Sunrise and sunset
The Sun is seen a little early and a little late.
Before the Sun is really up
The actual sunrise is the moment the Sun crosses the horizon. But the air above the earth bends sunlight.
When do you first see the Sun?
What this lesson covers
The idea
Because of atmospheric refraction, the Sun is visible about 2 minutes before actual sunrise and about 2 minutes after actual sunset, and its disc appears flattened at sunrise and sunset.
Before the Sun is really up
The actual sunrise is the moment the Sun crosses the horizon. But the air above the earth bends sunlight.
When do you first see the Sun?
- About 2 minutes before the actual sunrise
- Exactly at the actual sunrise
- About 2 minutes after the actual sunrise
Light through the atmosphere
Press Next step. The picture is only an illustration: the bending is exaggerated.
Early and late
Because of atmospheric refraction, the Sun is visible about 2 minutes before the actual sunrise and about 2 minutes after the actual sunset. By actual sunrise we mean the actual crossing of the horizon by the Sun. The same phenomenon makes the Sun's disc look flattened at sunrise and sunset.
Atmospheric refraction makes the Sun visible about 2 minutes before the actual sunrise and about 2 minutes after the actual sunset, and makes its disc look flattened at sunrise and sunset.
Notes
Because of atmospheric refraction the Sun is seen about 2 minutes before the actual sunrise and about 2 minutes after the actual sunset, and its disc looks flattened.
Check yourself
By about how many minutes is the Sun seen before the actual sunrise? (minutes)
Answer: 2
About 2 minutes before the actual sunrise.
By about how many minutes is the Sun seen after the actual sunset? (minutes)
Answer: 2
About 2 minutes after the actual sunset.
By the actual sunrise we mean…
The Sun's disc looks flattened at sunrise and sunset because of…
- the moment the Sun first becomes visible to us. By actual sunrise, we mean the actual crossing of the horizon by the Sun.
- the moment the sky turns bright. By actual sunrise, we mean the actual crossing of the horizon by the Sun.
- the actual crossing of the horizon by the Sun — correct. Yes!
- atmospheric refraction — correct. Yes!
- scattering of blue light. The apparent flattening of the Sun's disc at sunrise and sunset is due to atmospheric refraction.
- the Sun really changing shape. The apparent flattening is due to atmospheric refraction.