Sunset

Sunset, also known as sundown, is when the Sun disappears below the horizon of the Earth because of the Earth's rotation. This beautiful event happens about once every 24 hours almost everywhere on our planet, except near the poles. During the equinox periods in spring and autumn, the Sun sets directly west.

In astronomy, sunset is the exact moment when the top edge of the Sun goes below the horizon. Because of something called atmospheric refraction, the Sun actually is already below the horizon when we see it disappear. This makes the Sun look slightly higher than it really is.

Sunset is different from twilight, the soft light we see after the Sun goes down. Twilight has three stages: civil twilight, nautical twilight, and astronomical twilight. After these stages come dusk, which is the darkest part just before night falls. When the Sun is 18 degrees below the horizon, it is finally night.

Occurrence

See also: Analemma

The time when the Sun sets changes throughout the year and depends on where you are on Earth. This is influenced by the Earth's tilt, its rotation, and its path around the Sun. In places far from the poles, the Sun sets about once every day. During winter and spring, days get longer and sunsets happen later each day. The latest sunset usually happens a little after the summer solstice, not exactly on the day of the solstice itself. This depends on where you live.

In the Southern Hemisphere, the pattern is reversed. The earliest sunsets happen before the winter solstice, and the latest sunsets occur after the summer solstice. Near the equator, the time of sunrise and sunset changes only a little through the year. The Sun sets almost directly west during the equinoxes. In places inside the Arctic and Antarctic Circles, there are times when the Sun does not rise or set for a whole day or more, called polar day and polar night. This happens because of the Earth's tilt.

Location on the horizon

Further information: Solar azimuth angle

The place where the sun disappears each evening changes depending on where you live and what time of year it is. Scientists can figure this out using special math that takes into account your location, the date, and the time of day. This helps us know exactly where in the sky the sun will go down.

Colors

Further information: Atmospheric optics

When sunlight shines through the Earth's air, some colors spread out more than others. Blue and green light spread out easily, so they often disappear before reaching our eyes. This is why during sunrise and sunset, we mostly see red and orange colors. The longer path of sunlight at these times helps remove the blue and green, leaving behind warm reds and oranges.

Sunset colors can sometimes look even brighter than sunrise because the evening air usually holds more particles. Rarely, just before sunrise or after sunset, a quick flash of green light can appear. Big events like volcanic eruptions can change sunset colors, sometimes making them even more colorful or softer depending on where the smoke and dust go in the sky.

Names of compass points

Some languages have special names for directions based on the Sun’s rising and setting. In English, the words "orient" (east) and "occident" (west) come from Latin words for sunrise and sunset. In Polish, the word for east, wschód, means "the Sun coming up", while the word for west, zachód, means "the Sun going behind". Similarly, in Russian, the word for west, запад, means "the Sun falling behind". In Hebrew, the word for east means "rising", and the word for west means "setting".

Historical view

See also: History of astronomy

In the 1500s, the astronomer Nicolaus Copernicus created a detailed model that showed the Earth moves around the Sun. Before this, many people thought the Sun moved around the Earth. Copernicus's idea was accepted by many and changed how we understand our world.

Planets

Sunsets on other planets look different because each planet is a different distance from the Sun and has different kinds of air around it.

The Moon

On the Moon, there is no air, so a sunset looks different from Earth. The change from light to dark happens more slowly because the Moon always faces Earth in the same way, and sometimes the Earth’s light can make the sky glow.

Mars

See also: Astronomy on Mars

On Mars, the Sun looks smaller than it does on Earth because Mars is farther from the Sun. The colors during sunset on Mars can be blue and last longer, looking much redder than on Earth. Mars has very little air and lots of red dust, which changes how the light looks.

Cultural significance

Sunsets are seen as beautiful by many people and are often used in paintings and photographs.

In some calendars like the Hebrew calendar, Islamic calendar, and Bahá'í calendar, as well as in Orthodox Christianity, the day begins at sunset.