Download Earth`s Days, Years, Seasons

EARTH’S DAYS,
YEARS, AND
SEASONS
W H AT
D ET E R M I N E S T H E
LENGTH OF A
D AY ?
• All planets spins on its axis
• Axis – imaginary straight line running from pole to pole
• Rotation – spinning of a body on its axis
• Day – the time it takes a planet to complete one full
rotation on its axis
– 1 day on Earth: 24 hours
• Only half the Earth faces the sun at a time
– Daytime
• The other half of the Earth faces away from the sun
– Nighttime
– 1 day on other planets does not equal 24 hours
W H AT
D ET E R M I N E S T H E
LENGTH OF A
YEAR?
• The Earth is traveling around the sun at nearly 30 km/s
• Revolution – motion of a body that travels around another body in
space
• Earth completes a full revolution around the sun in 365 ¼ days, or
about one year
– Every four years, we add the ¼ days and add one more day to February
• Leap year: February 29th
• Earth’s orbit is elliptical, or oval-shaped and not circular
– In January, Earth is 2.5 million km closer to the sun than it is in July
• This causes minimal changes in Earth’s temperature
W H AT C O N D I T I O N S
ARE AFFECTED BY
T H E T I LT O F
EARTH’S AXIS?
Earth’s axis is tilted at 23.5°
Axis always points towards the North Star
TEMPERATURE
• The angle at which the sun’s rays strike each part of Earth’s surface
changes as Earth moves in its orbit
– When the North Pole is tilted toward the sun, the sun’s rays strike the
Northern Hemisphere more directly
– This causes the Northern Hemisphere to receive a higher concentration of
sunlight, which makes it warmer
• Summer
– When the North Pole it tilted away from the sun, the sun’s rays strike the
Northern Hemisphere less directly
– This causes the Northern Hemisphere to receive a lesser concentration of
sunlight, which makes it colder
• Winter
TEMPERATURE CON’T
• The spherical shape of Earth also affects how the sun
warms up an area
– Temperatures are higher at areas where the sun directly hits the
Earth
– Temperatures are lower at areas where the sun hits the Earth at
an angle
DAYLIGHT HOURS
• All locations on Earth have an average of 12 hours of light
each day
• The actual number of daylight varies based on the time of
year and location
– Areas tilted towards the sun receive more hours of daylight
– Areas tilted away from the sun receive less hours of daylight
MIDNIGHT SUN
• During summer in the Northern Hemisphere, the time in
each day that it is light increases as you move towards the
North Pole
• Areas north of the Arctic Circle have 24 hours of daylight
called “midnight sun”
– At the same time, the Antarctic Circle has 24 hours of darkness
called “polar night”
– These conditions reverse with the seasons
WHAT CAUSES
SEASONS?
• Most locations on Earth experience seasons
• Each season is characterized by a pattern of temperature
and other weather trends
• Near the equator, the temperatures are almost the same
year-round
• Near the poles, there are very large changes in
temperatures from winter to summer
• We experience a change in seasons due to:
– the changes in the intensity of sunlight (angle of the Earth)
– the number of daylight hours
• As Earth travels around the sun the area of sunlight in each
hemisphere changes
• Equinox – sunlight shines equally on both hemispheres
– September and March
• Solstice – area of sunlight is at a maximum in one
hemisphere and at a minimum in one hemisphere
– December and June