Comet 2017 S3 PANSTARRS

As I mentioned before we’re expecting some reasonably bright comets between now and the end of the year.

First up is C/2017 S3 PANSTARRS which is very well placed for observers like me in Northumberland.  Here is a finder chart for the next few weeks:

Finderchart for C/2017 S3 PANSTARRS.  Generated with PP3, LaTeX and PSTRicks.

Comet PANSTARRS is tracking south from Camelopardalis and through Auriga over the next couple of weeks.  From the UK PANSTARRS is circumpolar: always above the horizon and visible all night.  However the best views will be during the run up to sunrise when it is getting higher in the sky.

We can expect PANSTARRS to be at its best during the first week of August.  Magnitude estimates for comets are subject to a lot of uncertainty!  It is likely to reach magnitude +4, or maybe +3 (as bright as the Andromeda Galaxy).  Viewing will probably be against a moonlit sky and/or twilight.  Binoculars should pick it out easily by the end of July and it may be a naked eye object in early August.  You can find recent magnitude estimates here.

PANSTARRS is approaching perihelion during this period and also getting closer to Earth.  The comet will buzz past the bright stars Castor and Pollux in Gemini from August 4th – 6th; look for it low in the northeast an hour and half before sunrise.

PANSTARRS is at its closest to Earth on August 6th: 0.7579 AU (113 million km).

We’ll lose PANSTARRS in the morning twilight at the end of the first week of August and it will reach perihelion on August 15th at a distance of 0.2084 AU (31 million km) from the Sun.

C/2017 S3 PANSTARRS orbit. Credit: JPL Small Bodies Database

After perihelion the comet will be on the far side of the Sun and a dim telescopic object.  PANSTARRS is following a near parabolic orbit diving down from above the plane of the solar system and heading back out after perihelion.  It is a one-time visitor to the inner solar system and it won’t be back for at least many thousands of years!

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