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A Rare Visit from Green Comet 50,000 Years Ago Passes Solar System


February 6, 2023

A comet which last passed by our Solar System during the time of the ice age 50,000 years ago is now passing by us this January-February in a rare visit.  After this month, comet C2022 E3 (ZTF) may never be seen again.   It is considered a long-period comet from the Oort Cloud discovered by the Zwicky Transient Facility on March 2, 2022, thus designated with ZTF.  The ZTF is a wide-field astronomical survey at Palomar Observatory, California.

The comet’s green glow is from the effect of the Sun on cyanogen ((CN)2) and diatomic carbon.  The tail of a comet always points away from the Sun regardless of which direction the comet is moving.  This is due to radiation pressure from the Sun pushing on the comet’s dust particles which exceeds the pull of gravity.



Comet C2022 E3 as seen over Los Angeles.  A comet moves with a velocity unlike other fixed objects in the sky.  Superstitions can surround a comet and repute titles such as “Harbinger of Doom”.  Comet C-2022 E3 (shown above) is hurtling past Earth at 128,000 mph but is 26 million miles away and considered a long-period comet, last encountered during the ice age 50,000 years ago.   {R Lang & Assoc}1


If you have ever experienced discomfort when trying to view a comet, you are not alone.  Cultures throughout the ages have regarded comets as “omens of disaster” and “messengers of the gods”.  But in the light of science, comets are relatively bright objects spotted well in advance when approaching our solar system.  C2022 E3 was discovered eleven months prior and can presently be seen overhead with the unaided eye or small telescope.



1.  Since comets are fast moving objects, even at large distances, they can blur if not photographed with short exposures.  The above image was photographed with a single 45-second exposure at medium gain using a CCD-type camera cooled to -30o C, attached to a telescope.  (Gain is an equivalent to ISO setting which originated from film cameras).