Planetary Science- Part 1

I. Round Earth-Flat Earth A. Sailing Ships 1. The horizon is where the sky and Earth appear to meet. 2. Your line of sight is the straight path taken by light from an object to your eye. 3. Ships sailing out to sea appear to sink on the horizon. 4. If the Earth were flat, you’d see the entire ship out on the horizon.

What does the ship appear to be doing? HORIZON

B. Shadow Evidence 1. Eratosthenes found the circumference of the Earth using sticks, shadows, some geometry, and feet! 2. Light rays travel in straight lines. 3. Because the Sun is so large and so far away, all rays of light hitting anywhere on Earth are parallel to one another. 4. A pole only casts a shadow when the sun shines on its side, not on its top. 5. Poles on a curved surface cast shadows of different lengths.

6. The shadows are longer at higher latitudes. 7 6. The shadows are longer at higher latitudes. 7. Local noon is when the sun is directly overhead in the sky (does not mean 12pm noon!) 8. Shadows in winter are longer than shadows in summer due to the changes in the angle of the sun.

II. Day and Night 1. Earth rotates, or spins on its axis in a counter-clockwise direction. (West to East) 2. Day and night are a result of rotation. 3. The sun appears to move across the sky from east to west due to Earth’s rotation. 4. Shadows change during the day due to the changing position of the sun in the sky. 5. The sun is a source of light that illuminates Earth during the day.

6. When light falls on a spherical object, like a planet, exactly half is in the light and half is in the dark. 7. The Earth rotates on its axis once every 24 hours, giving the illusion of a sun that rises and sets. 8. One complete rotation of our planet describes one complete day. One rotation of Earth is one day, or about 24 hours.

III. Seasons 2. The tilted axis –23.5° gives us seasons. 1. The earth revolves (orbits) around the sun—about 365 1/4 days—one year. 2. The tilted axis –23.5° gives us seasons. 3. The angle of sunlight affects temperature--the more direct the angle of sunlight the warmer it is. The angle varies due to Earth's spherical shape. Ex. It is warmer at the equator because it gets more direct sunlight, and cooler at the poles because the sunlight is at an angle. 4. Earth's tilt affects not only the intensity of sunlight falling on earth, but also the number of daylight hours. 5. The number of daylight hours changes from season to season.

The map shows where solar power works best in the United States The map shows where solar power works best in the United States. The places in the map that are color blue get the least amount of sun. The places with red get the most amount. This means that the red places are the best locations to use solar electricity.

Where would you put your solar panels?

6. In the No. Hemisphere around June 21 is longest day of year 6. In the No. Hemisphere around June 21 is longest day of year. This is called the Summer Solstice. 7. In the No. Hemisphere around December 21 is the shortest day of the year. This is called the Winter Solstice. 8. The Vernal Equinox, or Spring is around March 21 and the Autumnal Equinox, or Fall is around September 21. Sunlight spreads evenly across equator and there is about 12 hours of day and night across the globe. The amount of daylight varies due to refraction of light in the atmosphere. 9. The Earth is actually a little closer to the sun in its orbit during winter. This is called perihelion. 10. The Earth is a little further from the sun in summer. This is called aphelion.

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