Monday, August 31, 2015

Forest Fires, Smoke, and Transparency

Forest fires are raging in the northwestern U.S. and western Canada, taking lives and resulting in the destruction of property. There are a lot of fires:

Active fires on 8/31/15. Map from

The effects are not limited to the areas of burning. Smoke is being carried hundreds of miles eastward, leading to occasional serious decreases in air quality that can affect those with respiratory illness.

Another far less serious effect is the greatly diminished transparency of the sky. During the day the sky is a yellow-brown veil and at night dimmer stars are extinguished and the moon starts to look like it's in eclipse:

The full moon at an altitude of 34 degrees. It should be colorless, not yellow!
Most observing and imaging activities are put on hold until either the fires end or the winds shift. This degree of transparency loss has happened before, earlier this year and once last year. Prior to that I think one must go back about seven years or so to see a similar event.

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