Comet C/2023 A3 (Tsuchinshan–ATLAS) at Dawn over Mauna Kea, Hawaii
Comet C/2023 A3 (Tsuchinshan–ATLAS) at dawn over Mauna Kea. The zodiacal light is seen to the left. Mauna Kea is a dormant shield volcano on the island of Hawaiʻi. Its peak is 4,207.3 m (13,803 ft) above sea level, making it the highest point in Hawaii.
C/2023 A3 (Tsuchinshan–ATLAS) is a comet from the solar system's Oort cloud discovered by the Purple Mountain Observatory east of Nanjing, China, on January 9, 2023, and independently found by the automated Asteroid Terrestrial-impact Last Alert System (ATLAS) in South Africa on February 22, 2023. ATLAS is funded by NASA's planetary defense office, and developed and operated by the University of Hawaii's Institute for Astronomy. C/2023 A3 passed perihelion (closest approach to the Sun) at a distance of 0.39 AU (58 million km; 36 million miles) on September 27, 2024.
The Oort cloud is theorized to be a vast cloud of icy planetesimals surrounding the Sun at distances ranging from 2,000 to 200,000 AU (0.03 to 3.2 light-years). The concept of such a cloud was proposed in 1950 by the Dutch astronomer Jan Oort, in whose honor the idea was named. Oort proposed that the bodies in this cloud replenish and keep constant the number of long-period comets entering the inner Solar System—where they are eventually consumed and destroyed during close approaches to the Sun.
The zodiacal light—also called “false dawn” when seen before sunrise—is a faint, diffuse band of light in the night sky, reaching up from the horizon. It follows the direction of the ecliptic—the plane of Earth's orbit around the Sun. This plane is rich in tiny particles of dust. It scatters sunlight and creates this phenomenon.
Credit: International Gemini Observatory / NOIRLab / NSF / AURA/ M. Rodriguez
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