Motions of Earth, the Moon, and Planets

The Earth’s Rotation West to East rotation (counter – clockwise) One full rotation each day Causes the apparent motion of the sun in the sky Causes day and night Notice the Earth is not straight up and it is in fact on a tilt. This tilt provides what to us? Who gets up earlier, newfounland or british columbia. Newfoundlad. Think about the time in which certain sport games are playing.

The Earth - Revolution One revolution takes 365.25 days Orbital radius: the average distance between an object in the Solar System and the Sun Why would you need an average? Earth is farthest from the Sun on July 4th Earth is closest to the Sun on January 3rd Why you need an average: because the Earth, like other planets is no always the same distance from the Sun. Furthermore it is on a tilt, this tilt is what causes the seasons for us. When the northern hemisphere is tilted toward the Sun it is summer, when the southern hemisphere is tilted toward the Sun it is summer there, and thus winter in the Northern hemisphere.

Question? Earth’s revolution period is 365.25 days per year? Then… what the heck is a leap year? How do they happen? Since Earth completes one revolution in 365.25 days, we fall ¼ of a day behind each year. The extra quarter days are added up as an extra day every four years. By adding a 366th day, our calendar year closesly matches the Earth’s revolution around the Sun February 29th, 2020.

Cool Fact Venus is the only planet in our solar system to rotate clockwise! Venus also has a longer day than year! How? A day on Venus lasts 243 Earth days, and this is longer than the 224.7 days it takes to orbit the Sun. - Every now and again on Venus you would have two birthdays in one day. Every 20 days you would have two birthdays.

Q: If the Earth is farthest from the Sun on July 4th… how are we experiencing summer and thus greater temperatures? Earth’s tilt: Earth’s rotational axis is tilted 23.5° Reasons for Earth’s seasons Although it is true that Earth’s distance from the Sun changes over the course of a year, the changes in Earth – Sun distance are not enough to cause the changes of the seasons. Season’s change primarily because of Earth’s tilt. Northern Hemispher tilted toward the Sun = summer, away from Sun = winter. So when northern hemisphere has winter, southern hemisphere has summer and vice versa

Solstice/ Equinox Solstice: when Earth’s tilt is most inclined toward or away from the Sun (longest day/ night of year) Equinox: when the hours of daylight equals the hours of darkness March Equinox – Vernal equinox September Equinox - Autumnal Equinox June 21 – longest day of the year (most sunlight) – Why?? December 22 – longest night of the year (least sunlight) – Why?? Ju

Video Earth’s rotation & revolution

Precession – Earth’s Wobble Wobble like a spinning top One full precession every 26, 000 years In 12,000 years the north pole will point to the star Vega. 26, 000 more years after that, it will point to Polaris again!

Motions of the Solar System Geo – means Earth Helio – means Sun Heliocentric model is what we have today Aristotle Cladius Plotemy Galileo Copernicus Why would someone believe the geocentric model is correct?

Why did ptolemy think the planets looped Why did ptolemy think the planets looped? Because if you track a planet over many many nights it appears as if the planets are moving backwards. When we pass the outer planets it may look like they are moving backward. Runners on a track, if your on the inside lane you are Earth, outside lanes are outer planets

What keeps the planets orbiting the Sun, and the Moon orbiting Earth? Gravitational force: the force of attraction between all masses in the Universe (gravity) Greater mass = greater gravitational force Sun’s gravitational pull keeps Earth in orbit Earth’s gravitational pull keeps the Moon in orbit Or you would spiral into the sun. Our distance and mass combined are perfect in terms of staying in orbit. Smaller mass would bring us out of orbit, greater mass would bring us spiraling into Earth.

What causes the Phases of the Moon? Moon like other objects in the Solar System, is illuminated by the Sun. However, the illuminated side does not always face the Earth. We see different parts of the moon as it resolves around the Earth 4 weeks = 1 full revolution of Earth. All phases of the Moon (8) make up the lunar cycle NOT caused by the Earth’s shadow. They are caused by how much of the Moon is illuminated by the Sun.

How does a full moon work, wouldn’t the earth be in the way How does a full moon work, wouldn’t the earth be in the way? Imagine light going onto a curved surface. Bring a flashlight.

Moon & Tides Tides: rising and falling of the surface of the oceans. Caused by gravitational pull of the Moon, and a tiny bit by the gravitational pull of the Sun The pull causes a bulge of water to form on the side of the Earth facing the moon, as well as on the opposite side of Earth where the moon’s force is the weakest (balance) 2 high tides and 2 low tides in 24 hours

High and low tides cause resulting movement of water High and low tides cause resulting movement of water. The other side of the Earth is effected as it requires balance.

Moon, the Sun, & Tides During new moon and full moon phases, the Sun, Moon, and Earth are aligned Combined gravitational force = high tides When the Moon & Sun are perpendicular = weaker tides

Question Where are the world’s highest tides located? Canada! – Bay of Fundy Can rise to the height of a four storey building Twice a day, 100 billion tones of water flow in and out of the bay November 2016 uses tidal energy to power up to 500 homes at this point. Imagine pushing someone on a swing: you gradually push them more and more but it becomes easier if you push them at the right time because they are already in motion. The period of oscillation – in which the bay of fundy’s water moves back and fourth (just like you swish water in a bath tub). Is in perfect sync with the Atlantic ocean tide flooding into the bay. So the ocean is like the person pushing the swing, and that it gradually pushed the tide more and more into the Bay each time. Shape of the bay also a factor.

Eclipses When one celestial object blocks the view of another celestial object from Earth Solar Eclipse: Moon between Earth and Sun, only possible during a new moon phase (rare) Lunar Eclipse: Earth is positioned between the Sun and the Moon, casting a shadow on the Moon.

When is the next solar eclipse visible from North America? Previously: 7 since 1950, none of which were entirely visible from St. Thomas.

August 21, 2017 – About 90% of the Sun will be covered

Homework Read 8.5 Pg. 328 1 – 6, 8, 13. For next Monday!