Astronomy
The Path of the Sun
• Have you ever noticed
how the sun moves across
the sky during the course
of a day?
• Does the sun change its
path through the sky from
month to month?
• Are there certain times
when you know through
which part of the sky the
sun will travel?
• These questions are
best answered if you
have an entire year to
make observations of
the Sun to see how its
movement through the
sky varies.
• Since we do not have an entire year to
observe the Sun, lets take a look at a few
key terms and concepts that may help you
understand the Sun's motion. . .
The Path of the Sun
• An arc is the apparent
path the sun takes
across the sky.
• The sun appears to
move across the sky
(arc) from east to west
because Earth rotates
on its axis.
• Hemispheres are equal divisions of the Earth.
• The Earth is divided into four hemispheres:
– North, south, east and west.
• Local Solar Noon is the
time when the sun is at its
highest point of the day;
does not necessarily have
to occur at 12:00 o’clock,
noon.
• The sun only reaches an
altitude of 90º in the
tropics! In NYS it only
reaches a maximum
altitude of ~ 73°, and
even that’s only for a day!
• The point in the sky
located directly above
an observer is called
the Zenith.
• An observer’s zenith is
always 90 degrees.
• Azimuth is the
direction of an object
measured clockwise
around an observer
along the horizon.
–
–
–
–
–
North = 0º
East = 90º
South = 180º
West = 270º
Back to North 360º
• The angle of an object
above the horizon is
its altitude.
• An object’s altitude
can range from 0º to
90º.
– 0º = horizon
– 90º = zenith
Altitude and azimuth are always used together . . .
• Altitude
– Angle UP 
• and
• Azimuth
– Angle AROUND
Does the Sun ‘Rise in the east and set in
the west’ ? Sort of . . .
• Many people know that the Sun rises in the east and sets in the west,
but does NOT rise EXACTLY east and set EXACTLY west every day?
• We also know that the days are longer in the summer and shorter in the
winter, but have you ever thought about how the Sun's path through the
sky is changing to create these differences?
• The path of the sun changes over the course of the year because of
Earth’s TILT and REVOLUTION.
• We’re facing the sun in the summer, so it appears in the sky longer.
We’re facing away from the sun in the winter, so it is in the sky for a
much shorter period of time.
• Thus, between the summer solstice and the winter solstice the sun
moves in a changing arc across the sky; it covers 242 degrees of
azimuth in the summer and only 114 degrees of azimuth in the winter
~ less than half of the summer arc!
Summer Solstice
• On June 21st, the Sun is at its highest declination (altitude),
(+23.5 degrees from the altitude at equinox; 71.5 degrees).
• The path of the Sun on that day is longest, so the length of the
daylight hours is longest.
• It rises NORTH of East and sets NORTH of West.
Equinox
•
•
•
•
•
Equi = Equal / Nox = night
Equinox means equal night (and equal day!)
12 hours of day and 12 hours of night everywhere on the globe.
Occurs around March 21 (Spring) and September 21 (Fall)
At our location in New York, the sun’s altitude on the equinox is
48 degrees.
• The sun rises exactly east (90°E) and sets exactly west (270°W)
Winter Solstice
• On Dec 21st, the Sun is at its lowest declination, (-23.5
degrees from our altitude at the equinox; 24.5 degrees).
• The path of the Sun on that day is shortest, so the length of
the daylight hours is shortest.
• The sun rises SOUTH of east and sets SOUTH of west.
Only the shadow knows . . .
• Ever notice how the
length of your shadow
changes throughout
the day, depending on
what time you’re
outside?
• It changes with the
seasons, too!
• Shadow length is determined by the altitude of the sun.
• The higher the sun is in the sky, the shorter the shadow
(inverse relationship).
• i.e. ~ longer shadows in the morning and evening, shorter
shadows at noon; longer shadows in the winter, shorter
shadows in the summer.
Final summary;
• The sun follows an arc
across the sky due to
Earth’s rotation on its
axis.
• The sun’s azimuth is a
result of our rotation.
• We experience seasons as
a result of Earth’s tilt;
toward the sun in summer
and away from the sun in
winter as we revolve
around it.
Summary (continuted …)
• The altitude of the sun
depends on where we are
in our revolution. The sun
follows the same basic
path across the sky each
day; but it travels in a long
arc from NE to NW in the
summer, reaching a higher
altitude; and a short arc
from SE to SW in the
winter, reaching a lower
altitude. The only time it
rises and sets exactly east
and west is on the
equinox.
In a nutshell . . .
•http://solar.physics.montana.edu/YPOP/Classroom/Lessons/Sundials/sunpath.html