Warm-up What causes the seasons on Earth?

Astronomy Sun, Earth and the Moon

What is Astronomy? Astronomy is the study of the universe

How is time defined? Year: time required for the Earth to orbit the Sun

How is time defined? Month: division of the year that is based on the orbit of the moon around the Earth

How is time defined? Day: the time required for Earth to rotate once on its axis

Light Year-The distance that light travels in one year.

Famous Astronomers: Copernicus 1473-1543 Polish heliocentric model: the earth rotates around the sun.

Famous Astronomers: Galilei Galileo Galilei 1564-1642 Italian Developed telescope, discovered moon features, experimented

Today - Many Different Types of Telescopes Objects in space emit radiation from all parts of the electromagnetic spectrum Radio Infrared Ultraviolet X rays Gamma rays The Very Large Array Radio Telescope in New Mexico, US

Electromagnetic spectrum

Famous Astronomers: Kepler Johannes Kepler 1571-1630 German Detailed planetary motion in 3 laws

Famous Astronomers: Newton Sir Isaac Newton 1643-1727 English Developed laws of gravity and motion

Famous Astronomers: Hubble Edwin Hubble 1889-1953 American Confirmed existence of galaxies beyond our Milky Way galaxy Andromeda Galaxy

How Do We Know About Space? Space is explored by humans using telescopes, satellites, probes and knowledge. Hubble Space Telescope uses many electromagnetic spectrum sensors Solar Dynamics Observatory focuses on the Sun

What Causes the Seasons? The tilt of the Earth’s axis as the planet is orbiting around the sun The part of Earth angled towards the Sun gets more direct radiation  summer!

What season would this be Seasons If the northern hemisphere is tilted towards the sun, then it receives more solar energy during the day than the southern hemisphere. What season would this be for North Carolina?

What season would this be Seasons If the northern hemisphere is tilted away from the sun, then it receives less solar energy during the day than the southern hemisphere. What season would this be for North Carolina?

How Much is the Tilt? The Sun’s rays hit the Earth at a more direct angle during summer than in winter The tilts also causes longer daylight than nighttime during summer

Solstices The days when the Earth’s tilt is at it’s maximum with regards to the Sun. Notice how the Sun’s rays directly hit: Tropic of Cancer during the summer solstice (A) Tropic of Capricorn during the winter solstice (B)

Equinoxes Equinox - when the sun passes directly over the equator The number of daylight hours equals the number of nighttime hours “equinox” means “equal nights” vernal equinox autumnal equinox

Precession Precession: change in direction of rotational axis – with no change in tilt (26,000 year cycle for Earth) Rotational axis slowly traces out a cone Due to nonspherical shape – Earth bulges outward at the equator Rotation axis is the line in red

Nutation The rocking, swaying or nodding motion in the axis of rotation of the Earth It is the wobble around the precession axis Precession axis is the line in white

Main cause: gravitational forces from the Moon, the Sun and the planets acting on Earth

Barycenter Center of gravity around which two or more bodies revolve

Barycenter of Solar System The Sun moves slightly as the gravitational pull of the planets tug on it as they rotate around the Sun.

The Moon No light source – what we see is the reflection of the Sun’s light Diameter of 2,000 miles Between 3.8 and 4.6 billion years old

No Wind or Weather No atmosphere – so surface temperatures of 127°C during day to -173°C at night (260°F to -280°F) Yikes! No atmosphere or flowing water means no erosion Neil Armstrong’s footprint will remain visible for 10 million years because there’s no erosion on the Moon

Impact Craters Has lots of impact craters – craters formed when objects from space crash into the lunar surface Earth had same bombardment of craters, but erosion erased evidence

Composition Very similar to Earth, though not identical – mostly silicates Iron poor – similar to Earth’s outer crust Apollo 11 mission in 1969

Formation: Impact Theory A Mars-sized object smashed into the Earth, spraying debris into orbit around the Earth The debris reformed into the Moon Also called “Ejected Ring” theory

Orbit As the Moon rotates around the Earth, it also rotates around its own axis, keeping the same side facing the Earth. We can never see the “back” of the Moon from the Earth. About 27 days for one orbit around the Earth

Phases of the Moon

Solar Eclipse Occurs when the Moon passes directly between the Sun and Earth, blocking our view of the Sun. Recall the Moon’s orbit is above and below the plane of the Earth and Sun, so the Moon does not often get between the Earth and the Sun

Lunar Eclipse Occurs when Moon passes through Earth’s shadow Only during full moon, when the Moon is on the opposite side of the Earth from the Sun