Wednesday 10 May 2017

Comet C/2015 ER61 (PANSTARRS) reaches perihelion.

Comet C/2015 ER61 (PANSTARRS) will reach its perihelion (the closest point on its orbit to the Sun) on Wednesday 10 January 2017, when it will be approximately 1.04 AU from the Sun (i.e. 104% of the distance between the Earth and the Sun, slightly outside the Earth;s orbit), though it will not be particularly close to us, being about 90° ahead of us on the Earth's orbit. The comet will be in the constellation of Pisces seen from the Earth, though it will not be naked eye visible.

Composite image of Comet C/2015 ER61 (PANSTARRS) composed from nine 60-second exposure images of the object taken with the TENEGRA III Telescope at he Tenegra Observatory in Arizona on 7 April 2017. Gianluca Masi/Virtual Telescope/Michael Swartze/Tenegra Observatory.

C/2015 ER61 (PANSTARRS) was discovered on 15 March 2015 by the University of Hawaii's PANSTARRS telescope. The name C/2015 ER61 (PANSTARRS) implies that it is a non-periodic comet (C/) (all comets are, strictly speaking, periodic since they all orbit the Sun, but those with periods longer than 200 years are considered to be non-periodic), that it was the 1542nd comet (comet R61) discovered in the first half of March 2015 (period 2015 E), and that it was  discovered by the PANSTARRS telescope.

The calculated orbit of C/2015 ER61 (PANSTARRS) . The Sky Live/3D Solar System Simulator.

C/2015 ER61 (PANSTARRS) has a 7591 year period and a highly eccentric orbit tilted at an angle of 6.35° to the plain of the Solar System, that brings it to 1.04 AU from the Sun at perihelion and to 2456 AU (2456 times as far from the Sun as the Earth) at aphelion. This is 253 times as far from the Sun as the planet Neptune, and 152 times as far from the Sun as the outer edge of the Kuiper Belt, but still only touching the inner boundary of the Oort Cloud.

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