The interstellar comet 3I/ATLAS will make its closest approach to Earth early Friday, December 19, offering a unique chance for astronomers and skywatchers to observe a visitor from beyond our solar system. This rare cosmic event marks the third confirmed interstellar object known to pass through our celestial neighborhood. The comet will come within approximately 168 million miles (270 million kilometers) of Earth, which is roughly twice the distance between our planet and the Sun.^{[1][2][3][4][5][6]} Its closest point will be at 1 a.m. EST (0600 GMT) on December 19.^[6] ### A Rare Visitor from Beyond Our Sun Comet 3I/ATLAS was first spotted on July 1, 2025, by the NASA-funded ATLAS (Asteroid Terrestrial-impact Last Alert System) telescope in Chile.^[1][7][3][6] The "3I" in its name signifies it as the third confirmed interstellar object ever recorded, following 1I/ʻOumuamua in 2017 and 2I/Borisov in 2019. ^{[1][8][9][3][5][6]}Scientists have determined that 3I/ATLAS originated from interstellar space, likely traveling for billions of years from the direction of the constellation Sagittarius, near the Milky Way's Galactic Center. ^[8][5] The comet is moving at an estimated speed of 130,000 miles per hour, making it the fastest interstellar visitor ever recorded. ^[1]Its trajectory is hyperbolic, meaning it will not orbit our Sun but will continue its journey back into interstellar space, never to return. ^{[8][7][3][4][10]}This unique path makes its current passage a fleeting opportunity for scientific study. The comet poses no threat to Earth as it passes safely by. ^{[2][8][7][3][6]} ### What to Expect in the Sky While 3I/ATLAS will not be visible to the naked eye, skywatchers can catch a glimpse using powerful binoculars or a backyard telescope. ^[1][6]The best viewing opportunity will be in the predawn sky, looking towards the east to northeast. ^[1]It should appear as a glowing star beneath Regulus, the brightest star in the constellation Leo. ^[1] For those unable to observe it directly, the Virtual Telescope Project will host a free online livestream of the comet's closest approach. ^[1][6][11]The webcast is scheduled to begin at 11 p.m. Eastern Standard Time on Thursday, December 18 (04:00 GMT on December 19), weather permitting. ^[1][6]Recent images captured by the Gemini North telescope in Hawaii show that the comet has developed a faint green glow. ^[2][10][12]This color change is due to different chemicals evaporating from its coma as the comet heats up from the Sun's radiation. ^[10][12] ### Unlocking Secrets of Other Star Systems The flyby of 3I/ATLAS offers scientists an invaluable chance to study material from another star system. This provides rare insights into how comets and planetary building blocks form around stars beyond our own. ^[3][5][6]"This could be your best bet to see this interstellar interloper," said Chelsea Gohd, a science writer at NASA's Jet Propulsion Laboratory. ^[1] Various space agencies and observatories, including the Hubble Space Telescope and ESA's Mars missions, have been closely tracking 3I/ATLAS. ^{[7][9][3][10]}Observations have revealed the comet is active, consisting of a solid icy nucleus surrounded by a coma, a cloud of gas and dust. ^[8]Researchers have detected unusually early outgassing of carbon dioxide, hydrogen cyanide, and methanol. ^[4]Scientists also found high amounts of nickel and iron in its composition, which is unusual for comets. ^[4][10] Darryl Z. Seligman, an assistant professor of physics and astronomy at Michigan State University, noted the significance of this event. "It has since been careening through the interstellar medium of the Milky Way galaxy for billions of years," Seligman said in an op-ed. "And we get front-row seats to watch as it gets close to our sun, for what is almost surely the first time it has ever gotten close to a star." ^[5]Studying these unique materials helps astronomers understand the diversity of planetary systems in the universe. This close pass of Comet 3I/ATLAS provides a critical, albeit brief, opportunity for humanity to examine a piece of another star system before it departs our solar system for good.

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