Sunrise and sunset in Santa Lucía, San Juan, Argentina

Each twilight begins at the morning time and ends at the evening one.

• Longest day: December 21, 14 h 13 min, from sunrise at 06:25 to sunset at 20:38.
• Shortest day: June 21, 10 h 05 min, from sunrise at 08:33 to sunset at 18:38.

• Sunrise and sunset mark the moment the Sun’s upper edge touches a level horizon, with the air’s usual bending of light allowed for. Hills, buildings and altitude move what you see by a few minutes.
• Civil, nautical and astronomical twilight end when the Sun is 6°, 12° and 18° below the horizon. Golden hour here is the photographers’ usual definition: the Sun less than 6° above it.
• Worked out when the page loads from NOAA’s solar equations, for 31.5° S, 68.5° W, and accurate to about a minute.

How the layers work, where their data comes from and what they can’t tell you: Day and night, live, The Sun, Moon and planets