Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Intro to Astronomy Looking at Our Space Neighborhood Astronomy: The Original Science • Ancient cultures used the movement of stars, planets and the moon to mark time • Astronomy: the study of the universe • This led to the development of the first calendar – Year: Earth orbits the sun one time (365.25 days) – Month: about one orbit of the moon around Earth (29.25 days) – Day: one rotation of Earth on its axis Who’s Who of Early Astronomy • Ptolemy – 140 A.D. – Greek astronomer – Thought Earth was at the center of the universe and other planets & the sun revolved around it – Incorrect, but predicted motion of planets better than anyone else had • Copernicus – 1543 A.D. – Polish astronomer – Said the Sun was at the center of the universe and all planets orbit the sun – Very controversial! Not quickly accepted Who’s Who of Early Astronomy • Tycho Brahe – late 1500’s – Danish astronomer – Favored Ptolemy’s Earth-centered theory – Used tools to make detailed astronomical observations that helped future astronomers • Johannes Kepler – early 1600’s – Assistant to Tycho Brahe – Used Brahe’s data to show that all planets revolve around the sun in elliptical orbits – Gave three laws of planetary motion that are still used today Who’s Who of Early Astronomy • Galileo Galilei – 1609 – One of the first to use a telescope to see space – Discovered craters and mountains on the Moon and four of Jupiter’s moons – Showed that planets are not stars, but more similar to Earth • Sir Isaac Newton – 1687 – Showed that all objects in the universe attract each other by gravitational force (depends on mass & distance) – Explained why all planets orbit largest object – the Sun – Newton’s Cannon – why object orbit Earth Modern Astronomy • Edwin Hubble – 1924 – Astronomers thought our galaxy (Milky Way) included every object in space – Edwin proved the existence of other galaxies • New technology continues to improve our understanding of space • New galaxies, planets and moons are continually being discovered Earth’s Motion Early Astronomers’ First Focus How Does Earth’s Motion Affect Time? • Axis – the imaginary line that goes from the North to South Pole • Rotation – Earth’s spin on its axis (think of a top) – Earth’s rotation causes day and night – One rotation takes about 24 hours – 1 day! How Does Earth’s Motion Affect Time? • Revolution – Earth’s movement around the Sun – One revolution is one year – Earth’s path around the Sun is called its orbit – Earth’s orbit is an oval (ellipse), not a circle • 365.25 days (rotations) per year (revolution) ⁻ That’s why we have leap year every 4 years! How Does Earth’s Motion Affect Seasons? • 4 Seasons: summer, winter, spring, fall • Seasons in Northern Hemisphere happen at different times than Southern Hemisphere • Earth has seasons because its axis is tilted 23.5° as it moves around the sun The Moon Our Closest Neighbor in the Neighborhood Structure & Origin of the Moon • 3,476 km in diameter (about distance across the US) – ¼ the diameter of Earth • 1/8 the mass of Earth (less dense than Earth) • Collision Theory – suggests that an object about the size of Mars hit Earth and the scattered material formed the moon 4.5 billion years ago Features of the Moon • Galileo made the first detailed observations of moon’s features in 1609 with a telescope • Craters – pits that cover the surface, caused by impacts of meteoroids • Highlands – mountainous structures that cast large shadows • Marias –flat, dark areas that Galileo thought were oceans (maria = seas in Latin) – Low, dry areas that were flooded with molten rock billions of years ago Our Closest Neighbor • 384,400 km from Earth (about 30 Earth’s lined up) • Revolves around Earth as Earth revolves around the Sun • The positions of the moon, Earth and Sun cause the phases of the moon, eclipses and tides on Earth Motions of the Moon • Has its own axis – tilted 5° • Rotation (day): 27.3 Earth days • Revolution (year): 27.3 Earth days – So one year and one day on the moon are the same length! • Earth & moon have synchronous rotation – Near side of the moon always faces Earth – You never see the far side of the moon from Earth Phases of the Moon • The moon does not produce light – it reflects light from the sun • The shapes of the moon you see are called phases • Half of the moon is always lit, but sometimes Earth gets in the way • The phase of the moon you see depends on how much of the sunlit side of the moon faces Earth Cycle of Moon Phases • Start: New Moon – The lit side faces away from Earth so no moon is seen • Phases in Order: 1. New Moon 2. Waxing Crescent 3. First Quarter 4. Waxing Gibbous 5. Full Moon 6. Waning Gibbous 7. Third Quarter 8. Waning Crescent …then back to New Moon! • One complete cycle takes about 28 days (1 month) Eclipses • Eclipse: when moon’s shadow hits Earth or Earth’s shadow hits the moon • Two Types: (named for what is being blocked) – Solar – Lunar Solar Eclipses • When a new moon passes between Earth and the Sun, blocking light from reaching Earth • Total Solar Eclipses – where light is completely blocked by the moon – Only people in the darkest part of moon’s shadow (umbra) experience this • Partial Solar Eclipse – where part of the sun is visible; more common – People in the lighter part of moon’s shadow (penumbra) experience this Lunar Eclipses • Occurs at a full moon when Earth is directly between the moon and the sun, blocking light from reaching the moon • Earth’s shadow also has an umbra (darkness) and penumbra (partial darkness) • Total Lunar Eclipse - where light is completely blocked by the Earth – Can be seen anywhere on Earth where the moon is visible • Partial Lunar Eclipse - where the Sun, Earth and moon are not perfectly in line – moon passes partly into Earth’s umbra Tides • Tide – rise and fall of water every 12.5 hours • Caused by gravity pulling the moon and Earth together • Occur because of differences in how much the moon pulls on different parts of Earth (and the water on it) High & Low Tide • Water on Earth closer to the moon is pulled, forming high tide • Water on the other side of the planet has much weaker pull and resists due to inertia, forming another high tide • Low tides occur between the two high tides Spring & Neap Tides • Spring Tide: Occur when the moon, sun and Earth are in line – Gravity of sun and moon combine to produce greatest difference in high/low tide • Neap Tide: when the earth and sun are at right angles to earth and the moon – Produces a tide with the least difference between high/low tide – It’s like a tug of war between the sun and the moon!