Earth and Moon Chapter 19 PS 1, PS7 (S.8.7.1, S.8.7.2, S.8.7.3)
ESSENTIAL QUESTIONS WHAT IS THE EARTH’S POSITION IN SPACE RELATIVE TO THE SUN AND MOON? HOW DOES THIS POSITIONING AFFECT VARIOUS PHENOMENA?
EARTH FACTS • The Earth is an oblate spheroid. • Eratosthenes was the Greek astronomer who computed the circumference of the Earth by assuming that it was a perfect sphere. How did he do this? Was he very accurate? • The diameter at the equator is40,075.16 km and 40,008 km from pole to pole. What causes this variation? • The distance from the Earth to the Sun is 150,000,000 km (1 Astronomical Unit or AU)
The Earth-Sun System • It takes one year or 365.25 days for the Earth to revolve once around the Sun • It takes the Earth 23 hours and 56 minutes to rotate once on its axis • The Earth’s rotation causes day and night • The side of the Earth facing the Sun gets light (daytime), the side that faces away from the Sun is without light (nighttime).
The Seasons • Seasons are caused by the tilt (angle) of the Earth, and the path it takes around the sun • It is warmer near the equator because sunlight hits the Earth’s surface more directly than at higher latitudes
Earth’s Tilt & Revolution • Seasons are caused mainly by the 23.5 degree tilt of the Earth’s axis. • This tilt causes the number of daylight hours to change depending on the time of year. • During winter, there are fewer daylight hours in in the Northern Hemisphere because it is tilted away from the sun. • During summer, there are more daylight hours because the Northern Hemisphere it tilted toward the Sun. • The path of REVOLUTION is elliptical. The point at which the Earth is closest is called its perihelion. The point at which it is farthest away is called its aphelion. The distance from the sun does not determine seasonal change. It is the way the Earth revolves around the sun that affects the angle of the Earth to the Sun which in turn causes the seasonal variation.
The season’s yearly cycle • An Equinox occurs when the Sun is directly above the equator and both hemispheres receive the same amount of sunlight. This happens in March and September (Vernal and Autumnal). First day of? • A Solstice is the time when the sun is the farthest north or south from the Equator. • During the Summer Solstice, the Northern Hemisphere is tilted toward the sun and receives more warmth and daylight. The Summer Solstice occurs in June and is the longest day of the year. First day of? • During Winter Solstice, the Northern Hemisphere is tilted away from the sun and receives less warmth and daylight. The Winter Solstice occurs in December and is the shortest day of the year. First day of?
HELPFUL WEBSITES WWW.NASA.GOV
Earth/Moon System • Lunar Cycles (phases) • Eclipses • Tides
Lunar Cycles • Waxing- the sunlit part of the moon gets larger • Waning- the sunlit part of the moon gets smaller
An eclipse happens when the shadow of one celestial body falls on another body. An eclipse can only occur at a new or full Moon and only when the Sun, Moon, and Earth are at certain orbital positions during what is called an eclipse season. Eclipse seasons occur every 173 days ( about 2X a calendar year) and last for 30-40 days. Each season has two eclipses – solar and then, about two weeks later a lunar. Eclipses • A Lunar eclipse happens when the Earth comes between the sun and the moon. • A Solar eclipse happens when the moon comes between the Earth and the Sun. Annular eclipses happen when the moon does not cover the sun completely and a “ring of fire” encircles the moon.
The Moon and the Tides • On the side of Earth that faces the moon the ocean’s surface bulges because of the moon’s gravity pull on the water. • On the opposite side of the Earth, the water bulges because of the rotation of the Earth and the revolution of the moon around the Earth.
The Sun and the tides • The Sun’s gravity also pulls on the Earth and affects the tides, however since the Sun is much farther away than the moon, its affect is about half that of the moon. • Tidal Range- the difference between levels of ocean water at high tide and low tide.
Moon’s phases and the tide • Spring Tides- Occur when the Sun, Earth, and Moon are in line. The Sun’s added gravitational force cause the greatest tidal range between high tide and low tide. • Neap Tides- Occur when the Sun, Earth and Moon form a 90 degree angle. These tides have the smallest range, because the gravity of the Sun and Moon are working in different directions. Why Tides?
WORKS CITED http://www.sfgate.com/getoutside/1996/jun/tides.html WWW.NASA.GOV WWW.UCAR.EDU