In December 2019 astronomers at ATLAS ( Asteroid Terrestrial-impact Last Alert System ) in Hawaii discovered Comet C/2019Y4, flagging it as one to watch come May 2020. Almost immediately C/2019Y4 became known as comet ATLAS. At first astronomers predicted May 31, 2020 as day to watch ATLAS pass within the orbit of Mercury and the Sun at 0.25 AU distance, culminating in spectacular brightness as dissolving heat set ATLAS ablaze.
This week astronomers watched in amazement as magnitude increased 4,000 fold from +17 in early February to +8 by mid-March, stunned by runaway magnitude several months ahead of perihelion (closest orbital approach to the Sun ). Magnitude is a measure of brightness observed from Earth, the lower the magnitude, the brighter the cosmic object. For perspective, faintest objects visible from Earth with binoculars have a magnitude of +9.5. Venus and Mars at their brightest, magnitude -4.4 and -3.0 respectively. More magnitude linked below –
“Comet ATLAS continues to brighten much faster than expected,” says Karl Battams of the Naval Research Lab in Washington DC. “Some predictions for its peak brightness now border on the absurd.”
According to Dr. Tony Phillips at https://spaceweatherarchive.com/2020/03/16/comet-atlas-is-brightening-faster-than-expected/ if ATLAS magnitude continues to bloom at this pace, by May it could range between +1 to -5, possibly brighter than Venus and visible to the naked eye in daylight.
Comet ATLAS (C/2019 Y4) photographed on March 6, 2020, by Austrian astrophotographer Michael Jäger. The comet’s diffuse green atmosphere is about twice as wide as the planet Jupiter.