Viewed from Earth's north pole, the rotation of Earth and its moon are counter-clockwise.!

Transcription

1

2 The Earth rotates around once in 24 hours The time it takes for the Earth to rotate completely around once is what we call a day. It's Earth's rotation that gives us night and day. Viewed from Earth's north pole, the rotation of Earth and its moon are counter-clockwise.!

3 Earth's orbit (path of revolution around the sun) is nearly circular, so that the difference between Earth's farthest point from the Sun and its closest point is very small. It takes roughly 365 days for the Earth to go around the Sun once. The time it takes for the Earth to go around the Sun one full time is what we call a year.

4 The combined effect of the Earth's orbit around the sun and the tilt of its axis result in the seasons.

5 Summer is NOT caused by the Earth being closer to the sun. Winter is NOT caused by the Earth being farther from the sun. Seasons are caused by the Earth s orbit and it s tilt. Summer in the northern hemisphere occurs at the same time as winter in the south, and vice-versa. * In fact, the Earth is furthest away from the Sun in June when it is summer in the northern hemisphere.

6 As the Earth travels around the Sun, it remains tipped in the same direction. This means that sometimes the northern half of the Earth is pointing towards the Sun (summer), and sometimes it is pointing away (winter). These points in the Earth's orbit are called solstices.

7 Notice that when the northern hemisphere is tilted towards the Sun, the southern hemisphere is tilted away. This explains why the hemispheres have opposite seasons. Northern Hemisphere Southern Hemisphere

8 Halfway in between the solstices, the Earth is neither tilted directly towards nor directly away from the Sun. At these times, called the equinoxes, both hemispheres receive roughly equal amounts of sunlight. Equinoxes mark the seasons of autumn and spring and are a transition between the two more extreme seasons, summer and winter.

9 The picture shows the view from the solar system of someone standing on the ground in Ohio during the summer solstice. The summer solstice, around June 21, occurs when the northern half of the Earth is tilted towards the Sun. Notice that the Sun is north of the equator.

10 The picture shows how the Sun moves through the sky for someone standing on the ground in Ohio during the summer solstice. The northern hemisphere is getting more direct sunlight, which heats the Earth most efficiently, than the southern hemisphere. This is summer for people in the northern hemisphere. During the summer, the Sun is also above the horizon longer than it is during the winter. The summer solstice is the longest day of the year.

11 The picture shows the view from the solar system of someone standing on the ground in Ohio during the winter solstice. The winter solstice, around December 21, occurs when the northern half of the Earth is tilted away from the Sun. Notice that the Sun is south of the equator. So, on the winter solstice, the northern hemisphere is getting less direct sunlight than the southern hemisphere. This is winter for people in the northern hemisphere.

12 The picture shows how the Sun moves through the sky for someone standing on the ground in Ohio during the winter solstice. During the winter, the Sun is also above the horizon for a shorter time than it is during the summer (the nights are long). The winter solstice is the shortest day of the year.

13 The picture shows the view from the solar system of someone standing on the ground in Ohio during an equinox. An equinox, around March 21 and September 21, occurs when neither half of the Earth points directly towards the Sun. In fact, the Sun is at the equator, so both halves of the Earth are getting about the same amount of sunlight.

14 The picture shows how the Sun moves through the sky for someone standing on the ground in Ohio during an equinox. Equinox literally means "equal night". On the vernal (spring) and autumnal (fall) equinoxes, day and night are the same length. Neither hemisphere gets more sunlight than the other, so both have similar seasons (fall in one hemisphere and spring in the other).

15 Equal amounts of daylight Longest amount of daylight Shortest amount of daylight Equal amounts of daylight

16 Spring in Northern Hemisphere because the earth is NOT tilted. Summer in Northern Hemisphere because the earth is tilted TOWARDS the sun. Winter in Northern Hemisphere because the earth is tilted AWAY from the sun. Fall in Northern Hemisphere because the earth is NOT tilted.

17 Seasons are caused by the Earth s orbit and it s tilt. NOT The distance from the sun.

18 Months were originally based on the time it takes the moon to orbit the earth = 29.5 days 29.5 days x 12 months = 354 days??? In 46 B.C., Julius Caesar ordered the calendar year to be 365 days in length and to contain 12 months. This forced some days to be added to some of the months to bring the total from 354 up to 365 days.

19 The orbital period of the Earth is days. Julius Caesar s calendar accounted for 365 days. To account for the extra days, every fourth year was made a leap year. This made the average length of a year to be days. Even the difference of an orbital year days and a calendar year of days was off. Eventually, Pope Gregory XIII created the Gregorian Calendar to account for the difference. The Gregorian Calendar accounts for years on a 400 year cycle.