A sunset is a beautiful natural phenomenon that occurs when the sun disappears below the western horizon. It is defined by the combination of optical effects that occur as the sun’s light passes through Earth’s atmosphere near the horizon. There are many factors that affect the stunning colors, visibility, and duration of a sunset.
When and where do sunsets occur?
Sunsets occur daily when the sun reaches the horizon in the western part of the sky. The specific timing of sunset depends on your location on Earth as well as the time of year.
Locations closer to the equator experience earlier sunsets and shorter twilight durations than locations farther from the equator. This is due to the tilt of Earth’s axis of rotation relative to its orbit around the sun.
| Latitude | Sunset Time | Twilight Duration |
|---|---|---|
| 0° (equator) | Around 6 pm year-round | 30-45 minutes |
| 40° north (e.g. Philadelphia, USA) | Between 4:30 and 8 pm depending on season | 1-1.5 hours |
| 60° north (e.g. Helsinki, Finland) | Between 3 and 10 pm depending on season | 2-3 hours |
The further north or south of the equator, the more sunset times and twilight duration vary throughout the year.
Optical effects that define sunsets
There are several optical atmospheric effects that occur at sunset to create the vivid colors and darkening sky:
- Rayleigh scattering – scattering of shorter wavelength blue and violet light by air molecules causes the sky to appear blue in the day. As the sun sets, its rays pass through more atmosphere near the horizon, leading to more scattering of shorter wavelengths. This leaves more long wavelength red and orange light to reach our eyes, causing the vivid orange and red hues of sunset.
- Mie scattering – scattering of light by aerosols and particulate matter in the atmosphere. This spreads out and diffuses sunlight, causing the enlarged size of the setting sun and its red/orange color.
- Light absorption – the lower atmosphere absorbs more red light as the sun sets lower on the horizon, shifting sunset colors from orange to a darker red.
- Extinction – the combined effects of scattering and absorption of light attenuate or ‘extinguish’ sunlight passing through the atmosphere. This causes the dimming of the sky and landscape as the sun sets.
The interplay between these optical phenomena defines the changing colors and darkening skies as the sun disappears below the horizon at sunset.
Factors that affect sunset colors
Many factors can affect the vividness and hues present in a sunset sky:
- Aerosols – More dust, smoke, pollution, or other aerosols in the atmosphere lead to more vivid and colorful sunsets due to increased scattering of light.
- Cloud cover – Clouds near the horizon can act like a reflective screen to display stunning sunset colors. However, thick cloud cover can block sunset views.
- Humidity – Higher humidity increases the refraction of sunlight, spreading it out for a more vibrant, elongated sunset.
- Location – Proximity to the equator and longitude affects sunset timing and colors due to the solar angle.
- Season – The solar angle varies throughout the year, leading to longer summer sunsets with deeper red hues.
- Weather – Clean, stable air allows more vivid sunsets than storms or windy conditions which can obscure and distort the sunset.
Under optimal atmospheric conditions, these factors can combine to create a breathtaking sunset viewed by observers around the world.
Green flash sunsets
A rare and stunning phenomenon called a “green flash” can sometimes occur right at sunset under just the right conditions. A green spot or green flash above the sunset point lasts just a few seconds, caused by light refraction in the atmosphere.
For a green flash to occur, these ideal conditions are needed:
- Very clear and cloudless sky near the horizon
- A turbulent, mirage-producing atmosphere
- An unobstructed view of the horizon
- No haze or pollution near the horizon
The frequency and likelihood of observing a green flash depends greatly on the observer’s latitude. Locations near the equator offer more opportunities per year for green flash sunsets.
| Latitude | Green Flash Frequency |
|---|---|
| 0-10° (tropics) | Up to 400 times per year |
| 20-30° (subtropics) | ~100 times per year |
| > 30° (mid-latitudes) | ~20 times per year |
Catching a green flash sunset is a magical, fleeting moment for skywatchers lucky enough to witness one.
Twilight phases after sunset
Sunset also kicks off the different phases of twilight that occur as the sun continues disappearing below the horizon:
- Civil twilight – Brightest phase, starting at sunset and lasting when the sun is 6° below the horizon. Outdoor activities can generally be done without artificial lighting.
- Nautical twilight – The sun is between 6° and 12° below the horizon. Low natural light, making navigation challenging at sea.
- Astronomical twilight – Darkest phase, when the sun is between 12° and 18° below the horizon. Often the best conditions for stargazing before night sets in.
The duration of twilight depends on time of year and latitude – lasting shorter closer to the equator, and longer farther from it. The various phases of twilight provide ever-changing conditions for skywatching after sunset fades away.
Symbolism and cultural significance
In many cultures around the world, sunset carries important symbolism, spirituality, and meaning:
- Marking the transition from day to night
- Representing the cycle of life and passage of time
- Associated with conclusion, closure, retirement, or old age
- Inspiring introspection, reflection, and meditation
- Symbol of passion, desire, romance, warmth in relationships
- Motif for the beauty and impermanence of life
Sunset is a prominent theme across literature, poetry, art, music, and film worldwide. Its vivid imagery and symbolism will likely continue inspiring cultural expression across the ages.
Photographing stunning sunsets
Capturing brilliant photos of sunsets takes skill, timing, and these helpful photography tips:
- Use a tripod for sharp, well-composed shots
- Shoot in RAW format to allow post-processing adjustments
- Use high ISO and wider aperture to compensate for low light
- Frame with interesting foreground objects like trees, buildings, or water
- Shoot sequences to capture fading light over time
- Bracket exposure for high-dynamic range images
- Include people, structures, or objects to add scale and perspective
Planning sunset photo shoots around ideal weather conditions and interesting locations can result in breathtaking images to share.
Conclusion
Sunset is a beautiful and inspiring daily phenomenon that reveals the complex optical effects of sunlight interacting with Earth’s atmosphere. The timing, colors, visibility, and experience of sunset vary greatly based on location and environmental conditions. Sunsets hold deep cultural meaning and appeal worldwide. Their stunning beauty and vibrant colors never cease to amaze observers lucky enough to catch them. Though its duration is fleeting, a gorgeous sunset has the power to lift the human spirit and remind us of nature’s grandest displays.
