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July 2012 Celestial Calendar

Dave Mitsky

Note: All times in UTC (EST + 5)

Friedrich Bessel was born this month. The first photograph of a star, namely Vega, was taken on July 17, 1850. The first photograph of a total solar eclipse was taken on July 28, 1851.

The peak of the Southern Delta Aquarids occurs two days after First Quarter Moon this year.

The Moon is 11.4 days old and is located in Scorpius on July 1 at 0:00 UT. The Moon is at its greatest northern declination of +21.7 degrees on July 16 and its greatest southern declination of –21.7 degrees on July 2 and -21.6 degrees on July 29. Longitudinal libration is at a maximum of +6.6 degrees on July 7 and a minimum of -5.2 degrees on July 20. Latitudinal libration is at a maximum of +6.6 degrees on July 21 and a minimum of -6.8 degrees on July 7. Visit http://saberdoesthestars.wordpress.com/2011/07/05/saber-does-the-stars/ for tips on spotting extreme crescent Moons. Times and dates for the lunar light rays predicted to occur in June are available at http://www.lunar-occultations.com/rlo/rays/rays.htm

The Sun is located in Gemini on July 1. The Earth is farthest from the Sun on July 5, when it is 3.3% more distant than it was at perihelion.

Brightness, apparent size, illumination, distance from the Earth in astronomical units, and location data for the planets and Pluto on July 1: Mercury (+0.4 magnitude, 8.1", 41% illuminated, 0.83 a.u., Cancer), Venus (-4.6 magnitude, 44.7", 16% illuminated, 0.37 a.u., Taurus), Mars (+0.9 magnitude, 6.6", 89% illuminated, 1.42 a.u., Virgo), Jupiter (-2.0 magnitude, 34.0", 100% illuminated, 5.81 a.u., Taurus), Saturn (+0.7 magnitude, 17.6", 100% illuminated, 9.46 a.u., Virgo), Uranus (+5.8 magnitude, 3.6", 100% illuminated, 20.02 a.u., Cetus), Neptune (+7.8 magnitude, 2.3", 100% illuminated, 29.38 a.u., Aquarius), and Pluto (+14.0 magnitude, 0.1", 100% illuminated, 31.24 a.u., Sagittarius).

Mercury is located in the west, Mars in the southwest, and Saturn in the southeast during the evening. At midnight, Saturn is in the west, Uranus in the east, and Neptune in the southeast. In the morning, Venus and Jupiter can be found in east, Uranus in the southeast, and Neptune in the south.

At midmonth, Mercury is visible during evening twilight, Venus rises at 3:00 a.m., Mars sets at midnight, Jupiter rises at 3:00 a.m., and Saturn sets at 1:00 a.m. local daylight time for observers at latitude 40 degrees north.

Mercury is at greatest eastern elongation and at the descending node on evening of June 30 (July 1 in UT) and at aphelion on July 12. The speedy planet fades in brightness and appears lower in the sky each night as July progresses. Mercury reaches inferior conjunction on July 28.

Venus attains greatest brilliancy (magnitude -4.7) on July 12, when it appears as a 27%-illuminated waxing crescent. Venus and Jupiter are only 4.8 degrees apart and are in quasi-conjunction on the morning of July 1. At that time, Venus is situated in the Hyades, 2.5 degrees from Aldebaran, Jupiter is 5 degrees above Venus, and M45 (the Pleiades) is 6 degrees above Jupiter. By month's end, the two planets are separated by 14 degrees.

A faint and tiny Mars passes south of the celestial equator on July 5 and is at the descending node on the ecliptic on July 24. Mars and Saturn begin the month 24 degrees apart but are only 8 degrees from one another by the end of July.

Jupiter increases in apparent size from 34 to 36 arc seconds and brightens by two-tenths of a magnitude during July. Jupiter is occulted by a waning crescent Moon on July 15 for most of Europe and parts of Asia. Click on http://www.skyandtelescope.com/observing/objects/planets/3304091.html?page=1&c=y to determine transit times of the central meridian by the Great Red Spot. Data on the Galilean satellites is available at http://www.skyandtelescope.com/observing/objects/javascript/3307071.html

Saturn is at eastern quadrature on July 15. The tilt angle of Saturn's rings is 13 degrees this month. Eighth-magnitude Titan is north of the planet on July 15 and July 31 and south of it on July 7 and July 23. Saturn's odd moon Iapetus is positioned 2.5 arc minutes north-northwest of Saturn and shines at eleventh-magnitude on July 31. Titan is just 0.7 arc minute north of Saturn on that date. For further information on Saturn's satellites, browse http://www.skyandtelescope.com/observing/objects/javascript/3308506.html

Uranus is located less than two degrees east-northeast of the sixth-magnitude star 44 Piscium for the entire month. It is stationary on July 13 and then begins to retrograde, moving westward with respect to the fixed stars. This change in apparent motion is due to Uranus being overtaken by the faster-moving Earth.

Neptune can be found less than two degrees north of the fifth-magnitude star 42 Aquarii.

Finder charts for Uranus and Neptune can be found at http://media.skyandtelescope.com/documents/Uranus-Neptune-2012.pdf

Pluto reached opposition late last month and is well-placed for observing during the middle of the night. A detailed finder chart is available on pages 52 and 53 of the June issue of Sky & Telescope.

For more on the planets and how to locate them, browse http://www.nakedeyeplanets.com/

The periodic comet 96P/Machholz reaches perihelion on July 14. It may be visible low in the northwest by July 21. As it heads eastward from Leo Minor into Leo, Comet 96P/Machholz may attain a brightness of seventh magnitude before fading rapidly to tenth magnitude by the end of month. Browse http://cometchasing.skyhound.com/ and http://www.aerith.net/comet/future-n.html for additional information on comets visible in July.

Asteroid 18 Melpomene travels through Serpens Cauda and Ophiuchus this month. From July 5 to July 11, the tenth-magnitude asteroid is located less than one degree from the third-magnitude star Nu Ophiuchi. A finder chart appears on page 52 of the July issue of Sky & Telescope. Data on asteroid occultations taking place in July is available at http://www.asteroidoccultation.com/2012_07_si.htm

A free star map for July can be downloaded at http://www.skymaps.com/downloads.html

The Mira-type variable star R Draconis is predicted to be at maximum on July 12. For further information, see the article on pages 50 and 51 of the July issue of Sky & Telescope.

Binary and Multiple Stars for July

Eta Draconis, 17 & 16 Draconis, Mu Draconis, Struve 2273, Nu-1 & Nu-2 Draconis, Psi Draconis (Draco); Kappa Herculis, Gamma Herculis, Struve 2063, 56 Herculis, Struve 2120, Alpha Herculis (Ras Algethi), Delta Herculis, Rho Herculis, Mu Herculis (Hercules); Rho Ophiuchi, Lambda Ophiuchi, 36 Ophiuchi, Omicron Ophiuchi, Burnham 126 (ADS 10405), Struve 2166, 53 Ophiuchi, 61 Ophiuchi (Ophiuchus); h5003 (Sagittarius); Xi Scorpii, Struve 1999, Beta Scorpii, Nu Scorpii, 12 Scorpii, Sigma Scorpii, Alpha Scorpii (Antares), h4926 (Scorpius); Struve 2007, 49 Serpentis, Struve 2031 (Serpens Caput); 53 Serpentis, Struve 2204, h4995, h2814 (Serpens Cauda); Epsilon Ursae Minoris (Ursa Minor)

Notable carbon star for July: T Draconis

Top ten binocular deep-sky objects for July: IC 4665, LDN 1773, M4, M6, M7, M10, M12, M13, M92, NGC 6231

Top ten deep-sky objects for July: M4, M6, M7, M10, M12, M13, M92, NGC 6210, NGC 6231, NGC 6543

Challenge deep-sky object for July: NGC 6380 (Scorpius)

The objects listed above are located between 16:00 and 18:00 hours of right ascension.