alt text
Credit: E. Wiebe

Sunrise seen from Glencoe Cove Park in Saanich, British Columbia. The view is approximately to the southeast and the peaks are coastal mountains in Washington State, USA.

The Earth is a rotating sphere covered in an atmosphere. While the sun is below the horizon rays travel a long path through the air (and whatever matter is suspended in the air, water droplets or ice crystals, dust, smoke, etc.).

It turns out that clean air is rather good at scattering the shorter wavelengths of light (the bluer colours) from the beam of light directly from the sun. That light then appears to radiate from the atmosphere itself, making the clear sky appear blue.

For longer path lengths and especially when there the air is a bit dirty more and more long wavelength light gets scattered out as well. What's left is the red glow of a beautiful crepuscular sky. As you scan upward in the sky away from the horizon you see progressively shorter wavelengths of visible light.

Whispy cirrus clouds in this scene are still mostly unlit by direct light from the sun so appear dark against the brighter sky.

In this picture you can also see a mirage. This is an inferior mirage and what you see is an upside down image of the sky lying over the water. This is caused by a warm layer of air under a colder atmosphere. In this case the (relatively) warmer water of Strait of Juan de Fuca is keeping the lowest layer of the atmosphere warm as well.

UVic / SEOS / Climate Group / About Front Page Picture / Sunrise from Saanich, BC Last updated: Monday, 02-Dec-2013 13:31:03 PST
You are free to use images on this page for non-commercial purposes under this license and as long as proper credit is given.