Daylight cycle

The day/night cycle is a 20 minute long lapse between two main light settings.

Daytime
Daytime is the longest section of the cycle, lasting 10 minutes.
 * When a player first spawns in Infdev, Alpha, and Beta the cycle will always start right at the beginning of daytime.
 * Daytime features the Sun, and a light blue sky.
 * During daytime, all blocks that are in direct vertical view of the sky receive daylight, the strongest light possible, which is light level 15.
 * Daylight provides ample light for the growth of all trees and crops.
 * Zombies and Skeletons in direct view of the sky (and not in water or ice) during daytime will be set on fire.

Sunset
Lasts 1 ½ minutes.
 * A period between daytime and nighttime, when the Sun sets on the West horizon, and the Moon rises on the East horizon.
 * All blocks that are in direct vertical view of the sky get 1 shade of lighting darker every 10 seconds.
 * The sky near the setting sun will have a red glow when the sun sets.
 * Actual time of Sunset will not change if the texture for the sun is changed. The day/night cycle will be the same length with the same effects even if the sun is visibly larger or smaller.
 * The sun will also get visibly larger when it sets.

Nighttime
Lasts 7 minutes.
 * During nighttime the world is covered in darkness with a light level of 4, and hostile mobs may spawn on the surface.
 * Nighttime features the Moon, and a dark black sky, with white stars.

Sunrise
Lasts 1 ½ minutes.
 * A period between nighttime and daytime, when Moon sets on the West horizon, and the Sun rises on the East horizon.
 * All blocks that are in direct vertical view of the sky get 1 shade of lighting brighter every 10 seconds.
 * The sky near the rising sun will have a red glow when the sun rises.
 * The sun will slowly shrink to its 8x8 pixel size while rising.

Clock
In the Halloween Update, Notch added a clock that lets you tell the time in the "Minecraft" world. It's crafted like this:



Note: The clock will not work in the Nether, due to the fact that the Nether does not receive Day or Night.

Trivia

 * In the Minecraft sky, the Sun and Moon always appear in the same position relative to the stars.
 * When looking directly at a star that is uncovered by a cloud, it will appear over the cross-hair.
 * Due to a bug, some chunks don't change light level due to the day/night cycle. this is a rare bug, but it seems most commom in the Taiga biome.

Time Measurements
The Approximation Of Minecraft Time to Real Time


 * 1 Minecraft Year is ≈ 120 Hours of gameplay. ( 10 + 7 + 1.5 + 1.5 ) * 365 / 60 = 120
 * 1 Minecraft Month is ≈ 10 Hours of gameplay. ( 10 + 7 + 1.5 + 1.5 ) * 30 / 60 = 10
 * 1 Minecraft Week is ≈ 2.333 Hours of gameplay. ( 10 + 7 +  1.5 + 1.5 ) * 7 / 60 = 2.333
 * 1 Minecraft Day is = 20 Minutes of gameplay. 10 + 7 + ( 1.5 + 1.5 ) = 20

The Approximation Of Real Time to Minecraft Time


 * 1 Real Day of gameplay is = 72 Minecraft Days. 24 * 60 / 20 = 72

''Note: Real time is the time spent playing minecraft.