of the Moon – The monthly progression of changes in the appearance of the Moon, which result from different portions of the Moon’s sunlit side being visible from Earth. ● Full- Fully illuminated ● Gibbous- Between fully-lit and half-lit ● Quarter- Half-lit ● Crescent- Between half-lit and not-lit ● New- No illumination Eclipse – The phenomenon in which one celestial object moves directly in front of another celestial object. Lunar Eclipse – The phenomenon in which the full Moon passes into Earth’s shadow. Solar Eclipse – The phenomenon in which the shadow of the Moon falls on Earth’s surface. Gravitational Force – The force of attraction between all masses in the universe. ● The tilt of Earth’s axis, combined with Earth’s motion around the Sun, gives rise to the seasons. ● ● ● ● We see different phases of the Moon, depending on where the Moon is in relation to Earth. During a lunar eclipse, the Moon passes through Earth’s shadow. During a solar eclipse, the Moon passes in front of the Sun. The tides are a result of the difference between the force of gravity on the side of Earth nearest the Moon and the force of gravity on the side of Earth farthest from the Moon. Planet – An object that orbits one or more stars (and is not a star itself), is spherical, and does not share its orbit with another object. Solar System – A group of planets that circle one or more stars. ● The planets Mercury, Venus, Earth, and Mars are called the inner/ terrestrial (Earth-like) planets. ● Jupiter, Saturn, Uranus, and Neptune are outer planets or gas giants. Comet – An object composed of rocky material, ice, and gas Asteroid – A small object that ranges in size from a tiny speck, like a grain of sand, to 500 km wide; most asteroids originate in the asteroid belt between Mars and Jupiter. Meteoroid – A piece of rock moving through space. Meteor – A meteoroid that hits Earth’s atmosphere and burns up. Meteorite – A meteoroid that is large enough to pass through Earth’s atmosphere and reach the ground, without being totally burned up. ● In addition to planets, the solar system contains many different objects, such as dwarf planets, asteroids, comets, and meteors. Refracting Telescope – A telescope that uses a lens to collect the light from an object. Reflecting Telescope – A telescope that uses a mirror to collect light from an object. Satellite – A human-made object or vehicle that orbits Earth, the Moon, or other celestial bodies; also, a celestial body that orbits another of larger size Hertzsprung–Russell – Diagram a graph that compares the properties of stars. Mercury ● ● ● ● Rocky ball covered in craters Slightly larger than our Moon Closest to the sun, with no atmosphere Extreme differences between day and night Venus ● ● ● ● ● “Earth’s sister planet”, similar size and composition to Earth’s Continuously covered in thick clouds Acid rain precipitates there Atmosphere of CO2 and N2 Large flat areas, volcanoes, and cracks (rifts) Earth ● ● ● 3rd from the Sun Water covers ¾ of Earth’s surface, only place with water in 3 phases (Liquid, solid, gas) Atmosphere of mainly N2, O2, and H20 vapour Mars ● ● ● ● The “red planet”, the iron on its surface gives it a rusty colour Has a volcano 3x higher than Mount Everest, it’s 265.5km high High winds of 900km/h (The strongest hurricane on Earth is 25km/h) Dust storms, and 2 polar ice caps Jupiter ● ● ● ● Largest planet, mass is 2 ½ times greater than the total mass of all the other planets combined Red Spot- The size of 3 Earths is a storm Made up of the gasses H2 and He 1 rotation = 10 hours Saturn ● ● Elaborate system of rings made of ice particles Planet is composed of H2 and some He gas Uranus ● ● ● Composition similar to Jupiter and Saturn, with a ring system of ice and dust Blue-green colour is from the methane gas (CH4) in its atmosphere It’s flipped on its side and appears to be rolling through its orbit Neptune ● ● Outermost planet Composition and atmosphere is similar to Uranus but is darker blue Orbital Radius – The average distance between the Sun and an object that is orbiting the Sun. ● Two models of the solar system are the geocentric model and the heliocentric model. ● The planets share many similar characteristics, but they also have many differences. ● The inner, or terrestrial, planets are rocky and small. The outer planets, or gas giants, are made of gases and are huge. ● The astronomical unit is defined as the average distance between Earth and the Sun. Solar Nebula – Theory the theory that describes how stars and planets form from contracting, spinning disks of gas and dust. Star – A celestial body made of hot gases, mainly hydrogen and some helium. Nebula – A vast cloud of gas and dust, which may be the birthplace of stars and planets. Protostar – Hot, condensed object at the centre of a nebula. Nuclear Fusion – The process of energy production in which hydrogen nuclei combine to form helium nuclei. Photosphere – The surface layer of the Sun. Sunspot – An area of strong magnetic fields on the photosphere. Solar Wind – A stream of fast moving charged particles ejected by the Sun into the solar system. Solar Nebula Theory – ● The solar nebula theory says that the Sun and the solar system formed from a spinning, contracting disk of gas and dust particles. ● Evidence supporting the solar nebula theory consists of heavily cratered objects, most planets rotating in about the same direction, most planets revolving in the same direction and in the same plane, and the existence of other planets around other stars. ● The Sun’s energy source is hydrogen. It converts matter into energy through nuclear fusion. ● Sunspots can produce solar flares, which send gigantic beams of charged particles into space. Absolute Magnitude – The magnitude of a star that we would observe if the star were placed 32.6 light-years from Earth. Spectral Lines – Certain specific wavelengths within a spectrum characterized by lines; spectral lines identify specific chemical elements. Main Sequence – A narrow band of stars on the H-R diagram that runs diagonally from the upper left (bright, hot stars) to the lower right (dim, cool stars); about 90 percent of stars, including the Sun, are in the main sequence. White Dwarf – A small, dim, hot star. Supernova – A massive explosion in which the entire outer portion of a star is blown off. Neutron Star – A star so dense that only neutrons can exist in the core. Milky Way – The galaxy that includes the solar system; appears as a hazy white band in the night sky. Galaxy – A huge collection of stars, planets, gas, and dust that is held together by gravity. Shapes of Galaxies Spiral Galaxy ● Looks like a pinwheel when viewed from above. ● Looks like a plate with a bulge in the middle when viewed from the side. Elliptical Galaxy ● Range in shape from a perfect sphere to an ellipse. ● Contain some of the oldest stars in the universe. Irregular Galaxy ● Do not have a regular shape. ● Made of newly forming stars and old stars. Star Cluster – A collection of stars held together by gravity. Open Cluster – A collection of 50 to 1000 stars; open clusters appear along the mainband of the Milky Way. Globular Cluster – A collection of 100000 to a million stars, arranged in a distinctive spherical shape; globular clusters appear around the centre of the Milky Way. Supercluster – A gigantic cluster of 4 to 25 clusters of galaxies, which is hundreds of millions of light-years in size. Redshift – The effect in which objects moving away from an observer have their wavelengths lengthened, toward the red end of the visible spectrum. Blueshift – The effect in which objects moving toward an observer have their wavelengths shortened, toward the blue end of the visible spectrum. Big Bang – The event that may have triggered the expansion of the universe 14 billion years ago. Dark Matter – The most abundant form of matter in the universe, invisible to telescopes. Dark Energy – A form of energy that makes up nearly three quarters of the universe; has the effect of increasing the expansion of the universe.