Sunrise signifies the initial ascent of the sun above the horizon, marking the beginning of a new day. It typically denotes the moment when the sun gradually emerges from the eastern horizon, illuminating the sky with its radiant glow.

More precisely, sunrise refers to the instant when the sun's surface first appears above the horizon, rather than when the entire sun's disk clears the horizon completely.

The Earth rotates every day, completing a full rotation once in 24 hours. When people are on the side of the Earth facing away from the sun, it is nighttime. As the Earth continues to rotate, people will eventually reach the position where they can see the sun, marking the beginning of a new day and the sunrise. This cycle repeats, allowing people to witness the sunset and sunrise on a daily basis.

The time of sunrise will vary with the seasons and the latitude of each place. Traditionally, it is believed that in the northern hemisphere, the sun rises the latest during the winter solstice, but in fact, the latest sunrise should be in early January. By the same token, the earliest time for sunrise is not at the summer solstice, but at the beginning of June. Even at the equator, the times of sunrise and sunset vary slightly throughout the year.

The solar spectrum is a continuous spectrum of different wavelengths, which can be divided into two parts: visible light and invisible light. Visible light has a wavelength of 400-760 nm. After scattering, it is divided into red, orange, yellow, green, blue, indigo, and violet. The seven different colors of light vary in their ability to penetrate the atmosphere. Red light has the greatest ability to penetrate the atmosphere, followed by orange light.

The sunrise unfolds in a mesmerizing sequence of colors and light. As the sun prepares to emerge, a faint band of white appears on the horizon, gradually transforming into hues of soft pink or orange. As the clouds gently disperse, a vivid red line emerges on the horizon, heralding the imminent arrival of the sun. Initially, the sun's halo becomes visible, casting a radiant glow across the sky. Then, with gradual ascent, the sun rises, casting a warm red hue that illuminates the adjacent clouds with vibrant shades of orange.

During the early morning and evening, sunlight passes through the atmosphere at an oblique angle. Due to the thickness of the atmosphere, only the most penetrating red and some orange light can make it all the way through. Other colors of light are reflected by the atmosphere and are unable to reach us. Therefore, during sunrise and sunset, the sun appears to be extra red.