Earth orbits the Sun once every year. In
other words, the Earth’s path through space is a (roughly)
circular path. It takes about 365.25 days for the Earth to
complete one orbit around the Sun.
Earth spins on its axis once every 24 hours. This is what
causes day and night because as your location spins from sunrise
to sunset and back to sunrise again you go from Earth’s
shadow to the sunlit side of the Earth, back into the shadow and
around again into the light. This axis of rotation is tilted
relative to Earth’ orbit around the Sun. The tilt of the
Earth’s axis is 23.5° from perfectly vertical. That is,
the axis tilts 23.5° down from the direction that is at
90° to the orbit of the Earth around the Sun.
Earth’s axis currently points at a point in the heavens
very near to the star Polaris. That is why Polaris is called the
North Star or Pole Star. No matter where the Earth is in its
orbit around the Sun its axis always points toward Polaris. The
relationship between the direction that the axis points and the
direction of the Sun determines the seasons. It is Summer in the
Northern Hemisphere (North of the equator) when the North Pole is
pointing right at the Sun. It is Winter when the North Pole is
pointing directly away from the Sun. Spring and Autumn begin when
the axis of the Earth is at right angles to the direction of the
The seasons in the Southern Hemisphere of the Earth (South of
the equator) are the opposite of the seasons in the Northern
Hemisphere. For example, when it is Summer here in Maine it is
Winter in Australia. When it is Autumn in England it is Spring it
There are four special dates during the year that are
considered the first day of each season in the Northern
21st Vernal Equinox
1st Day of Spring
21st Summer Solstice
1st Day of Summer
21st Autumnal Equinox
1st Day of Autumn
December 21st Winter Solstice
1st Day of Winter
Answer the following questions based on your class notes and
the information above. Use complete sentences in your answers:
you will need to use more than one sentence in some cases.
Using the dates for each of the Equinoxes and Solstices
(given above) figure out what fraction of the year passes between
the beginning of each of the seasons. Draw a picture of the orbit
of the Earth around the Sun. You may draw it as if from above and
show the orbit as a circle with the Sun in the middle. Draw the
Earth on its orbit four times, once for each of the special
Use the pictures below to draw in the Earth’s Axis and
shadow for each of the special dates. Call the location on the
bottom of each picture the Vernal Equinox. Label the other
positions appropriately. The location of Polaris is above the
paper and to your left as you look at the paper flat on the desk. Make sure the axis always points at
There are four pictures below. 1
Label each of the four in order starting with the Vernal Equinox.
2 On each picture draw a line showing
the orbit of the Earth. 3 Draw the
Earth’s axis relative to the Sun. The North Pole should be toward the top of the page. In these pictures the
axis will not always point in the same direction:
sometimes the axis is parallel to the Earth’s orbit
sometime perpendicular and sometimes in between.
4 Finally, shade the side of the
Earth that is in shadow due to the illumination of the Sun.
Pick a point on the surface of the Earth in the Northern
Hemisphere and mark it on each of the pictures above. To answer
the following questions imagine what Day and Night would be like
for a person standing in the spot you picked. Remember that as
the Earth turns on its axis the spot you mark will move
perpendicular to the axis that you drew. Check with your teacher
to be sure that you have the axis drawn correctly for each
picture. Or look it up online.
A day is 24 hours long. Approximately
what fraction of the 24 hours is the spot you picked in sunlight
on the Vernal Equinox? So how long is the night by
Is the day longer than the night or vice
versa on the Summer Solstice for someone in the Northern
What can you say about the relative
length of day and night on the Autumnal Equinox?
Is the day longer than the night or vice
versa on the Winter Solstice for someone in the Northern
The word Equinox comes from Latin and
means ‘equal night’. Explain why this is appropriate
for the Vernal and Autumnal Equinoxes.
What is the longest day in the Northern
Hemisphere? What is the longest day in the Southern Hemisphere?
Why is it different?
Why are the seasons in the Southern
Hemisphere the opposite of the seasons in the Northern
Why do you think it is hot in the Summer
and cold in the Winter?
Earth is 3% closer to the Sun in January
than in July. Does Earth’s distance from the Sun have
anything to do with what causes the seasons?
What hemisphere did the people live in who decided on the
names of the four special dates (Vernal Equinox, etc.)? How do