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Sun, 27 Aug 2017


Comet ASASSN in our skies


 Track of Comet ASASSN during September 2017

A recently discovered comet will be visible in binoculars during the next couple of months. But when we say ‘visible’, don’t expect to see anything spectacular. If early images are anything to go by, this will be a faint blob rather than a mini version of Halley’s Comet.

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 9.

It is moving slowly through the stars of Taurus, and will remain there until the end of September, when it moves into Perseus and reaches its greatest brightness of about magnitude 7.5. So it will be visible in an increasingly accessible part of the sky for some time to come. Taurus and Perseus are rising in the east after midnight, and by October the comet will be well-placed in the evening sky around midnight, and visible earlier in the evening. The comet 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.

The chart at top shows the region through which Comet ASASSN travels, with the horizon as seen at about 1 am BST in late August. 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

The comet is at the centre of this (cropped) photo taken by Paul Sutherland on the morning of 28 August using a 50 mm lens on a Fuji X-M1 camera (90 sec at ISO 1600) from Walmer, Kent. The image is oriented as seen in the sky, with north to the upper left. 

Photo of comet ASASSN by Robin Scagell

In this photo by Robin Scagell, taken on the morning of 28 August, the comet is at centre right. He used an Atik 314L+ CCD camera on a Sky-Watcher 80 mm f/6.7 ED refractor, combining 35 mono 25-second exposures (14½ minutes total) with the stars and comet stacked separately. The bright star to upper right of the comet is magnitude 9.42, and the faintest stars shown are about 15th magnitude. This image has north at the top, 

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 rown 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