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Reasons
for Seasons
Exploring the Astronomy of Spring
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SEASONAL
Cycles vs. DAILY Cycles
Why
do some sun cycle events occur at one single moment for all places on
earth, while other sun cycle events occur at different times based on
the observer's location?
The
answer lies in the difference between seasonal sun cycle
events and daily sun cycle events.
- Moments
or events in seasonal cycles (e.g., spring and fall equinox,
summer and winter solstice) occur everywhere on Earth at the same time.
The timing of such seasonal events relates to the Earth's location in
space as it revolves around the sun (and not to when something happens
locally on Earth). The time of an equinox is an example of this. Specifically,
the equinox is defined by the moment when the Sun passes over the plane
of Earth's equator. Therefore, an equinox happens at one single
moment in space and time, which is not related to something happening
locally at your location.
It's
All About Time Zones: "When" a seasonal cycle event happens
depends on where you are because different locations usually use different
local time zones. For example, when the equinox occurs, if you're
standing at Greenwich and you look at your watch you would see it
is 1:00 a.m. on March 21. But if I'm standing in New York when the
same equinox occurs, my watch reads 9:00 p.m. on March 20. It's the
same event at the same moment, but the time and date are different
due to local timekeeping.
- Moments
or events in daily cycles (e.g., sunrise, noon, sunset) occur
at different moments in different local places on Earth. The timing
of such daily events relates to Earth's spinning (rotating) on its axis.
For example, sunrise happens at different times in different locations,
because each sunrise relates to when something happens in a specific
local location, namely when the sun's light can be seen in that location.
Because the Earth rotates each day, the sun hits different areas at
different times. Everybody is NOT on the same place on Earth!
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