Earth Moon and Sun Astronomy Unit Earth in

Earth, Moon, and Sun Astronomy Unit

Earth in Space • Astronomy- the study of the moon, stars, and other objects in space • Axis- an imaginary line that passes through Earth’s center and the North and South poles, about which Earth rotates • Rotation- the spinning motion of a planet about its axis

• Earth’s rotation on its axis causes day and night. • Revolution- movement of one object around another object • One complete revolution around the sun is called a year. • Orbit- the path of an object as it revolves around another object in space

Seasons on Earth • If Earth’s axis were straight up and down relative to the sun, temperatures would remain fairly constant. There would be no seasons. • Earth has seasons because its axis is tilted as it moves around the sun.

• Latitude- measurement of distance from the equator, expressed in degrees north or south • Solstice- the two days of the year on which the noon sun is directly overhead at either 23. 5 degrees south or north • When the noon sun is overhead at 23. 5 degrees south, it’s winter in the northern hemisphere.

• When the noon sun is overhead at 23. 5 degrees north, it’s summer in the northern hemisphere. • Equinox- the days of the year on which neither hemisphere is tilted toward or away from the sun • Vernal equinox- day of the year (March 21) that marks the beginning of spring in the northern hemisphere

• Autumnal equinox- day of the year (September 23) that marks the beginning of fall on the northern hemisphere • Seasonal changes affects living things in the United States. • In spring and summer, the sun shines for more hours each day and the sun is higher in the sky.

• The warmer days allow plants to grow leaves and flowers. • In the fall and winter, the nights get longer and plants stop growing and lose their leaves and flowers.

The Sun’s Interior • The interior of the sun is like a giant furnace. • The sun produces energy from nuclear fusion. • Nuclear fusion- process by which hydrogen atoms join together to form helium, releasing energy. • This occurs only under conditions of extremely high temperatures and pressure.

Nuclear fusion occurs in the sun’s core, the central part of the sun.

The Sun’s Atmosphere • The sun’s atmosphere has 3 layers: the photosphere, the chromosphere, and the corona. • Photosphere- inner layer of the sun that makes light • Chromosphere- glow that comes from the middle layer of the sun during a total solar eclipse • Corona- outer layer of the sun that glows like a white halo around the sun

• Solar wind- a stream of electrically charged particles produced by the sun’s corona • Features on or above the sun’s surface include sunspots, prominences, and solar flares. • Sunspots- areas of gas on the sun that are cooler than the gases around them

• Cooler gases don’t give off as much light as hotter gases, which is why sunspots look darker than the rest of the photosphere. • Prominences- reddish loops of gas • Solar flares- an explosion of hydrogen gas from the sun’s surface that occurs when loops in sunspot regions suddenly connect

Comparing Earth to the Sun • The diameter of the Sun is 1, 392, 000 km, while the equatorial diameter of the Earth is 12, 756 km. Compared to the Earth the Sun is HUGE.

Comparing the Earth to the Moon The average distance between Earth and Moon is approximately 30 times Earth's diameter.

Comparing the Sun to the Moon • The Sun is 400 times the Moon's diameter and 400 times as far away. That means the Sun and Moon appear to be the same size when viewed from Earth.