Near-Earth asteroid 164121 (2003 YT1) was 0.0355 astronomical units (5.3 million kilometres; 3.3 million miles) from Earth and travelling at almost 31 kilometres/second when captured in this 460-second exposure starting at 21:40 UT on 31 October. The eleventh-magnitude asteroid’s trail is 7¼ arcminutes (0.12 degrees) long. The bright star is sixth-magnitude HD36496 in the constellation of Camelopardalis. At 2:30am GMT on 2 November, 2003 YT1 passes less than one-tenth of a degree from Polaris, the pole star. Image details: Ade Ashford used a Starlight Xpress Ultrastar C camera coupled to a Hyperstar-enabled Celestron C11.It would seem that All Hallows’ Eve is a good time to spot near-Earth objects (NEOs). In 2015 we had the close passage of an appropriately skull-shaped dead comet, designated 2015 TB145, that missed our planet by just 1.3 lunar distances, or about 302,000 miles (486,000 kilometres). This year, it’s the turn of asteroid 164121 (2003 YT1) to pass Earth by a somewhat safer margin — 3.2 million miles (5.2 million kilometres) at 9:24am GMT on 31 October 2016.
NEO 164121 (2003 YT1) is a 1.7-kilometre-(1.1-mile)-wide Apollo asteroid discovered by the Catalina Sky Survey on 18 December 2003. It completes an orbit every 427 days in a somewhat eccentric ellipse that carries it to within 73 million miles (118 million kilometres) of the Sun. The asteroid also has an orbit with a relatively high inclination of 44 degrees, which has interesting consequences for the object’s visibility over the next few days.This chart shows the track of near-Earth asteroid 164121 (2003 YT1) from 30 October to its close brush with Polaris at 2:30am GMT on 2 November 2016. It covers the period during which the eleventh-magnitude object is closest to Earth (9:24am GMT on 31 October) and moving at almost 23 degrees/day through northern Auriga. Thereafter, 2003 YT1 traverses the constellation of Camelopardalis (the Giraffe), briefly dips into Cepheus (the King) on 1 November, then has its aforementioned close encounter with Polaris, passing less than one-tenth of a degree from the pole star. The chart is 60 degrees wide, or about three spans of an outstretched hand at arm’s length. Stars are shown down to the sixth magnitude. See below for a detailed finder chart and UK-centred ephemeris. Click the graphic for a greyscale version suitable for printing. AN graphic by Ade Ashford.As the last day of October 2016 dawns, 2003 YT1 is already a circumpolar object for observers in the British Isles where it will remain above the horizon 24/7 until the third week of November. The asteroid’s motion is northerly, almost entirely in declination at the present time.
Photographing 2003 YT1 near Polaris: no expensive tracking mounts required!
As seen from the heart of the British Isles, 2003 YT1 passes just 4.6 arcminutes — less than one-tenth of a degree — from Polaris at 02:30 UT (2:30am GMT) on 2 November. Since this near-Earth asteroid passes so close to the pole star, an interesting astrophotographic opportunity presents itself: almost anyone with a tripod-mounted DSLR camera who can get to a dark sky site can have a go at capturing 2003 YT1.Near-Earth asteroid 164121 (2003 YT1) is poised to pass just 4.6 arcminutes — less than one-tenth of a degree — from Polaris at 02:30 UT (2:30am GMT) on 2 November. This detailed finder chart shows an area of sky centred on Polaris that is 2 by 2⅔ degrees in extent, corresponding to the field of view of a typical telescope at 20x magnification. The track of the magnitude +11.9 asteroid is shown for the centre of the British Isles at the stated Universal Times (UT ~ GMT). Stars down to the fourteenth-magnitude are shown, roughly the limit of a 12-inch aperture telescope. Click the graphic for a greyscale version suitable for printing. AN illustration by Ade Ashford.Any object passing this close to the north celestial pole will be almost stationary in the sky for the duration of an exposure that will be long enough to record it. An 85mm lens, for example, used with a typical APS-C sensor DSLR will deliver a field of view almost 15 x 10 degrees in extent. (Our online DSLR Calc web app will enable you to work out the field of view of other lens/camera combinations.) Recall that the asteroid passes less than one-tenth of a degree from Polaris at closest approach, so the use of a longer focal length lens means that the NEO’s faint trail is less likely to be lost in the glare of the pole star.
Simply focus your chosen DSLR lens on infinity at full aperture (you can use a distant landmark during the daytime for this, being careful not to disturb the focus of the lens until nightfall), set the ISO rating to 800 or 1600, point at Polaris and shoot some 30 second, 1 or 2-minute exposures with a cable release. If you have the appropriate software on your computer, stacking several of these carefully registered images (each of the same exposure time) will improve signal-to-noise ratio and 2003 YT1 will be identified as the dot that moves between images.
Viewing 2003 YT1 near Polaris
If you are fortunate to have clear skies around 02:00 UT (2am GMT) on 2 November, note that this is a rare opportunity for users of undriven telescopes such as Dobsonians to observe an object at length without the need for tracking. In fact, owners of telescopes on alt-azimuth mounts are at a distinct advantage here since equatorial mounts are more difficult to use so close to the celestial pole.
If you have a telescope with an aperture of 6-inches (150-millimetres) or larger, get Polaris within the field of view of your medium- to high-power eyepiece close to the appointed time and look for the twelfth-magnitude speck of light that is 2003 YT1 moving against the background stars of Ursa Minor at a rate of 12 degrees per day, or half a lunar diameter per hour.
Ephemeris of 2003 YT1 for the UK This hourly topocentric ephemeris of 2003 YT1 is computed for the asteroid’s period of visibility from the centre of the British Isles. Observers with computerised GoTo mounts or digital settings circles can enter these J2000.0 epoch coordinates directly with negligible parallax error for the whole of the UK. Computing credit: JPL’s HORIZONS system.
Inside the magazine
For a comprehensive guide to observing all that is happening in the current month’s sky, tailored to Western Europe, North America and Australasia, obtain a copy of the November 2016 edition of Astronomy Now.
One of best deep-sky objects of the approaching season is the Andromeda Galaxy, or Messier 31, that is now accessible low in the east-northeast by 10pm local time in the UK and Western Europe. Here’s our comprehensive guide to locating this iconic Local Group galaxy.
Surrounded by an envelope of dust, the subject of this NASA/ESA Hubble Space Telescope image is a young pre-main-sequence star known as HBC 1. The star is in an immature and adolescent phase of life, hence its classification — most of a Sun-like star’s life is spent in a stage comparable to human adulthood dubbed the main sequence.
At around magnitude +9, C/201 W2 (Africano) is the brightest comet currently on show, passing closest to Earth on 27 September slightly less than half an astronomical unit away. Speeding through the constellations of Pegasus, Pisces and Aquarius, Comet Africano also lies within a binocular field of view of outermost planet Neptune on the night of 3–4 October.
