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Sunrise

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Sunrise is the specific moment when the upper rim of the Sun first appears on the horizon.

Spring Lake, New Jersey Beach at Sunrise
Spring Lake, New Jersey Beach at Sunrise

This event marks the beginning of the Sun's daily path across the sky. While it technically describes a single instant, people often use the term to describe the entire process of the solar disk crossing the horizon. This period is closely linked to twilight, which is the time when the sky brightens before the Sun is visible. The very first stage of this brightening is known as astronomical dawn.

Understanding sunrise requires looking at how light, the atmosphere, and planetary motion work together.

Although it looks like the Sun is rising, this motion is actually an illusion. The Sun remains relatively fixed while the Earth rotates on its axis. Because we are observing from a rotating reference frame, the Sun appears to move. For a long time, many cultures believed in the geocentric model, which placed Earth at the center of the universe. This changed in the 16th century when the astronomer Nicolaus Copernicus formulated the heliocentric model. This model correctly placed the Sun at the center of the system.

Sunrise-Sunset angle
Sunrise-Sunset angle

Architect Buckminster Fuller later suggested the terms "sunsight" and "sunclipse" to better reflect this heliocentric reality.

Measuring the exact moment of sunrise involves complex geometry and atmospheric physics. Astronomically, sunrise occurs when the upper limb of the Sun is tangent to the horizon. However, the atmosphere bends light through a process called refraction. At the horizon, the average amount of refraction is 34 arcminutes. This bending can create a "false sunrise," where the Sun appears above the horizon even though it is still below it.

False Sunrise
False Sunrise

Because the Sun is a disk rather than a single point, we measure from its upper limb. The apparent radius of the Sun at the horizon is 16 arcminutes. When you combine these factors, sunrise occurs when the Sun's center is 50 arcminutes below the horizon.

The timing of sunrise is never the same every day. It changes based on your latitude, longitude, altitude, and time zone. These variations are driven by the Earth's axial tilt and its elliptical orbit around the Sun. It is also affected by the paired revolutions of the Earth and the Moon. In temperate latitudes, sunrise occurs earlier each day during late winter and spring. It reaches its earliest time shortly before the summer solstice. After that, the time of sunrise gets later each day until the winter solstice.

Sunrise - Libreville, Gabon - 2008
Sunrise - Libreville, Gabon - 2008

Scientists use a tool called an analemma to help predict these shifting times.

Sunrise also changes depending on where you look on the horizon. In temperate regions, the Sun rises in the northeast quadrant from the March equinox to the September equinox. From the September equinox to the March equinox, it rises in the southeast quadrant. On the equinoxes themselves, the Sun rises approximately due east for everyone on Earth. The exact position, or azimuth, can be calculated using complex solar geometry routines. These calculations must account for the Sun's declination and the specific hour angle of the sunrise.

The brilliant colors of sunrise are caused by how light interacts with the atmosphere. As sunlight travels through the air, molecules and particles scatter the light. This involves two main processes: Rayleigh scattering and Mie scattering. Rayleigh scattering occurs when light hits molecules much smaller than its wavelength. This process removes blue and green light from the beam because those colors scatter more strongly.

2012-10-14 09-02-47 Portugal Lisboa Campolide
2012-10-14 09-02-47 Portugal Lisboa Campolide

This leaves the longer-wavelength orange and red hues to reach our eyes. Mie scattering happens when light hits larger particles, like cloud droplets, which is not strongly dependent on wavelength.

Other factors can make these colors even more dramatic. Volcanic eruptions can change the appearance of the sky by adding particles to the atmosphere. If ash stays in the troposphere, it can mute the colors. However, if volcanic ejecta reaches the stratosphere, it can create beautiful "pre-sunrise glows." For example, eruptions of Mount Pinatubo in 1991 and Krakatoa in 1883 produced remarkable afterglows. These high-altitude sulfuric acid droplets reflect reddened sunlight back down to the surface. These atmospheric connections show how even distant geological events can change our daily view of the sky.

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🖼️ Images & Media (8)
File:Spring Lake, New Jersey Beach at Sunrise.jpg
Spring Lake, New Jersey Beach at Sunrise.jpg
File:Wieże kościoła na Bielanach w Krakowie ponad Lasem Wolskim, 20201122 0729 5085.jpg
Wieże kościoła na Bielanach w Krakowie...
File:Sunrise-Sunset angle.svg
Sunrise-Sunset angle.svg
File:Sunrise - Libreville, Gabon - 2008.svg
Sunrise - Libreville, Gabon - 2008.svg
Twilight and Sunrise in Gjøvik in...
File:The sunrise of Jan 1st 2025.jpg
The sunrise of Jan 1st 2025.jpg
File:2012-10-14 09-02-47 Portugal Lisboa Campolide.JPG
2012-10-14 09-02-47 Portugal Lisboa Campolide.JPG
File:False Sunrise.jpg
False Sunrise.jpg
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