Sky chart for July: watch Venus while you can; Northern Hemisphere gazer's guide
All month: July offers the last good opportunities to see Venus as an evening star this time around. The planet was probably at its best in May, when it was more favorably placed relative to the sun, although it is still near its greatest distance to the sun's left in early July and is at maximum brilliancy on the 19th. Toward the end of July, the brilliant planet is fading and its distance from the sun is decreasing rapidly as Venus's conjunction with the sun approaches in late August. You will probaby still be able to see it in early August, but very low in the west late in evening twilight.
Jupiter and Saturn, with Antares and Spica as companion stars, still continue to put on a good show in the evening, getting better if anything as their easterly elongations from the sun decrease and they become more discernible in the western sky after sundown. Early in July, they are high in the south as twilight ends, more to the south-southwest late in the month. Jupiter is by far the brighter, with ruddy Antares below to its left. Saturn and nearby Spica are nearly identical in brightness, Saturn higher and to the left of the star. Both planets end their retrograde motion in July, Saturn at the beginning and Jupiter at the end of the month, turning then toward the east (left) again. This separates Saturn from Spica, but brings Jupiter closer to Antares.
Mars and Mercury are both near the sun and not well placed in July, Mars a morning star, Mercury moving from the morning to the evening sky early in the month.
July 1: The month begins with a morning moon, waning gibbous, two days before last quarter, rising shortly before midnight and remaining in the sky almost till noon, just south of the vernal equinox near the southern border of the constellation Pisces.
July 2: Saturn has been drifting to the right relative to the stars since mid-February, its retrograde motion taking it closer to Spica, the bright star of Virgo. But this westerly drift ends today; Saturn becomes momentarily stationary (in celestial longitude) and then resumes its normal easterly movement, taking it away from Spica again. In 1982, this shifting of Saturn's direction took it past Spica three times (a ''triple'' conjunction), but this is not the case this year.
July 3: Last quarter moon occurs today, still near the southern border of Pisces. Look for it in the western sky as a daytime object this morning, in the eastern sky well after midnight tonight after it rises again.
July 6: Earth is at aphelion, the position in its orbit most distant from the sun (152,103,000 kilometers, or 94,512,000 miles away). Today, the sun is technically smallest in our sky, its tidal force on Earth is weakest, and the least of its energy (including heat) reaches Earth. You wouldn't ordinarily realize that from the weather we experience in the Northern Hemisphere, of course, but that's because our seasons are not dependent on the sun's distance, though it is one factor that affects their relative severity.
July 8: This may be the last morning you will see the waning crescent moon during this cycle of phases, rising this morning about two hours before the sun. A pretty sight in the dawn sky, the moon is near Aldebaran, the ruddy bright star of Taurus, to its right. Perhaps you remember Aldebaran as a winter star. It is, as an evening object, but now, of course, it is a morning star, to the sun's right. Give it time, however. As the sun shifts east (left) relative to it , Aldebaran gradually rises earlier with each passing day until, by next winter, it is well up in the early evening.
July 9: Mercury is in superior conjunction today, in line with, but beyond the sun. Moving from right to left past the sun, it now enters the evening sky. It improves gradually as an evening star over the next month or so, but it isn't very good even at its best. Venus passes the star Regulus tonight. Remember how far to the planet's left the star was last month? Now Venus moves to its left and slowly away from it. The planet is closest below Regulus (conjunction) about 6 p.m. Eastern standard time (EST).
July 10-11: New moon is at 7:18 a.m. on July 10, in Gemini. In Cancer on the 11th, the moon is at perigee (nearest Earth) at about 5 a.m., some 22 hours after it is new. The combined effect of syzygy (Earth-moon-sun in line) and perigee will make for strong tides Tuesday morning and night.
July 12-13: You may see the early crescent moon on the 12th; you should surely see it on the 13th, both nights in the west after sundown. The moon passes well above Venus on the morning of the 13th, shifting from right to left past the bright planet between the two evenings.
July 14: The crescent moon is in Virgo tonight, just north of where the autumnal equinox is located. The bright objects higher to its left are Saturn (above) and the star Spica, with much brighter Jupiter still farther left.
July 16: First quarter moon is very close to Saturn tonight, while Spica is to their right and lower. The moon passes above Saturn (conjunction) about 4 a.m. EST on the 17th.
July 17-18: The waxing gibbous moon is in Libra both evenings, between Saturn (to its right) and Jupiter (to its left), closer to Saturn on the 17th, to Jupiter on the 18th.
July 19: You won't notice the difference, but Venus reaches its greatest brilliancy as an evening star today. The planet is easily visible low in the southwest at dusk, and it is noticeably brighter than it was, say, three or four months ago, when it first became obvious as an evening object. However, even though now at its brightest, it is well past its best elongation from the sun and hence not nearly so well placed for viewing, appearing in the twilight lower and setting earlier. Its future as an evening star this year is now limited to a few weeks. The moon passes from right to left above Jupiter at about 11 p.m. EST , and its motion relative to the planet will be easy to follow as it approaches, then draws away while both drift westward together.
July 20: The stars of Scorpius can be seen readily below Jupiter this month, curving down to the left past its bright reddish Antares and then bending in a sharp ''hook'' up to the right. Seamen often refer to the constellation as a gancho, Spanish for stevedore's hook. Find Antares easily by looking midway between the moon and Jupiter, then downward.
July 22: Early this evening, the bright moon, two days before full, is in Sagittarius, almost directly at the peak of the Teapot's cover.
July 24: Full moon is at 6:27 p.m. EST, and the moon rises at sundown just inside the eastern border of Capricornus.
July 26: The moon is at apogee this morning, and this evening it has slipped over the border into Aquarius. Scattered moonlight so greatly brightens the sky tonight (and has for the past several nights that the moon has spent in Capricornus) as to make the dim stars of the ''sea goat'' virtually impossible to see.
July 29: Jupiter becomes stationary among the stars, ending its retrograde (westerly) motion and returning to its normal (easterly) movement. The moon returns tonight virtually to the same position in which you saw it on July 1, at the southern border of the constellation Pisces just below the position of the vernal equinox. You should easily find the square of Pegasus above the moon (in line with the two stars on the left side of the square) and the brighter star Diphda below it. They help mark the location of the vernal equinox, the origin from which astronomers measure the east-west positions of stars (sort of like a Greenwich Observatory among the stars).
July 31: At month's end, the waning gibbous moon is still in Pisces, now a morning object, rising close to 11 p.m. and remaining in the sky past sunrise through most of the morning.