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Download Core Theme 3: The Solar System
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Core Theme 3: The Solar System Solar system: The Sun as part of the Solar System; eclipses and effects on Earth; planets, dwarf planets and other members of the Solar System (asteroids, comets etc.). What are these? Distances, scales, extent, history of mankind’s developing thought on our place in the Universe. Solar System Our neighbourhood Sun; 8 planets; dwarf planets; asteroids between Mars and Jupiter; trans-Neptunian objects and Oort cloud. Planets roughly spherical, orbits are usually elliptical. Resources http://www.esa.int/esa-mmg/mmg.pl? b=b&topic=Sun&subtopic=Solar%20wind&start=3 http://www.bbc.co.uk/science/space/solarsystem Relationships between Earth, Moon and Sun Moon orbits the Earth and shows phases Together they revolve around the Sun Day and Night, Seasons and Eclipses happen, aurorae etc. Eclipses: Lunar Eclipse: when the full Moon moves into the shadow of the Earth, cutting out the Moon’s normally bright, reflected sunlight. Demo and practice 4 There will be some Penumbral lunar eclipses coming up, but as the Moon will not pass through the main part of the Earth's shadow, there is not much to see, and if you didn't know that an eclipse was taking place you would not be aware of it. So we will have to wait for a decent lunar eclipse until the early morning of September 28, 2015. The next good lunar eclipses after that are on July 27, 2018 and January 21, 2019. http://eclipse.gsfc.nasa.gov/eclipse.html Solar Eclipse: when the whole Sun or part of the Sun is blocked out (or occulted) by the new Moon as seen from Earth. Can be either total, annular or partial. Demo and practice 7 Seasons result from the tilt in Earth’s axis and change in angle of sunlight falling on us during the year. DEMO 9 http://en.wikipedia.org/wiki/List_of_solar_eclipses_visible_from_the_United_Kingdom_AD_1000–2090 The “Small Bodies” Asteroids – small rocky, icy and metallic bodies of the inner solar system that mainly orbit in the asteroid belt between Mars and Jupiter. Range in size from tens of metres up to 1000 kilometres. Hundreds of millions of small bodies. Ceres is the largest asteroid, and like Pluto is classified as a dwarf planet. It makes up a third of the mass of the whole asteroid belt! Most known asteroids are just a few kilometres across. Sometimes Earth-approaching asteroids are in the news (e.g. on 8th November 2011 an object passed closer than the Moon, at just 0.85 lunar distances). Usually (hopefully!) they miss the Earth. Asteroid “Vesta” (top) and Comet McNaught (bottom) 12 Comets A comet is a small dust-and-ice body (“a dirty snowball”): a weakly bound collection of dust, ice and small rocky particles. The central “nucleus” can range in diameter from approximately a kilometre (km) up to many tens of km or more. Comets have been observed since ancient times and have traditionally been considered bad omens. When close enough to the Sun, comets show a visible “head” or coma (a thin, fuzzy, temporary atmosphere) and sometimes one or two tails. These are much larger structures, millions of km across or hundreds of millions of km in length. They are distinguished from asteroids by presence of a coma or a tail. Comets have a wide range of orbital periods, ranging from years up to millions of years. Short-period comets (periods less than 200 years) originate in both the Edgeworth-Kuiper belt (EKB), a region beyond Neptune ranging up to 60 AU from the Sun, and the Oort cloud (1,000 to 200,000 AU) Long-period comets originate in the Oort cloud. It is a nearly spherical swarm of more than 100,000 million comets with elliptical orbits extending up to halfway to the nearest star. While the asteroid belt is composed largely of rocky or metal objects, EKB and Oort cloud objects are mostly icy, comprising dust and frozen volatiles such as water, methane, carbon dioxide and ammonia (termed "ices”). Other Solar System Facts The origin and evolution of the Solar System began approximately 4,567 million years ago (4.567 billion years) with the gravitational collapse of a small part of a giant molecular cloud. The Universe is roughly three times older, i.e. approximately 13.7 billion years. Most of the collapsing material collected at the centre to form the Sun, while the rest flattened into a protoplanetary disk from which the planets, moons, asteroids, and other small Solar System bodies formed. In roughly 5 billion years, the Sun will cool and balloon outwards to many times its current diameter (becoming a red giant), before casting off its outer layers as a planetary nebula and finally leaving behind a stellar remnant known as a white dwarf. Meteor shower A meteor shower is a celestial event in which a number of meteors are observed to radiate from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extremely high speeds. Most meteors are smaller than a grain of sand, so almost all of them disintegrate and never hit the Earth's surface. Intense or unusual meteor showers are known as meteor outbursts and meteor storms, which may produce greater than 1,000 meteors an hour. Distance, Size and Scale Earth is approximately 150,000,000 km (150 million km) from Sun. Astronomers call this standard Earth-Sun distance 1 Astronomical Unit (AU). Earth is approximately 100 times smaller than Sun in diameter; the Moon is approximately 4 times smaller than the Earth. So 4 Moons would just fit across the Earth, and 400 Moons would just fit across the Sun. The Moon is roughly 384,400 km from Earth. Coincidentally, this is 400 times smaller than 1 Astronomical Unit, so the Moon can just cover the Sun as seen from Earth − making a total eclipse possible! Gravity on Moon = 1/6th that on Earth, so you would be 6 times lighter on the Moon! (Cola cans) The most distant known planet, Neptune, is 30 AU from the Sun; the EKB is 40–60 AU; and the Oort Cloud ranges from 1,000 AU to 200,000 AU . Let’s build a scale model of the solar system together; see worksheet A practical activity spaced over 100m in the playground Huge Distances For greater distances we use the speed of light to measure the immense distances in space. Light travels through empty space at nearly 300,000 km per second. Therefore in one year it can travel nearly 10 million, million km. We call this distance 1 light year (LY): the distance light travels in one year. Our Milky Way galaxy is roughly 100,000 LY across! The next nearest galaxy is more than 2 million LY away. Our Place in the Universe Galaxy: Milky Way: contains approximately 200,000 million stars, in a flattened disc-like structure 100,000 light years across. Our Solar System orbits the Galactic Centre every 250 million years: a “Galactic year”. Another galaxy: Andromeda nebula (picture, beautiful and inspiring). Can be seen with naked eye, 2.5 million LY away. We may be able to spot it tonight – in which constellation? Hubble Deep Field: image showing lots of other galaxies billions of LY away. Astronomers estimate that there are hundreds of billions of galaxies in the known Universe. Putting all our previous information together now!! Galilean moons Activity to spot them Kepler’s Laws on the HO History of mankind’s developing thought on our place in the Universe Since early times, man has been fascinated with discovering the origins of the cosmos. Similarly, man has often been influenced by his creationist ideas: that some divine power created the universe and everything in it. For example, the Ancient Greeks developed some of the earliest recorded theories of the origin of the universe. Unfortunately, many of these Greek philosophers and astronomers placed the Earth in the center of their models of the universe. They thought, if the heavens are divine, and the gods created man, well then certainly the universe must be geocentric, meaning the Earth is the center of the universe. Ancient societies were obsessed with the idea that God must have placed humans at the center of the cosmos (a way of referring to the universe). An astronomer named Eudoxus created the first model of a geocentric universe around 380 B.C. Eudoxus designed his model of the universe as a series of cosmic spheres containing the stars, the sun, and the moon all built around the Earth at its center. Unfortunately, as the Greeks continued to explore the motion of the sun, the moon, and the other planets, it became increasingly apparent that their geocentric models could not accurately nor easily predict the motion of the other planets. After Aristotle developed a more intricate geocentric model (which was later refined by Ptolemy), general cosmology clung to these misconstrued ideas for the next 2,000 years. Even when Nicholas Copernicus introduced the notion of a heliocentric universe, many contemporary societies greatly influenced by religious beliefs refused to accept it. Today we consider this a ridiculous question; we can directly observe that the Earth and the other planets in our solar system orbit around the sun. It is obvious that the technological advancements of the 20th century have allowed us to look out to the farthest corners of the visible universe, but our past history of erroneous assumptions should make us cautious. As we discover more and more about the origins of our early universe, we should realize that our present theories must be continually tested and modified because new theories frequently arise as we learn more through our observations. That is why most physicists and astronomers today are so inclined to accept the Big Bang Theory as the most plausible explanation for the origin of the universe. It puts together so many of the pieces of how the universe came into being, and seems to correct so many of the flaws found in previous theories. Until the 1920s, cosmology was still dominated by the theory of a Steady State Universe, or the idea that the universe was homogeneous (has the same general make-up throughout), infinite (that the universe just extends forever), and static (the universe is not expanding, it just is). If you just study the night sky, it seems easy just to think that this is the way the universe has always looked and will always look. In the 20th century, however, observations of the universe did not seem to add up with Steady State theory