near-Earth asteroid will be readily observable for Irish/UK observers between September 4-14 during which time it will exceed magnitude 15.0. It is probably between 200-500 m diameter. It will be brightest around September 10-12 when it will reach visual magnitude 13.6 on average. It passes closest to us around 05h UT on Sep 14 at a range of about 7.4 lunar-distances (0.019 AU).
2012 QG42 is a potentially hazardous asteroid (PHA) and is unusual in that it passes very close to the opposition point on September 7. The circumstances of this close approach therefore makes it a good target for photometry (using a V, R or r' filter if possible) as well as other physical studies. An ephemeris with visibility details for UK observers is available at:
If you are planning to observe this target then please consult the Minor Planet Center ephemeris service:
http://www.minorplanetcenter.net/iau/MPEph/MPEph.html to obtain exact positions for an observatory location near to your site at the time you require.