OASI: C/2011 L4

Comet C/2014 L4 (PANSTARRS) is a non-periodic comet discovered in June 2011 in an image taken by the Pan-STARRS telescope, located on Maui in Hawaii. (PANSTARRS is short for Panoramic Survey Telescope and Rapid Response System.) It became visible to the naked eye when near perihelion in March 2013. OASI members Mike Harlow and Andrew Robertson reported observations of the comet starting on 13 March 2013 as follows.

13 March 2013, Mike Harlow. As the sky cleared just after sunset I thought I would look for the comet. Couldn’t see it with the naked eye but it was obvious very low in the west with 12x50 binoculars. Also quite easy to photograph. See figure 1.

13 March 2013, Andrew Robertson. Got a view of the comet visually. I'd set up my 150 mm refractor (Vixen Atlux 150 ED f9) on the front drive (only place I could get a view to the western horizon) and set the RA and Dec circles using the sun. Of course I'd only aligned the mount approximately with a compass. At 18:37 UT, I found PANSTARRS in the 9x50 finder and centred it to get a view through the main instrument. A 40 mm Pentax eyepiece gave x34 magnification and 1.9° FOV revealing a very bright, almost stellar, core, somewhat elongated. There was some dust/coma around the head and a very long and narrow tail. I upped to a 22 mm Pan eyepiece (x61 magnification and 1.1° FOV); it showed the tail extending from the centre about ⅓ to ½ the way to the edge of the FoV, stronger on the left hand side (inverted view). Tail very bright. Tried a comet filter but that just killed it. Also picked up the comet in 15x70 binoculars. By 19:05 UT, lost visibility of the comet in some bushes just above the horizon. In summary: a very brief and enjoyable observation!

06 April 2013, Mike Harlow. Comet PANSTARRS is now well placed in the dark morning sky and easy to find before it starts to get light. It is slowly moving north and this will help offset its gradual fade over the coming weeks. I imaged it around 4.00am (BST) on Saturday 06 April (when close to M31) with a DSLR and 200 mm lens (20x30 second exposures at f/5.6 and ISO 1600). See figure 2.

29 April 2013, Andrew Robertson. Figure 3 is my sketch made on 29 April 2013. The 2^nd tail seems more prominent now and at an angle of about 120° now rather than 100° as it was when I first observed it. There also appears to be more "striation" within the in-fill. The comet is fainter now but higher in a darker sky and with a tracking telescope presented a very enjoyable view.

30 April 2013, Mike Harlow. Comet PANSTARRS continues to move north and has now crossed the border from Cassiopeia into Cepheus. It is 228 million kilometres (about 1.53 AU) from Earth. It is still a binocular object and could easily be seen in 12x50’s at about 10.30pm BST. I obtained two sets of images (at about 11.00pm) with a Canon 550 DSLR. Figure 4, taken with a 200 mm lens, shows the comet amongst the stars of south-west Cepheus. (The large black silhouette is an ash tree that prevented imaging early in the comet's apparition!). Figure 5, taken with a 11.5 cm F/5 Newtonian, is a 1° square field with a small negative inset (in the full image) to show the curious "spike" that has been present for some time.

06 May 2013, Mike Harlow. Comet PANSTARRS continues to move north in Cepheus and is now within reach of my observatory and 30 cm F/4.1 telescope. Figure 6, a rather noisy image obtained on Monday night (06 May), shows the now familiar broad fan shape. (The figure is processed from 24x30 second sub-images with a luminance filter.) Ignore the dark bands in the comet’s tail: they are artefacts from the CCD - oops! Note the image scale: at 40 arcminutes square the field of view is bigger than the apparent size of the full moon... and the comet is now over 1.5 AU from Earth!

12 May 2013, Mike Harlow. After rain earlier in the night the sky cleared and it was very dark and transparent on Sunday morning (12 May) between about 1.00 and 2.00am. Comet PANSTARRS was easily visible in 12x50 binoculars so I thought I should try to image it again. I didn’t have time to set up the 30 cm telescope and CCD so I just took some DSLR shots through the 11 cm F/5 Newtonian. I converted the raw files to black and white and then stacked the images to take account of the comet’s motion of 2 arcmin per hour almost due north. If anything, the angle of the fan shaped tail is getting even wider. The bright star just on the top edge of the wide-field view (figure 7) is γ Cephei. The one degree square view (figure 8) is taken from the same set of images but shown as a negative and "stretched" more in contrast in an attempt to show the full extent of the comet's tail.

14 May 2013, Mike Harlow. I captured another set of images of PANSTARRS as it passed γ Cephei early this morning. Conditions were not as good as Sunday morning (12 May) and the sky looked distinctly grey at times so it was a struggle to pick out much of the faint tail. I captured CCD frames and generated figures 9-11 below by processing them in different ways. Figure 9 is stacked on the stars and shows the comet trailed, figure 10 is stacked on the comet to sharpen up details of the tail and figure 11 is a negative view of the comet with contrast stretched. The bright star lower left in figures 9 & 10 is γ Cephei. The gap in the star trails is when the cloud just became too thick to capture useful images.

The telescope used is an upgrade of my early 1980s 30 cm Newtonian with an Astro Systeme Austria (ASA) Wynne corrector which gives a flat, coma-free field. It covers a 50 mm diameter field so could be used with a much bigger CCD or full frame DSLR. (I’m currently using just a 15x15 mm Starlight Xpress H16 with 2048x2048 pixels).

Fig. 1. 13 March 2013.