With respect to the flyby of 400 meter diameter asteroid 2005YU55 with 0.7 lunar distances on Nov. 8, this note contains ephemeris and local circumstances information to observe the asteroid from an urban SLC location. NASA-JPL provides the following schematic of the flyby as seen from the North Ecliptic Pole - NASA animated schematic of the flyby seen from the North Ecliptic Pole http://www.jpl.nasa.gov/images/comet/20110502/comet20110502.gif - which translates from a SLC observing point into the asteroid streaking through 60 degrees of Pegasus between 7pm and 12 midnight _MST_ on Tuesday, Nov. 8., beginning north of Enif and ending near the center of the Pegasus Square. Wide-field view of path of 2055YU55 from SLC UT http://www.slas.us/gallery2/main.php?g2_itemId=4743 The observing circumstances will be the flyby will occur at the time of a near full Moon, and the Moon will be about 90 degrees from 2055YU55's first point of visibility above Enif. Because the asteroid is approaching and crossing the Earth's orbital path from the sun-side, 2005YU55 will not be optically visible during the days leading up to its closest approach; the asteroid will only be visible on the night that it crosses Earth's orbital path and enters the anti-solar side of Earth's view (see NASA animation, above). After it first becomes visible between 7pm and 8pm, the asteroid will appear to move towards the Moon through 11pm. From the NASA-JPL Horizons ephemeris applet, the predicted magnitude of the asteroid (v 11.0) and its hourly position are shown in Tables A and B below; however, predicted asteroid magnitudes are highly variable. The asteroid may actually be several magnitudes dimmer or brighter than the prediction. Also note that Mountain Standard Time begins on Nov. 6, 2011 at 1:00am. Remember to adjust your watches and GMT offsets accordingly. Given the near full Moon and the uncertain magnitude of the asteroid, seeing the asteroid is not guaranteed, but the last similar asteroid passage that I saw was interesting enough to make taking a try at seeing 2005YU55 worth the effort. After reviewing the asteroid's path, I have concluded that the best visual acquisition time is at 10:15pm _MST_, when the asteroid cross the constellation line between alf Peg and bet Peg within an acquisition field that is well delineated by magnitude 6 and 7 stars. My proposed acquisition field is about 6 degrees north of alf Peg (Markab) and is described in the following charts and in List A below. Note that the asteroid is moving very quickly and will cross a 1 degree acquisition field of view in less than 5 minutes. Mid-field view of acquisition field for 2055YU55 north of Markab at 10:15pm MST. http://www.slas.us/gallery2/main.php?g2_itemId=4746 Close-field view of the acquisition field for 2055YU55 north of Markab at 10:15pm MST. http://www.slas.us/gallery2/main.php?g2_itemId=4749 Although there is no probability that the 1400 meter asteroid will hit either the Earth or the Moon, if the asteroid had hit the Earth, it would make about a 13km dia. crater, and if it hit the Moon it would make about a 20 km dia. crater, per Melosh's Earth Impacts and Projectile Size calculators. http://www.lpl.arizona.edu/tekton/crater_p.html http://impact.ese.ic.ac.uk/ImpactEffects/ Happy hunting and Clear Skies - Kurt Addenda Table A. Mtn. Standard Times - GMT Offset -7 hours beginning effective Nov. 6, 2011 1:00 am UT Date-Time | J2000 RA DEC | Az | Alt | Predicted Mag 20111108 7:00pm | 21 48 40.99 +15 03 14.3 | 177.0941 | 64.3327 | 11.26 20111108 08:00pm | 22 17 37.66 +16 27 26.7 | 194.9493 | 65.1218 | 11.16 20111108 09:00pm | 22 43 27.62 +17 28 19.1 | 213.6427 | 63.3986 | 11.12 20111108 10:00pm | 23 06 06.30 +18 10 04.1 | 230.2226 | 59.2258 | 11.13 20111108 10:15pm | 23 11 17.25 +18 18 03.3 | 233.8688 | 57.8575 | 11.14 20111108 11:00pm | 23 25 45.71 +18 37 12.6 | 243.6415 | 53.1270 | 11.17 20111109 12:00am | 23 42 46.04 +18 53 42.6 | 254.4281 | 45.6795 | 11.22 Table B. UT Date-Times UT Date-Time | J2000 RA DEC | Az | Alt | Predicted Mag 20111109 02:00 | 21 48 40.99 +15 03 14.3 | 177.0941 | 64.3327 | 11.26 20111109 03:00 | 22 17 37.66 +16 27 26.7 | 194.9493 | 65.1218 | 11.16 20111109 04:00 | 22 43 27.62 +17 28 19.1 | 213.6427 | 63.3986 | 11.12 20111109 05:00 | 23 06 06.30 +18 10 04.1 | 230.2226 | 59.2258 | 11.13 20111109 05:15 | 23 11 17.25 +18 18 03.3 | 233.8688 | 57.8575 | 11.14 20111109 06:00 | 23 25 45.71 +18 37 12.6 | 243.6415 | 53.1270 | 11.17 20111109 07:00 | 23 42 46.04 +18 53 42.6 | 254.4281 | 45.6795 | 11.22 List A. Acquisition field alignment stars for 10:15pm field north of alf Peg ( Local high-precision alignment star - alf Peg Markab SAO 108378 The 10:15pm MST acquisition field is about 6 degs north of Markab. Acquisition field alignment stars are: SAO108400 v6.1 Celestial East side of acquisition field SAO108382 v7.1 Celestial North side of acquisition field SAO108397 v7.3 Celestial South side of acquisition field