Comet 12P/Pons-Brooks is brightening and can be seen in the western sky after sunset with a good pair of binoculars and good viewing conditions (dark and clear).
Discovered in 1385, Comet Pons-Brooks returns every 71 years. Its ion tail, visible in deep camera exposures, is pushed by solar wind and points away from the Sun. The comet may brighten enough to be visible during the April 8 solar eclipse!
Comet 12P/Pons–Brooks:
Orbital period: 71 years
Diameter: ~34 km
Aphelion: 33.616 AU (Neptune is ~30 AU away)
Inclination: 74.2°
Discovery: 1812 at Marseilles Observatory by Jean-Louis Pons and on its next appearance in 1883 by William Robert Brooks
Pre-1812 observations: 1385, 1457, ...
Perihelion: 21 April 2024
Closest approach to Earth: 2 June 2024.
Apparent magnitude 6.5 and below are visible to the unaided eye, under good visibility conditions (objects with lower magnitude are brighter). Objects about 4 magnitudes fainter can be seen with binoculars.
Current brightness is around 5. Peak brightness is expected around the 3rd week of April.
Here is another stunning pic of Comet 12P/Pons–Brooks, taken by Fritz Helmut Hemmerich on April 9.
Also shown below is the image taken by Dan Bartlett on March 30, to help see how the comet shape has evolved over the past 10 days as it approaches the Sun.
Comet 12P/Pons–Brooks is very low in the evening sky now as it approaches perihelion, which will occur on April 21.
Please see the rest of this thread for additional info on this comet.
The green color seen in the coma of most comets, but not in their tails, is due to emissions from Diatomic carbon C2 (aka dicarbon) molecules.
Sunlight heats the comet’s ice and organic material to produce C2 molecules, which break apart in ~2 days before they reach the tail. C2 is excited by solar UV radiation and emits mostly in infrared but its triplet state radiates at 518 nm (d3Πg → a3Πu transition below).
Diatomic carbon is a green, gaseous inorganic chemical. It is unstable at ambient temp. and pressure (it polymerizes). It is found in flames, comets, stars and the interstellar medium. One study suggests the presence of a quad bond.
From https://www.pnas.org/doi/10.1073/pnas.2113315118 -
"This work shows that, to break the quadruple bond of C2 using sunlight, the molecule must absorb two photons and undergo two “forbidden” transitions." (spin conservation and the Born–Oppenheimer approx).
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C2 exhibits a triple bond as in N2, but has been shown to have a fourth weaker bond formed by the outer electrons. Emissions caused by Sunlight, the quad bond and bond dissociation energy levels result in the green color seen in the coma of most comets, but not in their tails.
This set of images was posted on the NASA APOD site on Apr 8. The images show comet 12P/Pons-Brooks's tail changing in shape and size over 9 days from March 6 to 14.
The images show the comet's dust and ion tails. The dust tail, consisting of vaporized ejecta from the comet, points away from the sun and slightly behind the comet, while the ion tail, made of ionized gases, points away from the Sun aligned with the solar wind.
This graphic from ESA illustrates the structure of a comet and its tails.
The dust tail contains tiny vaporized particles, which appear whitish yellow in the Sun’s light. The ion/plasma tail is made up of electrically charged gas, which emits a blue glow due to the presence of CO ions. The tails point away from the Sun, aligning with the solar wind; the dust tail curves along the comet path.
A hydrogen envelope surrounds the coma and tails visible only in UV light.
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