Five hundred-metre-wide asteroid 2017 CS passes just 1.9 million miles (3 million kilometres) or 7.9 lunar distances away from Earth on the afternoon of Monday 29 May 2017. For a few nights around this date the 13th-magnitude body is well placed for Northern Hemisphere observers as it gallops through the constellations of Canes Venatici, Boötes and Hercules at a rate of up to 14 degrees/day. Click image to be taken to an interactive Java applet. Image credit: Orbit Viewer applet originally written and kindly provided by Osamu Ajiki (AstroArts), and further modified by Ron Baalke (JPL) / Ade Ashford (AN).Before the waxing crescent Moon of the next lunation gets too bright, Northern Hemisphere observers get the chance to track a relatively bright and recently discovered Amor-type asteroid that passes just 0.02037 astronomical units (1.893 million miles, or 7.93 lunar distances) from Earth at 15:43 UT (4:43pm BST) on Monday 29 May 2017.
Believed to be between 350 metres and 780 metres in diameter and orbiting the Sun every 4.21 years, near-Earth asteroid 2017 CS was discovered by Pan-STARRS 1 on 2 February 2017. Photometric results indicate a rotation period of about 40⅓ hours with a lightcurve amplitude of 0.18.This wide-field view shows the track of near-Earth asteroid 2017 CS from 29 May to 1 June with positions at 0h UT (1am BST) during the period that it lies closest to Earth. The body moves in excess of 40 degrees through the constellations of Canes Venatici, Boötes and Hercules during the interval in question, a region of sky that lies high in the southern sky of the British Isles around midnight. For scale, this chart is almost 60 degrees wide, or approximately three spans of an outstretched hand at arm’s length. Detailed finder charts for observers in the UK and Western Europe can be found below. AN graphic by Ade Ashford.Given its size and proximity, 2017 CS could attain magnitude +13.5 at closest approach if the predictions tabulated at the bottom of this page hold true. This means that the asteroid is a viable target for 6-inch (15-cm) and larger telescopes as it moves against the background stars at a rate equivalent to the apparent width of the full Moon every hour.Captured in nautical twilight from a suburban backyard on Friday 26 May 2017 at 22:18 UT, near-Earth asteroid 2017 CS glimmers at magnitude +14.5 in this five-minute exposure, leaving a trail 2 arcminutes long against the background stars of northeastern Leo. At the time, 2017 CS was moving at a rate of 9.6 degrees per day, still 2¾ days from its close encounter with our planet. For scale, this negative view is about 25 arcminutes (0.4°) wide and the faintest stars shown are around magnitude +17. Ade Ashford used a HyperStar-equipped Celestron C11 at f/2 with a Starlight Xpress Ultrastar C camera.Astronomical twilight now lasts all night for observers in the British Isles, except for those in the southernmost counties of England, so the darkest skies are found between midnight and 2am BST. The light of the waxing cresent Moon will also start to interfere from 31 May.
For observers in Western Europe, the following four detailed finder charts for successive nights around the time of closest approach should help you track down this fascinating small world.
Chart 1: 29 May — covering 11pm BST on 28 May to 3am BST on 29 MayThis detailed finder chart shows the motion of asteroid 2017 CS against the background stars of Canes Venatici over the course of four hours starting at 22h UT (11pm BST) on 28 May. The 3-degree-wide field shows stars down to magnitude +14.5 centred on α=13h 26.0m, δ=+37° 02’ (J2000.0). Click the graphic for a greyscale version suitable for printing and use at the telescope. AN graphic by Ade Ashford.
Chart 2: 30 May — covering 11pm BST on 29 May to 3am BST on 30 MayThis detailed finder chart shows the motion of asteroid 2017 CS against the background stars of Boötes over the course of four hours starting at 22h UT (11pm BST) on 29 May. The 3-degree-wide field shows stars down to magnitude +14.5 centred on α=14h 38.1m, δ=+42° 06’ (J2000.0). Click the graphic for a greyscale version suitable for printing and use at the telescope. AN graphic by Ade Ashford.
Chart 3: 31 May — covering 11pm BST on 30 May to 3am BST on 31 MayThis detailed finder chart shows the motion of asteroid 2017 CS against the background stars of Hercules over the course of four hours starting at 22h UT (11pm BST) on 30 May. The 3-degree-wide field shows stars down to magnitude +14.5 centred on α=15h 55.0m, δ=+43° 58’ (J2000.0). Click the graphic for a greyscale version suitable for printing and use at the telescope. AN graphic by Ade Ashford.
Chart 4: 1 June — covering 11pm BST on 31 May to 3am BST on 1 JuneThis detailed finder chart shows the motion of asteroid 2017 CS against the background stars of Hercules over the course of four hours starting at 22h UT (11pm BST) on 31 May. The 3-degree-wide field shows stars down to magnitude +14.5 centred on α=17h 01.6m, δ=+42° 55’ (J2000.0). Click the graphic for a greyscale version suitable for printing and use at the telescope. AN graphic by Ade Ashford.
Astronomers at Goldstone (and possibly Arecibo) plan to make radar observations of 2017 CS in late May that could yield a surface resolution of 3¾ metres if the signal-to-noise ratios are strong enough.
If you miss 2017 CS this time around, its next close encounter with Earth occurs on 17 May 2038 when the asteroid passes 0.0249 astronomical units, or 2.3 million miles (9.7 lunar distances) from our planet.
The Minor Planet Center classifies 2017 CS as a “Potentially Hazardous Asteroid.”
The table above shows the hourly positions of asteroid 2017 CS for the interval that it is visible in a sufficiently dark sky from the UK during the period that it is closest to Earth. Universal Time (UT) is used, so add one hour to convert to British Summer Time. Equatorial coordinates are given for both J2000.0 and the current epoch (J2017.4), the latter being useful for entering into digital setting circles or GoTo mount hand controllers. The asteroid’s distance in astronomical units (Delta), visual magnitude (Mag.), rate of motion (in degrees/day) and constellation (Con) of residence is also shown hourly. Data credit: Minor Planet Center / NASA HORIZONS / Ade Ashford.
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