Star Points for June, 2005; by Curtis Roelle This Month's Superior Conjunction of Inferior Planets This month holds a good viewing opportunity for users of binoculars or telescopes of any size. Venus and Mercury will appear very close together in the evening sky on Monday June 27 as Saturn hovers nearby. Mercury and Venus are the "inferior" planets. Inferior planets are those whose orbits around the sun lie within earth's orbit. Mercury and Venus are the only two planets that fit the description. An "appulse" of Mercury and Venus occurs during the afternoon of the 27th. Astronomer Guy Ottewell defines an appulse as "when two bodies are nearest (in apparent angular distance)." This means they appear close together in the sky although they may be far apart along the line of sight. Indeed, although they seem close together in the sky both planets are tens of millions of miles apart with Mercury lying between us and Venus. Mercury and Venus will both be on the opposite side of the sun at the time. But in the sky they're less than four arcminutes apart. This angular distance is the same as the width of a dime viewed at a distance of 53 feet. Although Venus and Mercury will both be above our horizon during the appulse it will be during daylight hours for us in the U.S. Although it is technically possible to view planets during the day a discussion of the technique for doing so is beyond the scope of this article. (If you are interested in trying it, check out the June issue of Sky & Telescope magazine available at the public library.) Several hours later the planets will be in conjunction. This simply means that they share the same Right Ascension or R.A. R.A. is a celestial coordinate analogous to Longitude used to measure the surface of the earth. Basically it means they lie exactly north and south of each other. The good news is that by the time it is getting dark the planets remain very close together. If you go out at 09:15 p.m. and look toward the west-northwest you should see the bright planet Venus about ten degrees above the horizon. For scale, the width of an outstretched fist is also approximately ten degrees. If you look at Venus with binoculars you will also see fainter Mercury to its lower left. Both should also fit within the same low power telescopic field of view. You may also notice Saturn located a short distance away to the lower right with binoculars or even with the naked eye. However, at 09:15 p.m. it is just seven degrees above the horizon. Saturn is just a little brighter than Mercury. Try finding a place with a low clear west-northwest horizon. As the sky darkens, all three planets will continue sinking closer to the horizon. Good luck with your observation. If you'd like to report your observation or have any questions don't hesitate to drop me an e- mail.