The charts in this article will help North American observers locate two stars being occulted by asteroids in April.
On April 16th near 2:55 Universal Time (UT), minor planet 1309 Hyperborea hides a 7th-magnitude star in Cancer for up to 6 seconds. Hyperborea means "far north," and that's where the path has gone. The path is now expected to pass just north of Calgary, Alberta, where an event could occur but twilight might be too strong to find the star in time. Edmonton, Alberta, has even less of a chance of seeing the occultation. Observers in Saskatoon, Saskatchewan, are more likely to see the event, but with the Sun at an altitude of -7°, the bright sky will make it difficult to find the star (SAO 117121, spectral type K2).
Later the same week, within a few minutes of 7:48 UT on April 20th, 139 Juewa passes in front of a 10th-magnitude star in Virgo. The wide path includes the populous cities of Montreal, Detroit, Chicago, Denver (almost), and San Francisco. For skywatchers who are centered in the path, the combined light of the star and asteroid will dim by a full magnitude for about 16 seconds.
The finder charts given here go as faint as 11th magnitude and will help in locating the target stars. Many other occultations by asteroids were described by David W. Dunham in the March 2002 issue of Sky & Telescope, page 92. He explained that the predicted paths are often revised in the days leading up to an event.
If you're interested in timing occultations, be sure to refer to the article "How and Why To Make Occultation Timings" elsewhere on this Web site. Finder charts, detailed maps, observing news, and information on events worldwide are carried in the Occultation Newsletter of the International Occultation Timing Association (IOTA). For local data about all events possibly visible from your location, send your longitude and latitude, $1.00, and a large, self-addressed envelope to Jim Hart, 2616 Monte Cresta, Belmont, CA 94002-1214, or obtain the information free by e-mail request.