why do we have day and night video


It takes just over 365 days for the Earth to travel all the way around the Sun. We call the length of time it takes to go around the Sun a year, but to make life easier, most years have 365 days and every 4th year has 366 days. We call a year with 366 days a leap year. The extra day is February 29th. The year 2012 was a leap year, and 2016 and 2020 will also be leap years. The further you are from the equator, the longer a day will be in summer and the shorter it will be in winter. б On the longest day of the year in London there are about 16 hours and 39 minutes of daylight, but in Edinburgh, 400 miles north of London, there are 17 hours and 36 minutes of daylight. This is because Edinburgh is further away from the equator than London is. To help us know where we are in the world, we also divide the world into Eastern and Western hemispheres. The line between them is called the Prime Meridian and it runs through the Greenwich Royal Observatory in London. All measurements of how far East and West places are are taken from this line. We call these measurements longitude. Midday is the time in the EarthБs rotation when the position of the sun is at the same longitude. The sun has travelled half way across the sky and still has half way to travel. For people living on the far side of the world, when it is midday in London, it will be the middle of the night for them. It is more useful for them to set their clocks by when the sun will be visible where they live than when it will be visible in London.


For this reason we divide the world into Бtime zonesБ so that the time on the clock matches the position of the sun in the sky. Most time zones are set as an exact number of hours ahead of or behind the time in London. The time in France is one hour ahead of London and the time in New York in America is 5 hours behind London. Most countries prefer to be in only one time zone. That way all the schools and offices open and close at the same time and nobody gets confused. This means that the boundaries between time zones arenБt always straight so that all of the country is in one time zone, even though part of the country should be in another one. The USA is so big that it is in several time zones. On the far side of the world from Greenwich is the International Date Line. On the western side of the line the time is 12 hours ahead of London and on the eastern side of the line the time is 12 hours behind London. This means that on the western side of the line it is one day later than on the eastern side of the line. Sometimes we change the time of the clocks so that we can make more use of the hours of daylight. If we used the same time all year around in Britain then, in the summer, the sun would rise at 3:30am and set at 8:30pm. Not many people are awake at 3:30am, but lots of people are awake after 8:30pm. We set our clocks forward one hour in the spring so that the sun rises at 4:30am and sets at 9:30pm and we set them back one hour in the winter.

This is called summer time. Day Б This is the length of time it takes the Earth to spin all the way around so that you get a night and a day: 24 hours. Daytime Equator Equinox Ббdays when there are 12 hours of light and 12 hours of darkness everywhere on Earth. There are two each year Б one in late March and one in late September. International Date Line Б The line on the far side of the world from the Prime Meridian where the east and west sides of the line are in different days. Latitude Б This is a number between 0 and 90 that tells you how far from the equator you are. бThe latitude of the equator is 0б, and the latitude of the North Pole is 90б. Longitude Б This is a number between 0 and 180 that tells you how far from the Prime Meridian you are. The longitude of the Prime Meridian is 0б, and the longitude of the International Date Line is 180б. Nighttime North Pole Prime Meridian Б the line dividing the Eastern and Western hemisphere, running through Greenwich Royal Observatory in London
Seasons Б There are four seasons Б spring, summer, autumn and winter. Solstice Б The longest and shortest days of the year are the Summer Solstice and Winter Solstice. South Pole Time zone Б The Earth is divided into time zones. The time in most time zones is one hour earlier than the time in the zone to the East, and one hour later than the time in the zone to the West. Year Б the length of time it takes the Earth to travel around the Sun, approximately 365 days.

Now that we\’ve explored how the Earth and Sun are positioned in space, let\’s really focus on our key ideas: day and night. In the picture, we can see why day and night exist. The sun lights half the Earth (day) and not the other half (night). But what makes day turn into night? That\’s where rotation comes into play. You see, the Earth slowly rotates (or spins) around. This means that the half of Earth receiving sunlight now, will slowly spin around to the other side where there is only darkness. The same idea is true for the dark half. As the Earth rotates, it will slowly move into the area where the sun is hitting. When that happens night will turn to day! It\’s weird to think about because to us it seems like the Sun is rising and setting. But in reality, the Sun isn\’t moving at all. Instead, we are moving! You just don\’t notice because everything else on Earth is spinning around (or rotating) with you. When you wake up tomorrow morning, or go to sleep tonight, remember that the Earth is constantly spinning. The Earth is the planet we live on. This spinning movement is called rotation. The Earth rotates, or spins, around like a top. This rotating causes light from the Sun to light up different halves of the Earth. The Sun is our nearest star. The half of Earth being lit by the Sun experiences day, while the half that isn\’t lit experiences night. As the Earth rotates the lit and dark sides switch positions and day changes to night, or night changes to day.

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