ASTRONOMY The Sun-Earth-Moon System

Section 1: Earth

Properties of the Earth Earth is a sphere – round 3-D object Rotation – spinning of the Earth on its axis Axis – imaginary vertical line around which the earth spins Rotation causes day and night to occur

Properties of the Earth Magnetic Field – movement of material inside Earth’s core, along with Earth’s rotation, generates a magnetic field Helps protect us from harmful solar radiation by trapping charged particles from the Sun

Properties of the Earth Magnetic Axis – the magnetic axis is set at an angle of 11.5° from the rotational axis A compass needle points to the magnetic north pole, not the rotational north pole Declination refers to the difference between magnetic north and geographic north on a map

11.5°

What causes changing seasons? Orbiting the Sun Revolution – Earth’s yearly orbit around the Sun Earth’s orbit is not spherical, it is an ellipse – an elongated, closed sphere The sun in not in the center, but towards one end of the ellipse Closest: 147 million km away – Jan. 3 Farthest: 152 million km away – July 4

What causes changing seasons? A Tilted Axis Earth’s axis is tilted 23.5° from the perpendicular This tilt causes the seasons The hemisphere tilted toward the sun receives more sunlight than the hemisphere that is tilted away from the sun

What causes changing seasons Radiation from the Sun Hemisphere tilted toward the sun receives more direct rays from the sun, thus more solar radiation than hemisphere tilted away from the Sun

Solstices Solstice – the day when the Sun reaches its greatest distance north or south of the equator Northern hemisphere: Summer solstice – June 21 or 22 Winter solstice – December 21 or 22 Southern hemisphere: Summer solstice – December 21 or 22 Winter solstice – June 21 or 22 After the summer solstice the days get shorter; after the winter solstice the days get longer (winter solstice nearly the shortest day of the year)

Equinox Occurs when the sun is directly above the Earth’s equator Occurs in the spring (March 20 or 21) and autumn (September 22 or 23) During an equinox, the daylight hours and nighttime hours are nearly equal all over world

Section 2: The Moon – Earth’s Satellite

Motions of the Moon Rotation and Revolution Moon rotates on its axis and revolves around the Earth The moon’s rotation takes 27.3 days – the same amount of time it takes to revolve once around the Earth The same side of the moon always faces the earth

Phases of the Moon Moon phases – the different forms that the Moon takes in its appearance from Earth New Moon – occurs when the Moon is between Earth and the Sun Dark side faces the Earth Full Moon – occurs when all of the Moon’s surface facing Earth reflects light

Phases of the Moon Waxing Phases – occurs after a new moon, where you see more of the illuminated half of the moon each night Waxing crescent – less than half illuminated 1st quarter – right half illuminated Waxing gibbous (gibbous means “humpbacked”) – more than half illuminated

Waxing crescent 1st quarter Waxing gibbous

Phases of the Moon Waning Phases – occurs after a full moon, where you see less of the illuminated half every night Waning gibbous – more than half illuminated 3rd Quarter – left half illuminated Waning crescent – less than half illuminated

Waning gibbous 3rd quarter Waning crescent

Third

Eclipses Solar eclipse – occurs when the Moon moves directly between the Sun and Earth, and casts its shadow over part of the earth The revolution of the Moon causes eclipses – Moon’s shadow falls on the earth Lunar eclipse – during a full moon, when the Earth’s shadow is cast onto the Moon Only occur a few times each year

Eclipses Eclipses of the Sun Parts of an eclipse: Umbra – darkest portion of the Moon’s shadow (person standing in umbra is in a full solar eclipse) Penumbra – lighter shadow on Earth’s surface (person standing in penumbra is in a partial solar eclipse)

Eclipses Eclipses of the Moon Lunar eclipse – when the Earth’s shadow falls on the Moon Starts when Moon moves into Earth’s penumbra (curved shadow on Moon) When completely in Earth’s umbra, Moon goes dark – sometimes sunlight bent through Earth’s atmosphere make Moon appear red

The Moon’s Surface Crater – depression in the Moon’s surface cause by meteorites, asteroids and comets striking the surface After impact, lava from within the Moon filled these craters Maria – the resulting dark, flat regions on the surface

The Moon’s Origins Many different theories: Moon captured by Earth’s gravity Material surrounding the Earth condensed to produce the Moon Earth ejected molten material that became the Moon The Impact Theory – Mars-sized object collided with earth, ejected material into space and the particles joined together to create the Moon

Section 3: Exploring Earth’s Moon

Surveying the Moon Impact Basins – impact crater – depression left by an object striking the Moon South Pole-Aitken Basin – oldest identifiable impact feature on Moon’s surface In the shadow most of the time, thought to contain ice deposits