By Lauren Casey

PHILADELPHIA (CBS) — The smoke from wildfires out west is actually what is causing hazy conditions in the Philadelphia area Tuesday. A Code Orange is in effect.

That means it is unhealthy for certain groups of people to be outside — children, the elderly, and people with heart and lung conditions.

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On the flip side, the haze can result in an atmospheric feast for the eyes. Perhaps you witnessed the fiery red sunset Monday night? If not, get your camera ready as you’ll get another shot this evening.

Smoke from wildfires burning in western Canada thousands of miles away has infiltrated our atmosphere, carried on the powerful winds of the jetstream, to yield very hazy skies across the Delaware Valley.

But just how does the smoke create such vivid sunsets? It’s a combination of physics and our perspective.

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Smoke is a collection of tiny particles of mostly soot, tar, and ash, suspended in the air.

These smoke particles scatter the wavelengths of visible light emitted by the sun.

But the smoke plays favorites. It likes to scatter the shorter wavelengths of yellow, green, blue and violet. This is called preferential, or Rayleigh, scattering.

The longer wavelengths of red and orange are left to pass directly to the smoke layer and because at sunset the visible light has farther to travel to make it to our eyes, it spends more time in that smoke layer, thereby enhancing bright red spectacular sunset.

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Be sure to look for the sunset at 8:24 p.m.