C/2013 US10 Catalina

Closest to Sun on 15 November 2015 at 0.82AU
Closest to Earth on 16 January 2016 at 0.72AU
Maximum magnitude 6 in Nov 2015 -Jan 2016

C/201 3US10 was discovered as an asteroid in October 2013 by the Catalina sky survey, hence the asteroid designation.
It was later shown to be travelling in a retrograde direction opposite to the planets (inclined 149 degrees to the ecliptic)
as well as in a parabolic orbit (eccentricity =1) more typical of a comet.
Sure enough, cometary activity was eventually detected.
Catalina is dynamically new, its first visit to the inner solar system. We know this via its original eccentricity.
It is also intrinsically bright, with a calculated absolute magnitude of 6.
Catalina had the potential to reach faint naked eye visibility between Oct 2015 to Jan 2016 but fell short of expectation
peaking at magnitude 6 when it arrived at perihelion on 2015 November 15 at a distance of 0.82AU from the Sun.
Unfortunately, this occurred when the comet was on the opposite side of the Sun.

However, Its retrograde orbit improved the odds for a close Earth passage, twice in this instance.
On August 14, 2015 the inbound comet passed 1.08AU from the Earth when it was situated in southern circumpolar skies.
Post perihelion and outbound, a more favourable encounter at 0.72AU occurred on January 16, 2016 when it was better situated for northern observers.

Dynamically new comets in general tend to disappoint.

They show initial promise at a large distance from the Sun, but then undergo intrinsic fading as they approach perihelion.
Classic past examples are Cunningham in 1941, Kohoutek in 1973, Austin in 1990 and ISON in 2013.

Observations below show the development of the comet.

C/2013 US10 Catalina
2015 Apr 19.82UT: m2=12.7, Dia = 0.5'. DC=8, Canon 60Da + Sigma lens. [White in appearance - highly condensed]

C/2013 US10 Catalina on 2015 August 8. Visual magnitude 7.5.

September 2015

At the start of September, the magnitude 7.0 comet was situated on the Norma Circinus border in the southwest after dusk.
The comet maintained a slow rate of brightening as it receded from Earth but approached the Sun.
On Sep 7-8, it was within a degree of star cluster NGC5822 in Lupus. Photo below taken Sep 5.


October 2015 plus night mode chart

As October 2015 began, the magnitude 6.5 comet was situated 4 degrees North of Eta Centauri.

The first 2 weeks of October offered the best southern viewing, as the comet rapidly approached evening twilight by months end.
Moonlight interfered from October 16.
The comet remained unobservable during November as it passed 8 degrees from the Sun on November 7, then reappeared in December morning skies for northerners.

On December 9, the magnitude 6.2 comet was located in Virgo, a few degrees to the north of Venus, very low in the Eastern morning sky at 4:30am.
Since the comet was heading directly northwards, conditions improved only gradually as the month progressed.

Image of comet Catalina on 2016 Dec 19 at 11:35UR.
Taken remotely using I-Telescope T20 in New Mexico.
Photo shows ion tail to upper right and dust trail to lower left.

On December 23, the comet was at 7 degrees altitude in the North-eastern sky, still situated in Virgo, at 0430am.
Moonlight started to interfere after this date.
The comet was heading for an Earth approach of 0.72AU on January 17th, but situated deep in northern skies by then.