The Earth In Space

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The Earth In Space

• Why do we have night and day?
• Why do daylengths change?

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Understanding Night and Day

• Day and night is the absence or presence of
  sunlight shining on the surface of the globe!
• It is caused by the spinning of the Earth on its
  axis
• There are some strange things that you should be
  aware of, as well as what causes them!

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The tilt of the Earth

• The Earth spins on an axis. This is an imaginary
  line running through the middle of the Earth from
  North to South pole.
• The important thing to note about the axis, is
  that it is tilted 23.5o from the vertical.
• The tilt causes different daylengths depending on
  latitude on the Earths surface
• The following animation demonstrates this. The
  coloured dots represent locations on the surface
  of the Earth that are in the same time zone.

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12 midnight
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2am
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3am
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4am
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6am
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8am
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10am
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12 noon
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2pm
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3pm
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4pm
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7pm
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9pm
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11pm
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12 midnight
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2am
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3am
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4am
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6am
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8am
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10am
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12 noon
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2pm
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3pm
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4pm
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7pm
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9pm
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11pm
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12 midnight
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2am
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3am
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4am
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6am
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8am
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10am
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12 noon
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2pm
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3pm
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4pm
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7pm
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9pm
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11pm
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12 midnight
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2am
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3am
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4am
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6am
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8am
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10am
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12 noon
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2pm
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3pm
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4pm
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7pm
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9pm
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11pm
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So, what did you see?

• The animation shows the Northern Hemisphere
  tilted towards the Sun. This is the position
  that it would be in on the Summer Solstice (21
  June)
• What do you notice about the blue circle?
• What do you notice about the red circle?
• What would happen to daylength if the green dot
  moved north?
• What would happen to daylength if the green dot
  moved south?
• How would the diagram be different if the
  Southern Hemisphere was tilted towards the Sun?
  When would this happen?

Click to run animation again
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East and West
How does the Sun appear to move across the sky
during the day?
NOON is when the Sun is HIGHEST in the sky.
Because the Earth SPINS, the Sun moves across the
sky.
The Sun RISES in the EAST.
The Sun SETS in the WEST.
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Length of Day
The Sun is at a higher angle in the sky in summer
than in winter. This means the Sun is ABOVE THE
HORIZON longer in summer than in winter. So, in
summer, the days are longer and the nights are
shorter, compared to winter.
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Seasons

• We have seen that on any given day, the amount of
  daylight varies between different locations on
  the Earths surface
• However, even at a single location the length of
  daylight varies over a year
• This is as a result of the Earths orbit around
  the Sun
• This also results in the Seasons

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Seasons (2)

• You might expect that the reason it is warmer in
  the Summer is because we are closest to the Sun
  at this point
• However, at Summer and Winter the Earth is at its
  two furthest points from the Sun
• The Earth is nearest the Sun at the Spring
  equinox and the Autumn equinox

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Terms to remember

• Summer solstice longest day ( approximately the
  21 June)
• Winter solstice shortest day (approximately the
  21 December)
• Equinox daytime is same length as night time.

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The path of the Earth round the Sun
June
June
Northern hemisphere points away from the
Sun Shorter days ? Colder Winter in North.
Summer in South
Northern hemisphere points away from the
Sun Shorter days ? Colder Winter in North.
Summer in South
December
December
It takes 365.25 days for Earth to orbit the Sun.
Because of the .25 day, we add an extra day to
our year every four years a leap year.
North and South getting equal amounts of
sunlight Autumn in North. Spring in South
North and South getting equal amounts of
sunlight Autumn in North. Spring in South
October
October
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• Why is it summer when the northern hemisphere is
  tilted towards the Sun?

• When the northern hemisphere is tilted towards
  the Sun, the Sun is at a higher angle in the sky
  and the Suns rays are less spread out. They have
  a greater heating effect.
• In northern winter the Sun is at a lower angle in
  the sky because the northern hemisphere is tilted
  away from the Sun. The Suns rays are more spread
  out and have a lower heating effect than in
  summer.
• Dont forget that there are also longer days when
  it is summer, so there is more time for the Sun
  to warm the Northern hemisphere

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