C/2007 W1 (Boattini) is a long-period comet discovered on 20 November 2007, by Andrea Boattini at the Mt. Lemmon Survey.^[1] At the peak the comet had an apparent magnitude around 5.^[5]

On 3 April 2008, when C/2007 W1 was 0.66AU from the Earth and 1.7AU from the Sun, the coma (expanding tenuous dust atmosphere) of the comet was estimated to be as large as 10 arcminutes.^[6] This made the coma roughly 290,000 km in diameter.^[7]

On 12 June 2008, the comet passed within about 0.21005 AU (31,423,000 km; 19,525,000 mi) of the Earth.^[8] The comet came to perihelion (closest approach to the Sun) on 24 June 2008 at a distance of 0.8497 AU.^[3]

The comet has an observation arc of 285 days^[3] allowing a good estimate of the orbit. The orbit of a long-period comet is properly obtained when the osculating orbit is computed at an epoch after leaving the planetary region and is calculated with respect to the center of mass of the Solar System. Using JPL Horizons, the barycentric orbital elements for epoch 2020-Jan-01 generate a semi-major axis of 1,582 AU, an apoapsis distance of 3,163 AU, and a period of approximately 63,000 years.^[2][4]

Before entering the planetary region, C/2007 W1 had a hyperbolic trajectory.^[2] The comet was probably in the outer Oort cloud with a loosely bound chaotic orbit that was easily perturbed by passing stars.