Sunny but cold - Seasons - Science Project answers questions


Skiing on a sunny day
Still in their coats on a sunny day
(Thanks to [seattle + beyond])

To see what a difference it makes whether sunlight hits the Earth directly or at an angle, just think about a sunny day in summer and a sunny day in winter. In summer, when the sun is out it soon gets very hot. Even cloudy days, when the sunlight has to come through clouds, are often very hot. But in the wintertime, even when the sun is out all day, it's still cold. That's because instead of being right overhead, the sun stays lower in the sky all day, and the sunlight hits the ground at an angle.

When the sunlight hits the ground at an angle, the same amount of light - the same number of photons - have to cover much more ground than before, so there are fewer photons for each bit of ground. To see this for yourself, take a flashlight outside at night and point it straight at the ground so that it makes a circle of light. Now slowly tilt the flashlight, so that your circle of light becomes an oval. Is the light dimmer in the oval than it was in the circle? Try tracing your circle and your oval and calculating the area of the circle and the area of the oval. Which one is bigger?

First project to explain the seasons
More about the Earth
More about Weather
More about Seasons

Bibliography and further reading about the seasons:

Physics home

Professor Carr

Karen Eva Carr, PhD.
Assoc. Professor Emerita, History
Portland State University

Professor Carr holds a B.A. with high honors from Cornell University in classics and archaeology, and her M.A. and PhD. from the University of Michigan in Classical Art and Archaeology. She has excavated in Scotland, Cyprus, Greece, Israel, and Tunisia, and she has been teaching history to university students for a very long time.

Professor Carr's PSU page

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