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Tue, 10 Oct 2017


An ASASSN in our skies


 Track of Comet ASASSN during September 2017

A recently discovered comet is currently well-placed in UK skies. But although it has been called a 'binocular comet' because predictions show it to be fairly bright, it is extremely hard to see even with large instruments from the UK. However, it is an easier object photographically. 

The comet was discovered in July by an automated supernova search survey, the "All-Sky Automated Survey for Supernovae" (ASASSN) at Cerro Tololo Inter-American Observatory in Chile – hence the odd name, which caused consternation among those whose task it is to name a comet. (Note the spelling if you search online!) Its designation is C/2017 O1. When discovered it was 15th magnitude, but as it has neared the Sun it has brightened and is now around magnitude 8.

It is moving slowly through the stars of Perseus and reaches its greatest brightness of about magnitude 7.5 in mid October. So it will be in an increasingly accessible part of the sky for some time to come. Perseus is rising in the east after midnight, and the comet is well-placed in the evening sky around midnight. It always remains beyond the orbit of Mars, and will not get close to us. It has an orbital period of around 3600 years, so won't be back in the vicinity of the Sun until the 57th century!

Although stars of magnitude 7 or 8 are easily visible in binoculars, a comet of this brightness is usually less easy to see as its brightness is spread out over a wider area and is not a point source. So fairly dark skies will be needed for the best views. Although photos from dark-sky sites show the comet to be close to its predicted brightness, in typical UK skies the comet is much harder to see, if not impossible. SPA Forum member was unable to find it using a 14-inch telescope from Galloway on 1 October.

The chart at top shows the region through which Comet ASASSN travels, with the horizon as seen at about 10 pm BST in mid October. The area is easy to find, with the bright star Aldebaran and the well-known Pleiades or Seven Sisters cluster as signposts. Click on the chart to get a detailed track, with stars shown to magnitude 8. The maps were generated using the SkyMap program. For a table of predicted positions see below the Gallery.

Gallery

Comet photo by Paul Sutherland

A photo of Comet ASASSN taken on 20 September from Kelling Heath, Norfolk. Robin Scagell used a Canon 70D camera through an 80 mm refractor to take 10 1-minute shots which he then stacked on the comet. Slight cloud during the exposure resulted in footprint-like star trails!

Here are predicted positions provided by the JPL Small-Body Database. Note that the positions are for 00.00 UT on each day, so from the UK at 00.30 BST on the day in question, for example, the comet will be very nearly at the position for the next day. Two sets of RA and Dec positions are given, the first being for plotting on printed star charts for epoch 2000.0, the second being for computer-generated sky maps or telescope handsets which use the epoch of date (ie allowing for precession). If this means nothing to you, just use our star map! The m in some rows indicates the presence of moonlight.

 Date__(UT)__HR:MN     R.A._(ICRF/J2000.0)_DEC R.A.__(a-apparent)__DEC
**********************************************************************
$$SOE
 2017-Aug-27 00:00     03 34 17.05 +05 51 59.3 03 35 12.91 +05 55 26.1
 2017-Aug-28 00:00     03 35 48.52 +06 27 22.7 03 36 44.60 +06 30 47.5
 2017-Aug-29 00:00     03 37 19.74 +07 03 29.0 03 38 16.06 +07 06 51.8
 2017-Aug-30 00:00     03 38 50.73 +07 40 19.4 03 39 47.29 +07 43 40.2
 2017-Aug-31 00:00     03 40 21.47 +08 17 55.0 03 41 18.29 +08 21 13.7
 2017-Sep-01 00:00  m  03 41 51.97 +08 56 16.8 03 42 49.05 +08 59 33.4
 2017-Sep-02 00:00  m  03 43 22.24 +09 35 25.9 03 44 19.58 +09 38 40.5
 2017-Sep-03 00:00  m  03 44 52.25 +10 15 23.5 03 45 49.87 +10 18 36.0
 2017-Sep-04 00:00  m  03 46 22.03 +10 56 10.5 03 47 19.93 +10 59 21.0
 2017-Sep-05 00:00  m  03 47 51.55 +11 37 48.0 03 48 49.74 +11 40 56.5
 2017-Sep-06 00:00  m  03 49 20.82 +12 20 17.1 03 50 19.30 +12 23 23.5
 2017-Sep-07 00:00  m  03 50 49.84 +13 03 38.7 03 51 48.61 +13 06 43.0
 2017-Sep-08 00:00  m  03 52 18.60 +13 47 53.8 03 53 17.68 +13 50 55.9
 2017-Sep-09 00:00  m  03 53 47.08 +14 33 03.3 03 54 46.48 +14 36 03.2
 2017-Sep-10 00:00  m  03 55 15.28 +15 19 07.9 03 56 15.01 +15 22 05.8
 2017-Sep-11 00:00  m  03 56 43.20 +16 06 08.6 03 57 43.27 +16 09 04.3
 2017-Sep-12 00:00  m  03 58 10.81 +16 54 06.0 03 59 11.23 +16 56 59.5
 2017-Sep-13 00:00  m  03 59 38.11 +17 43 00.8 04 00 38.90 +17 45 52.1
 2017-Sep-14 00:00  m  04 01 05.07 +18 32 53.5 04 02 06.25 +18 35 42.6
 2017-Sep-15 00:00  m  04 02 31.69 +19 23 44.5 04 03 33.26 +19 26 31.6
 2017-Sep-16 00:00     04 03 57.95 +20 15 34.3 04 04 59.93 +20 18 19.2
 2017-Sep-17 00:00     04 05 23.83 +21 08 23.0 04 06 26.23 +21 11 05.8
 2017-Sep-18 00:00     04 06 49.32 +22 02 10.7 04 07 52.14 +22 04 51.4
 2017-Sep-19 00:00     04 08 14.41 +22 56 57.4 04 09 17.67 +22 59 35.9
 2017-Sep-20 00:00     04 09 39.07 +23 52 42.9 04 10 42.78 +23 55 19.2
 2017-Sep-21 00:00     04 11 03.31 +24 49 26.8 04 12 07.48 +24 52 00.9
 2017-Sep-22 00:00     04 12 27.10 +25 47 08.5 04 13 31.75 +25 49 40.4
 2017-Sep-23 00:00     04 13 50.43 +26 45 47.4 04 14 55.59 +26 48 17.1
 2017-Sep-24 00:00     04 15 13.29 +27 45 22.4 04 16 18.97 +27 47 49.9
 2017-Sep-25 00:00     04 16 35.67 +28 45 52.5 04 17 41.89 +28 48 17.8
 2017-Sep-26 00:00     04 17 57.55 +29 47 16.3 04 19 04.34 +29 49 39.4
 2017-Sep-27 00:00     04 19 18.92 +30 49 32.2 04 20 26.29 +30 51 53.1
 2017-Sep-28 00:00     04 20 39.76 +31 52 38.4 04 21 47.74 +31 54 57.2
 2017-Sep-29 00:00     04 22 00.04 +32 56 33.0 04 23 08.66 +32 58 49.6
 2017-Sep-30 00:00     04 23 19.76 +34 01 13.5 04 24 29.03 +34 03 28.0
 2017-Oct-01 00:00  m  04 24 38.89 +35 06 37.6 04 25 48.83 +35 08 50.0
 2017-Oct-02 00:00  m  04 25 57.40 +36 12 42.5 04 27 08.05 +36 14 52.8
 2017-Oct-03 00:00  m  04 27 15.26 +37 19 25.2 04 28 26.64 +37 21 33.4
 2017-Oct-04 00:00  m  04 28 32.45 +38 26 42.6 04 29 44.58 +38 28 48.7
 2017-Oct-05 00:00  m  04 29 48.92 +39 34 31.3 04 31 01.83 +39 36 35.3
 2017-Oct-06 00:00  m  04 31 04.64 +40 42 47.7 04 32 18.37 +40 44 49.6
 2017-Oct-07 00:00  m  04 32 19.56 +41 51 28.0 04 33 34.15 +41 53 27.8
 2017-Oct-08 00:00  m  04 33 33.63 +43 00 28.3 04 34 49.11 +43 02 26.0
 2017-Oct-09 00:00  m  04 34 46.79 +44 09 44.4 04 36 03.20 +44 11 40.0
 2017-Oct-10 00:00  m  04 35 58.97 +45 19 12.0 04 37 16.36 +45 21 05.6
 2017-Oct-11 00:00  m  04 37 10.10 +46 28 46.7 04 38 28.52 +46 30 38.4
 2017-Oct-12 00:00  m  04 38 20.10 +47 38 24.1 04 39 39.60 +47 40 13.9
 2017-Oct-13 00:00  m  04 39 28.89 +48 47 59.4 04 40 49.51 +48 49 47.3
 2017-Oct-14 00:00  m  04 40 36.38 +49 57 28.0 04 41 58.17 +49 59 14.1
 2017-Oct-15 00:00     04 41 42.47 +51 06 45.3 04 43 05.48 +51 08 29.6
 2017-Oct-16 00:00     04 42 47.07 +52 15 46.4 04 44 11.35 +52 17 29.0
 2017-Oct-17 00:00     04 43 50.06 +53 24 26.8 04 45 15.67 +53 26 07.7
 2017-Oct-18 00:00     04 44 51.34 +54 32 41.8 04 46 18.34 +54 34 21.0
 2017-Oct-19 00:00     04 45 50.77 +55 40 26.9 04 47 19.24 +55 42 04.5
 2017-Oct-20 00:00     04 46 48.24 +56 47 37.6 04 48 18.25 +56 49 13.6
 2017-Oct-21 00:00     04 47 43.60 +57 54 09.7 04 49 15.23 +57 55 44.1
 2017-Oct-22 00:00     04 48 36.69 +58 59 59.1 04 50 10.04 +59 01 32.0
 2017-Oct-23 00:00     04 49 27.36 +60 05 01.7 04 51 02.51 +60 06 33.2
 2017-Oct-24 00:00     04 50 15.42 +61 09 13.9 04 51 52.48 +61 10 44.1
 2017-Oct-25 00:00     04 51 00.68 +62 12 32.0 04 52 39.74 +62 14 01.0 


 

Added by: Robin Scagell