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IQ Weather Blog: Summer Twilight

Now that we have passed the mid-point of summer, and heading rapidly toward meteorological fall on September 1st, the daylight is starting to become noticeably shorter across the United States.

As of today, August 2nd, the amount of daylight loss ranges from about 1 minute in south Florida, to about 30 minutes in northern Alaska!

We talk a lot about the sun’s impact on weather, and the longer daylight hours during the summer months make it easier for the atmosphere to stay warm and heat up quickly each day.

But, as the daylight begins to shorten and the sun angle lowers, it allows the heat of the summer to begin to back off slowly.

The oceans store enormous amounts of heat, and because they release that heat slowly, there is a lag time between the longest days and the hottest days of summer. That is why the weather stays relatively warm even into the autumn months.

What we love here at IQ Weather is how the summer evenings can remain so bright even after the sun has dropped below the horizon. That also has a lot to do with the sun angle.  The light remaining in the sky after the sun has set, is called twilight.  But do you know there are several types of twilight? They are civil, nautical, and astronomical twilight.

Civil twilight is the brightest form of twilight. There is enough natural sunlight during this period that artificial light may not be required to carry out outdoor activities. Only the brightest celestial objects can be observed by the naked eye during this time.

Nautical twilight less bright than civil twilight and artificial light is generally required for outdoor activities. The term, nautical twilight, dates back to the time when sailors used the stars to navigate the seas. During this time, most stars can be easily seen with naked eyes, and the horizon is usually also visible in clear weather conditions.

During astronomical twilight, most celestial objects can be observed in the sky. However, the atmosphere still scatters and refracts a small amount of sunlight, and that may make it difficult for astronomers to view the faintest objects.

This graph shows a depiction of the sun angle for each type of twilight:

For a more detailed description of twilight phases, click here!

Homeschool science, online weather course, astronomical twilight, civil twilight, nautical twilight, solar science, sun angles



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