The highlight of the June sky comes on the 21st when the sun creeps furthest north in the heavens and heralds the beginning of summer in the northern hemisphere -- the summer solstice. Solstice time this year is 7:45 a.m. EDT. Such is the kind of data that the U.S. Naval Observatory offers to skywatchers every month. Evening skygazers can set their sights in June on Mercury and Venus (the brighter of the two).Both can be seen low in the west just after sunset. Venus is visible till the end of the year, but Mercury will disappear June 14, when it moves into its "inferior conjunction" and comes between the earth and the sun. After the 21st, Mercury will be visible just before dawn. Other data: The moon is farthest from the earth -- its apogee -- at 11 p.m. June 13 (248,997 miles), closest -- its perigee -- at 10 a.m. June 1 (220,155 miles) and 3 p.m. June 29 (222,363 miles). If this whets your astronomical appetite, consider taking a day or night tour of the observatory. Nighttime visitors get to look through the observatory's telescopes, weather permitting. Night tours are booked through most of the summer, but it's never too early to reserve for October, one of the best months for stargazing.