ALPO COMET NEWS FOR May 2016
2016-May-2
Evening Comets
C/2014 S2 (PANSTARRS) [Perihelion on 2015-Dec-09 at 2.10 AU from the Sun]
Now 5 months past perihelion, this relatively large perihelion long-period comet is still bright enough for visual observation. I was able to observe it last night (May 2.3 UT) in 30×125 binoculars at magnitude 10.2. This May its range from the Sun and Earth increases from 2.67 to 2.89 AU and 2.30 to 2.85 AU, respectively. As a result it should fade by another 0.5 magnitude by the end of the month. It elongation in the evening sky falls from 100° to 82° degrees as its moves southward through Ursa Major (from a declination of +49° to +34°.
Morning Comets
252P/LINEAR [Perihelion 2016-Mar-15 at 1.00 AU]
252P/LINEAR has been a pleasant surprise this year. Not expected to get much brighter than 10th magnitude even while making an extremely close approach to Earth in late March (0.036 AU), the comet became a naked eye object for southern observers. The comet faded much slower than expected in April. Observations submitted to the Comet Section by Salvador Aguirre, Carl Hergenrother, John Sabia and Willian Souza showed the comet fading from magnitude ~6 to ~7 over the course of April. It remains a nice tailless weakly condensed fuzzball, but should continue to fade as its moves away from the Sun (1.19 to 1.44 AU) and Earth (0.24 to 0.47 AU) as it moves through Ophiuchus (May 1-25) and Hercules (25-31). Though technically a morning object, it is approaching opposition and can be observed late in the evening.
C/2013 X1 (PANSTARRS) [Perihelion on 2016-Apr-20 at 1.31 AU]
Until the past week or so, C/2013 X1 (PANSTARRS) had been too close to the Sun to be observed since February. This month PANSTARRS will move away from the glare of the Sun in the morning sky (elongation grows from 49° to 95° degrees). The comet spends May moving among the stars of Pisces (May 1-5) and Aquarius (5-31). Unfortunately, the comet is moving south of the Sun’s declination (-2° to -17°) making it an increasingly tough object for northern observers. Perihelion occurred back on April 20th. An increasing heliocentric distance (1.32 AU to 1.45 AU) will be countered by a decreasing geocentric distance (1.74 AU to 0.95 AU). Though the Section has not received any observations of this comet, recent observations submitted to the COBS website show the comet to be around magnitude 7.5. The decreasing Earth-comet range should help PANSTARRS brighten during May to magnitude 6.5 to 7.0. The comet will continue to brighten to perhaps magnitude 6.0 as it passes within 0.0.64 AU of Earth in late June.
New Discoveries
Since the last Comet Section News posting, three comet discoveries were reported though two of them were first seen in 2015.
C/2015 WZ (PANSTARRS) was discovered back on 2015 October 25 by the Pan-STARRS1 survey at a faint 21st magnitude. Further observations were made last November but due to a lack of obvious cometary activity it was designated as asteroid 2015 WZ. Artyom Novichonok of Russia reported cometary activity on April 17 on images taken with a 0.5-m f/2 telescope. At that time the comet was a much brighter magnitude 13. Since then, there have a been a handful of CCD and visual brightness measurements suggesting the comet may be as bright as magnitude 10.5 to 12.0. C/2015 WZ is a dynamically old long-period comet with a period of 2700 years. Perihelion occurred on April 15 at 1.38 AU.
P/2015 HG16 (PANSTARRS) is another example of a comet discovered last year (seen in March and April 2015) and designated as an asteroid. On 2016 April 4, Pan-STARRS1 rediscovered the object as a comet. With a peak brightness of magnitude 20-21, HG16 will not be getting very bright. It is a short-period object with a period of 10.5 years and perihelion of 3.13 AU.
P/2016 G1 (PANSTARRS) is a Main Belt comet or activated asteroid. Its orbit is very non-cometary with a perihelion of 2.05 AU, semi-major axis of 2.58 AU, eccentricity of 0.21 and inclination of 11°. It was discovered by the Pan-STARRS1 telescope on April 1 at 20th magnitude.
As always, the Comet Section is happy to receive all comet observations, whether images, drawings or magnitude estimates.
- Carl Hergenrother (ALPO Comet Section Coordinator)
