Intro to Astronomy. Looking at Our Space Neighborhood

Transcription

1 Intro to Astronomy Looking at Our Space Neighborhood

2 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 ( days) Month: about one orbit of the moon around Earth (29.25 days) Day: one rotation of Earth on its axis

3 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

4 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

5 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

6 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

7 Earth s Motion Early Astronomers First Focus

8 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!

9 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 days (rotations) per year (revolution) That s why we have leap year every 4 years!

10 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

11 The Moon Our Closest Neighbor in the Neighborhood

12 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

13 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

14 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

15 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

16 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

17 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)

18 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

19 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

20 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

21 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)

22 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

23 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!