Most of us think that sunset is when the sun dips below the horizon. That's true, but actually there are three types of sunsets, and knowing this is key to improving your landscape shots.
1. Civil Sunset: When the sun dips below the horizon (this is the one we all know about).
2. Nautical Sunset: When the first star appears in the sky (Venus).
3. Astronomical Sunset: When the last light fades out to complete darkness.
If you want the best landscape shots (those gorgeous pink and red skies), shoot after civil sunset, and before nautical sunset. If you want to shoot the night sky (astrophotography), shoot after astronomical sunset.