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July 2010 Celestial Calendar

Dave Mitsky

Note: All times in UTC (EST + 5)

The Southern Delta Aquarids are compromised by a gibbous Moon this year.

The Moon is 18.5 days old and is located in Aquarius on July 1 at 0:00 UT. See http://www.lunar-occultations.com/iota/iotandx.htm for further information. The Moon is at its greatest northern declination of +25.0 degrees on July 9 and its greatest southern declination of -25.0 degrees on July 22. Longitudinal libration is at a maximum of +6.7 degrees on July 20 and a minimum of -6.6 degrees on July 7. Latitudinal libration is at a maximum of +6.9 degrees on July 17 and a minimum of -6.9 degrees on July 4 and -6.8 degrees on July 31. Visit http://www.astronomyblogs.com/member/saberscorpx/?xjMsgID=50821 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 6, when it is 3.3% more distant than it was at perihelion. A total solar eclipse occurs in the South Pacific and southern Chile and Argentina on July 11. Maximum totality is 5 minutes 20 seconds long and occurs between Tahiti and Easter Island at 19:33:31 UT. For further information, see http://eclipse.gsfc.nasa.gov/SEmono/TSE2010/TSE2010.html

Brightness, apparent size, illumination, distance from the Earth in astronomical units, and location data for the planets and Pluto on July 1: Mercury (-2.0 magnitude, 5.1", 99% illuminated, 1.33 a.u., Gemini), Venus (-4.1 magnitude, 15.5", 71% illuminated, 1.08 a.u., Leo), Mars (1.3 magnitude, 5.2", 91% illuminated, 1.79 a.u., Leo), Jupiter (-2.5 magnitude, 41.5", 99% illuminated, 4.75 a.u., Pisces), Saturn (1.1 magnitude, 17.2", 100% illuminated, 9.66 a.u., Virgo), Uranus (5.8 magnitude, 3.6", 100% illuminated, 19.92 a.u., Pisces), Neptune (7.8 magnitude, 2.3", 100% illuminated, 29.35 a.u., Aquarius), and Pluto (14.0 magnitude, 0.1", 100% illuminated, 30.85 a.u., Sagittarius).

On July evenings, Mercury, Venus, Mars, and Saturn are located in the west. At midnight, Jupiter and Uranus are in the east. In the morning, Jupiter and Uranus can be seen in the south.

At midmonth, Mercury is visible during evening twilight, Venus sets at 11:00 p.m. EDT, Mars sets at 11:00 p.m. EDT, Jupiter rises at midnight, and Saturn sets at midnight for observers at latitude 40 degrees north.

Two conjunctions occur this month: Venus and Regulus on July 10 and Mercury and Regulus on July 27. The distance between Venus and Saturn drops from 38 degrees on July 1 to less than eight degrees on July 31. At the start of July, Mars and Saturn are separated by 15 degrees. Venus, Saturn, and Mars form an acute triangle on July 31. The gap between Mars and Saturn is less than two degrees that night.

Mercury is visible very close to the western horizon during the final two weeks of July. (It's highest on July 26 for observers at our latitude of 40 degrees north.) Mercury fades from magnitude -0.5 to magnitude 0.1 during this period.

Venus shines brilliantly this month, reaching magnitude -4.3 by month's end. As Venus approaches the Earth, it increases in apparent size from 15.5 to 19.7 arc seconds and decreases in illuminated extent from 71 to 59%.

Mars leaves Leo and enters Virgo on July 19. The Red Planet subtends less than five arc seconds by the end of the month and is no longer a viable telescopic target.

Jupiter rises at approximately 10:30 p.m. EDT by the end of July. The gas giant is north of the celestial equator from July 8 to July 30. Jupiter increases in apparent size from 41.5 to 45.6 arc seconds and brightens by two-tenths of a magnitude during July. Io, the closest of Jupiter's Galilean satellites, is eclipsed by Jupiter on July 6 at 5:04 a.m. EDT. An Io shadow transit begins the following night at 2:13 a.m. EDT, followed by a transit of the moon at 3:34 a.m. EDT. On the nights of July 5, July 8, and July 18, all four of the Galilean satellites lie to one side of Jupiter. Click on http://skyandtelescope.com/observing/objects/planets/article_107_1.asp to determine transit times of the central meridian by the Great Red Spot. Data on the Galilean satellites is available at http://skytonight.com/observing/objects/javascript/3307071.html

Saturn's rings are inclined 3 degrees with respect to the Earth in July. Saturn's moons Dione and Rhea are separated by one arc minute on July 11 and three arc minutes on July 17. Titan, Dione, and Rhea pass within 30 arc minutes of each other on July 27. On July 28, Enceladus and Tethys are ten arc minutes apart. Titan and Dione are separated by the same distance on the opposite side of Saturn's rings that night. For further information on Saturn's satellites, browse http://skytonight.com/observing/objects/javascript/3308506.html

Due to the eastward motion of Jupiter, Uranus decreases in distance from two to three degrees west of Jupiter during the course of the month. Uranus begins retrograde motion on July 6.

Neptune can be seen in the pre-dawn hours. It attains an altitude of approximately 20 degrees in the southeast by midnight and is bright enough to be seen with binoculars.

Finder charts for Uranus and Neptune are posted at http://media.skyandtelescope.com/documents/Uranus_Neptune_2010.pdf

Pluto reached opposition late last month and is well placed during the middle of the night. A finder chart is available on page 60 of the July 2010 issue of Sky & Telescope and online at http://www.skyandtelescope.com/skytel/beyondthepage/89002802.html

The periodic comet 10P/Tempel shines at eighth-magnitude as it travels eastward through Cetus this month. It reaches perihelion on July 4. Comet C/2009 R1 (McNaught) reaches perihelion on July 2 and may be visible very low in the western sky in Cancer for a few minutes after sunset. This comet may be the brightest of the year. Browse http://cometchasing.skyhound.com and http://www.aerith.net/comet/future-n.html for additional information on these and other comets visible in July.

During July, asteroid 1 Ceres glides southwestward through Ophiuchus. The dwarf planet shines at seventh-magnitude as it passes to the south of the third-magnitude star Theta Ophiuchi and through the dark nebula known as the Pipe Nebula (LDN 1773). Ceres is just north of a sixth-magnitude binary star on the night of July 6.

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

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)

Challenge binary star for July: 24 Ophiuchi

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

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

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