ladies and gentlemen boys and girls my name is jon pointer and welcome to another episode of the last science show uh now i know i haven't given a real introduction on why i am doing this but let's forget about that and dive right into today's lesson the earth sun and moon system [Music] the relative positions of earth the sun and the moon cause many of the phenomena experienced on earth lunar phases [Music] solar and lunar eclipses [Music] day and night and seasons are all the result of the earth sun moon system this tilt explains why the north pole experiences winter in january while the south pole is experiencing the opposite season summer the sun earth and moon make up a system of three celestial bodies that move in relation to each other the moon revolves around earth which revolves around the sun [Music] to put things in perspective here's the relative size of the sun the moon and the earth earth takes about 365.25 days to revolve once around the sun which is the length of our year how long does it take the earth to make one complete orbit around the sun 365 days or one year during earth's orbit around the sun it follows a nearly circular path but with a small elliptical eccentricity the sun is not in the center of the ellipse but one of the focal points you know what earth is it's our home planet it's where we live unless your skin is extremely green which means you're from mars [Music] uh you were born on earth this is your home planet the sun is the luminous star around which earth and other planets revolve is composed mainly of hydrogen and helium the sun is a star and it appears so large compared to the other stars because it is so much closer to us than any other star the solar system the solar system is the sun together with the group of planets and other celestial bodies that are held by the sun's gravitational attraction and revolve around it essentially the solar system is made up of the sun earth our moon other planets other moons asteroids and a plethora of other phenomena earth also rotates on its axis every 24 hours causing the cycle of day and night once again earth makes one complete rotation in 24 hours that means earth rotates 360 degrees in 24 hours or 15 degrees every hour earth is divided into 24 time zones because earth rotates counterclockwise east is later and west is earlier when it's 4 pm in chicago it's 5 pm in new york city earth rotation also causes the apparent motion of the sun rising in the east and setting in the west in addition this daily motion results in the illusion that the nighttime stars rise in the east and set in the west there is evidence that earth is constantly rotating it can be seen in focal's pendulum focal's pendulum is a free-swinging pendulum that would swing in the same direction if not for earth's rotation however since earth is constantly rotating that pendulum will never swing in the same direction because our earth's north pole is pointing to polaris the north pole star those stars closest to the pole star or circumpolar stars give the appearance of turning around the north star now just a few seconds ago i stressed the word illusion this daily motion results in the illusion that the nighttime stars rise in the east and set in the west we have to stress that it is an illusion for example in new york state stars appear to rise in the east and set in the west however the stars around polaris actually make a circle and do not rise or set let's define a star and no we aren't talking about denzel washington or jennifer lawrence or any other movie star like that a star is a self-luminous celestial body consisting of a mass of gas held together by its own gravity and which the energy is generated by nuclear reactions in its interior the revolution of the tilted earth causes the seasons of the years due to uneven heating of a tilted earth during summer the northern hemisphere is tilted toward the sun and receives direct rays during winter the northern hemisphere is tilted away from the sun and receives less sunlight this is why in most places on earth the climate changes throughout the year the tilt of earth during this revolution around the sun also causes the path of the sun through the sky to shift depending on the season during summer where earth's axis is tipped toward the sun the sun's apparent path in the sky is the highest and the weather is the hottest this results in longer hours of daylight during summer in contrast when earth is tipped away from the sun during winter the sun's path is lowest in the sky and there are fewer daylight hours and the coldest weather during spring and fall the sun's path is midway between summer and winter resulting in mild weather [Music] also during earth's revolution around the sun our view of the nighttime sky changes it is like walking around the edge of your living room observing what you have on your four walls during each season our view of the stars also changes because we point to a different direction in space except for those circumpolar constellations that are visible all year long each season brings a different set of constellations once again earth revolves around the sun in an elliptical orbit the sun is at one foci of the ellipse the shape of a planet's elliptical orbit is its eccentricity the more flattened the ellipse is the greater the value of its eccentricity the eccentricity of an elliptical orbit is a measure of the amount by which it deviates from a circle the closer a planet is to the sun in its orbit the faster it moves also planets closest to the sun revolve faster than the planets farther away in other words closer planets have a shorter year mercury's year is 88 days earth's is 365 days the length of your day depends on the season you are in in new york the day is approximately 16 hours at the summer solstice and only nine hours at the winter solstice at the equinoxes it is even at 12 hours a day and 12 hours of night the equator always has 12 and 12. the sun always illuminates half of the moon's surface however varying amounts of this illumination are visible from earth depending on the angle between earth the moon and the sun these eight monthly changes are called phases of the moon or the lunar cycle waxing crescent first quarter waxing gibbous full moon waning gibbous last quarter waning crescent and new moon let's break down those terms waxing and waning waxing no no no no not that type of waxing it means the illuminated side of the moon increases each day after the new moon for the next two weeks its phases are waxing halfway through its orbit is the full moon for the next two weeks its phases are waning this means the illuminated side of the moon decreases each day the phases of the moon are caused by the changing amount of the illuminated side of the moon that we see from earth a common misconception is that phases of the moon are caused by earth's shadow during a new moon the moon rises and sets during the day resulting in no visible moon at night for the next two weeks increasing amounts of the illuminated side of the moon become visible these phases are called waxing crescent first quarter waxing gibbous full moon as stated previously for the last two weeks of the lunar cycle a decreasing amount of the moon is visible calling the waning gibbous moon last quarter moon and ending with the waning crescent moon the cycle repeats with the new moon for solar and lunar eclipses to occur the sun the moon and earth must be positioned in a straight line in relation to each other [Music] an alignment of the sun moon earth results in a solar eclipse while an alignment of the sun earth moon results in a lunar eclipse although it appears bright in the night sky the moon produces no light of its own the light we see is reflected from the sun due to the moon's revolution around earth we see that light as different shapes called phases a lunar eclipse is when earth comes between the sun and moon on a full moon night the earth is the one casting the shadow we may see a partial lunar eclipse or a total lunar eclipse this can be seen from anywhere on earth where it's night and will last for several hours for about an hour the moon will appear red because of the sunlight bending around the earth this is where the term blood moon comes from and the three spheres are lined up earth casts a shadow on the moon when this occurs the entire night side of earth is able to witness the event if the moon falls into the umbra it will turn red from the bending of the longest light waves which are red from the sun around earth if it falls in the penumbra it will not be a total eclipse and not turn red a solar eclipse is when the moon blocks sunlight and casts a shadow on a small part of earth resulting in a solar eclipse for either eclipse to occur the sun earth moon system must be in a straight line during a solar eclipse the moon passes in between the sun and earth casting a small shadow on earth this small shadow the umbra is typically only about 100 miles in diameter and may be visible to only a small portion of the world a large part of earth will be in the penumbra and get to see a partial eclipse of the sun which will only be able to be viewed with special filters did you know that tides are the result of gravitational forces of the moon and to a lesser extent the sun a tide is the daily rise and fall of oceans that cover about 70 percent of earth its main effect is on the time and place the tides occur thus waves form on the ocean surface of varying heights the current depth and the shape of the coastline will also determine the power of the waves which helps to explain why tides are usually semi-diurnal with two high waters and two low walls well in some places there is just the one daily tidal cycle high and low tides are caused by the moon the moon's gravitational pull generates something called the tidal force the tidal force causes earth and its water to bulge out on the side closest to the moon and the side farthest from the moon these bulges of water are high tides as the earth rotates your region of earth passes through both of these bulges each day when you're in one of the bulges you experience a high tide when you're not in one of the bulges you experience a low tide this cycle of two high tides and two low tides occurs most days on most of the coastlines of the world tides are really all about gravity and when we're talking about the daily tides it's the moon's gravity that's causing them now gravity is too strong and too forceful no pun intended to talk about in just a few minutes we plan to have an entire episode dedicated to just gravity but for today let's do our recap earth rotates on an imaginary axis that runs through its pole earth's rotation gives us our day earth makes one complete rotation in 24 hours 15 degrees every hour we learned that there is evidence that earth rotates focal's pendulum showed us that although stars appear to rise in the east and set in the west the stars around polaris actually make a circle and do not rise or set earth is divided into 24 time zones because earth rotates counterclockwise east is later and west is earlier when it's 4 pm in chicago it's 5 pm in new york city earth revolves around the sun in an elliptical orbit the orientation of earth's axis changes with relation to the sun throughout the year and the altitude of the sun in the sky changes because of this this gives us our seasons the length of our day depends on the season we are in the moon produces no light of its own the light we see is reflected from the sun the movement of the earth and moon in relation to the sun causes solar and lunar eclipses during an eclipse either the earth or the moon move in front of the sun blocking the light and casting a shadow in space eclipses only occur when the sun earth and moon are in a straight line a solar eclipse occurs when the moon passes between the sun and the earth a lunar eclipse occurs when the moon passes through earth's shadow a tide is the daily rise and fall of oceans that cover about 70 percent of earth tides are the result of gravitational forces of the moon and to a lesser extent the sun well that was a lot we sure hope you enjoyed this extensive episode of the last science show where we discuss the sun moon and earth system make sure to subscribe like comment and share for more videos we'll see you next time so good morning good afternoon good evening and good science [Music]