August Celestial Calendar by Dave Mitsky
All times, unless otherwise noted, are UT (subtract four hours and, when appropriate, one calendar day for EDT)
8/1 The astronomical cross-quarter day known as Lammas or Lughnasadh occurs today; Venus is at the descending node through the ecliptic plane at 17:00; asteroid 4 Vesta is stationary at 23:00
8/2 A double Galilean satellite shadow transit begins at 20:18
8/4 The Moon is 4.7 degrees south-southeast of Uranus at 1:00; Last Quarter Moon occurs at 18:18; the Moon is 1.2 degrees north of asteroid 3 Juno, with an occultation occurring in far northern Canada, northeastern Greenland, Scandinavia, western Russia, and eastern Europa, at 23:00
8/5 The Curtiss Cross, an X-shaped clair-obscur illumination effect located between the craters Parry and Gambart, is predicted to be visible at 7:34
8/6 Venus crosses the celestial equator and enters the southern hemisphere at 2:00; the Moon is 8.9 degrees south-southeast of the bright open cluster M45 (the Pleiades or Subaru) at 3:00; a double Galilean satellite shadow transit begins at 9:16; the Moon is 1.1 degrees north of the first-magnitude star Aldebaran (Alpha Tauri), with an occultation occurring in far northern Canada, most of Greenland, Svalbard, central Russia, and Mongolia, at 19:00; Jupiter is at eastern quadrature at 23:00
8/7 Asteroid 2 Pallas is in conjunction with the Sun at 13:00; Uranus is stationary in right ascension, with retrograde (western) motion to begin, at 21:00
8/8 The Moon is 3.8 degrees south of the bright open cluster M35 in Gemini at 8:00
8/9 Mercury is in inferior conjunction (0.604 astronomical unit from the Earth and 4.8 degrees south of the Sun) at 2:00; Mercury is at greatest latitude south of the ecliptic plane (-7.0 degrees) at 16:00; the Moon is 7.8 degrees south of the first-magnitude star Pollux (Beta Geminorum) at 19:00; a double Galilean satellite shadow transit begins at 22:13
8/10 The Moon is at the ascending node (longitude 125.9 degrees) at 13:42; the Moon displays minimum libration for the year (0.08 degree) at 14:00; the Moon is 1.1 degrees south of the bright open cluster M44 (the Beehive Cluster or Praesepe) in Cancer at 17:00; the Moon is at perigee, subtending 33' 22'' from a distance of 358,078 kilometers (222,500 miles), at 18:07; the Sun enters Leo (at longitude 138.18 degrees on the ecliptic) at 21:00
8/11 The Moon is 5.4 degrees north-northeast of Mercury at 3:00; a partial solar eclipse visible from northeastern Canada, Greenland, Iceland, northern Europe, most of Russia, and northeastern Asia begins at 8:02; New Moon (lunation 1183) occurs at 9:58
8/12 The Moon is 1.7 degrees north-northeast of the first-magnitude star Regulus (Alpha Leonis) at 4:00
8/13 The peak of the Perseid meteor shower (a zenithal hourly rate of 150 or more per hour) occurs at 1:00; a double Galilean satellite shadow transit begins at 11:10
8/14 The Moon is 5.9 degrees north-northeast of Venus at 18:00
8/15 Venus is at theoretical dichotomy (50% illuminated as seen from Earth) at 5:00; the Moon is 7.2 degrees north-northeast of the first-magnitude star Spica (Alpha Virginis) at 22:00
8/16 Mars is at greatest declination south (-26.5 degrees) at 12:00; the Moon is at maximum libration (10.2 degrees) for the year
8/17 A double Galilean satellite shadow transit begins at 0:08; the Moon is 4.3 degrees north-northeast of Jupiter at 13:00; Venus is at greatest eastern elongation (45.9 degrees) at 17:00
8/18 First Quarter Moon occurs at 7:49; Mercury is stationary in right ascension, with direct or prograde (eastern) motion to begin, at 12:00; the Lunar X, also known as the Werner or Purbach Cross, an X-shaped clair-obscur illumination effect involving various ridges and crater rims located between the craters La Caille, Blanchinus, and Purbach, is predicted to begin at 18:05; sunrise takes place at the isolated lunar mountain Mons Pico at 22:46
8/19 Mercury is stationary in longitude at 4:00; the Moon is 8.9 degrees north of the first-magnitude star Antares (Alpha Scorpii) at 13:00; sunrise takes place at the isolated lunar mountain Mons Piton at 13:53
8/20 A double Galilean satellite shadow transit begins at 13:16
8/21 Mars is at its greatest latitude south of the ecliptic plane (-1.8 degrees) at 2:00; Mercury (magnitude +1.1) is 5.4 degrees southeast of M44 at 3:00; the Moon is 2.1 degrees north of Saturn at 10:00
8/22 A double Galilean satellite shadow transit begins at 8:50
8/23 The Moon is at apogee, subtending 29' 27'' from a distance of 405,746 kilometers (252,119 miles), at 11:23; the Moon is 6.7 degrees north of Mars at 16:00
8/24 A double Galilean satellite shadow transit begins at 2:35; the Moon is at the descending node (longitude 305.9 degrees) at 4:52
8/26 Full Moon (known as the Fruit, Grain, Green Corn, or Sturgeon Moon) occurs at 11:56; Mercury is at greatest western elongation (18.0 degrees) at 21:00
8/27 The Moon is 2.3 degrees south-southeast of Neptune at 12:00; Mars is stationary in longitude at 14:00; a double Galilean satellite shadow transit begins at 15:54
8/28 Mars is stationary in right ascension, with direct or prograde (eastward) motion to resume, at 10:00; Mercury is at the ascending node through the ecliptic plane at 17:00
8/31 A double Galilean satellite shadow transit begins at 5:12; the Moon is 4.6 degrees south-southeast of Uranus at 6:00
John Flamsteed, Christian Mayer, Pierre François André Méchain, Maria Mitchell, and Otto Struve were born this month.
The gibbous phase of Mars was first observed by Francesco Fontana on August 24, 1638. Abraham Ihle discovered the globular cluster M22 on August 26, 1665. Nicolas Sarabat discovered Comet C/1729 P1 (Sarabat) on August 1, 1729. Caroline Herschel discovered Comet C/1786 P1 (Herschel) on August 1, 1786. The Saturnian satellite Enceladus was discovered by William Herschel on August 28, 1789. Dominique Dumouchel was the first person to observe the return of Comet 1P/Halley on August 5, 1835. John Russell Hind discovered asteroid 7 Iris on August 13, 1847. Asaph Hall discovered Deimos on August 11, 1877 and Phobos on August 17, 1877. The first extragalactic supernova, S Andromedae, was discovered by Ernst Hartwig on August 20, 1885. David Jewitt and Jane Luu discovered the trans-Neptunian object (15760) 1992 QB1 on August 30, 1992.
The peak of the Perseid meteor shower takes place on the night of August 12th/August 13th and is not affected by moonlight. Comet 109P/Swift-Tuttle is the source of Perseid meteors. The shower’s radiant is just to the southeast of the Double Cluster (NGC 869 and NGC 884). For more on this year’s Perseids, see pages 48 and 49 of the August 2018 issue of Sky & Telescope or click on http://www.timeandda...er/perseid.html and http://earthsky.org/...d-meteor-shower
Information on Iridium flares and passes of the ISS, the Tiangong-2, the USAF’s X-37B, the HST, and other satellites can be found at http://www.heavens-above.com/
The Moon is 18.7 days old, is illuminated 86%, subtends 29.8 arc minutes, and is located in Aquarius on August 1st at 0:00 UT. The Moon is at its greatest northern declination on August 9th (+20.7 degrees) and its greatest southern declination on August 22nd (-20.7 degrees). Longitudinal libration is at a maximum of +7.6 degrees on August 17th and a minimum of -7.0 degrees on August 3rd. Latitudinal libration is at a maximum of +6.8 degrees on August 5th and a minimum of -6.8 degrees on August 17th. The Moon is at perigee (at a distance of 56.14 Earth-radii) on August 10th and at apogee (at a distance of 63.62 Earth-radii) on August 23rd. New Moon (i.e., the dark of the Moon) occurs on August 11th. Large tides will take place following New Moon. The Moon occults asteroid 3 Juno on August 4th and Aldebaran on August 6th from certain parts of the world. Browse http://www.lunar-occ...bstar/bstar.htm for information on upcoming lunar occultations. Visit http://saberdoesthes...does-the-stars/ for tips on spotting extreme crescent Moons. Click on https://www.calendar...dar/2018/august for a lunar phase calendar for this month. Times and dates for the lunar crater light rays predicted to occur in August are available at http://www.lunar-occ.../rays/rays.htm
The Sun is located in Cancer on August 1st. It enters the constellation of Leo on August 10th. A partial solar eclipse, the sixth member of Saros 155 and the last eclipse of the year, takes place in northeastern Canada, Greenland, Iceland, northern Europe, most of Russia, and northeastern Asia on August 11th. Greatest eclipse occurs at 9:46:19 UT1. For further information on this eclipse, consult http://eclipsewise.c...ml#SE2018Aug11P
Brightness, apparent size, illumination, distance from the Earth in astronomical units, and location data for the planets and Pluto on August 1: Mercury (magnitude +2.9,11.0", 8% illuminated, 0.61 a.u., Leo), Venus (magnitude -4.3, 20.4", 57% illuminated, 0.82 a.u., Leo), Mars (magnitude -2.8., 24.3", 100% illuminated, 0.39 a.u., Capricornus), Jupiter (magnitude -2.1, 37.9", 99% illuminated, 5.20 a.u., Libra), Saturn (magnitude +0.2, 18.0", 100% illuminated, 9.22 a.u., Sagittarius), Uranus (magnitude +5.8, 3.6", 100% illuminated, 19.50 a.u. on August 16th, Aries), Neptune (magnitude +7.8, 2.4", 100% illuminated, 29.00 a.u. on August 16th, Aquarius), and Pluto (magnitude +14.2, 0.1", 100% illuminated, 32.78 a.u. on August 16th, Sagittarius).
This month Venus is visible in the west, Mars in the southeast, Jupiter in the southwest, Saturn in the south, and Neptune in the east during the evening. At midnight, Mars can be found in the south, Saturn in the southwest, Uranus in the east, and Neptune in the southeast. In the morning, Mercury is in the east, Uranus is in the south, and Neptune is in the southwest.
Mercury reaches its greatest heliocentric latitude south and is inferior conjunction on August 9th. The speediest planet is stationary on August 18th, reaches a greatest western elongation of 18 degrees on August 26th, and is at the ascending node on August 28th. Mercury reappears in the morning sky in late August. This will be the best morning apparition of the planet in 2018.
Venus changes in phase from gibbous to crescent this month. It’s at the descending node on August 1st. The waxing crescent Moon passes six degrees north of Venus on August 14th. The brightest planet reaches a greatest eastern elongation of 46 degrees and has decreased in declination by 18 degrees on August 17th. On August 31st, Venus shines at magnitude -4.6, is illuminated 41%, and subtends 28.8 arc seconds. By that date, the sunset altitude of the planet has decreased to approximately 15 degrees.
During August, Mars decreases in angular size from 24.3 arc seconds to 21.0 arc seconds and in brightness from magnitude -2.8 to magnitude -2.1. The planet’s retrograde (western) motion carries Mars into Sagittarius on August 24th. At a declination of -26 degrees, the Red Planet is low in the sky for northern observers. On August 21st, Mars reaches its greatest heliocentric latitude south. The waxing gibbous Moon passes seven degrees north of Mars on August 23rd. Mars reaches its second stationary point on August 28th, after which it begins prograde (eastward) motion once again. If the current dust storm abates, observers in North America may be able to see Aurorae Sinus on the central meridian in early August, Sinus Meridiani on August 9th and August 10th, Syrtis Major and Hellas from August 16th to August 18th, and Mare Sirenum on August 30 and August 31st. Martian surface feature simulators are available at https://is.gd/marsprofiler and https://www.calsky.c...gi/Planets/5/1?
Jupiter sets around 10:30 p.m. local daylight time by the end of the month. It drops in brightness from magnitude -2.1 to magnitude -1.9 and decreases in angular diameter from 37.9 to 34.9 arc seconds during August. Jupiter reaches eastern quadrature on August 6th. At mid-month, the gas giant is situated approximately half a degree north of the second-magnitude binary star Zubenelgenubi (Alpha Librae). The nearly First Quarter Moon passes five degrees north of Jupiter on August 17th. Double Galilean satellite shadow transits occur on August 2nd, August 6th, August 9th, August 13th, August 15th, August 17th, August 20th, August 22nd, August 24th, August 27th, and August 31st. Information on Great Red Spot transit times and Galilean satellite events is available on pages 50 and 51 of the August 2018 issue of Sky & Telescope and online at http://www.skyandtel...watching-tools/ and https://www.projectp...m/jevent.htm
Saturn is visible at dusk and sets after midnight. Saturn’s retrograde motion through northwestern Sagittarius slows in August. The Ringed Planet lies 2.7 degrees east of M20 (the Trifid Nebula) as the month begins and is approximately 1.7 degrees distant from M20 by the end of August. Saturn is 17.7 arc seconds in angular diameter at its equator on August 15th. Its ring system spans 40 arc seconds and is inclined more than 26 degrees with respect to the Earth. The waxing gibbous Moon passes two degrees to the north of Saturn on August 21st. On August 8th, the peculiar satellite Iapetus lies 1.7 arc minutes south of Saturn and shines at eleventh magnitude. Iapetus is 8.8 arc minutes from Saturn when it reaches greatest western elongation on August 28th. For additional information on Saturn’s satellites, browse http://www.skyandtel...atching-tools/
Uranus lies twelve degrees south of the second-magnitude star Hamal (Alpha Arietis) this month. Three sixth-magnitude stars are situated within two degrees of the ice giant. On the night of August 3rd/4th, the waning gibbous Moon passes five degrees south of Uranus. The waning gibbous Moon passes five degrees south of the planet once again on the night of August 30th/August 31st. Uranus is stationary in right ascension and begins retrograde (westward) motion on August 7th. Browse http://www.bluewater...anus_2018_1.pdf for a finder chart.
Neptune is located 1.4 degrees west-southwest of the fourth-magnitude star Phi Aquarii on the first day of August. The waning gibbous Moon passes two degrees to the south of Neptune on August 27th. A finder chart is posted http://www.bluewater...ne_2018_1.pdf
Additional online finder charts for Uranus and Neptune can be found at http://www.nakedeyep....com/uranus.htm and http://www.nakedeyep...com/neptune.htm and also at https://www.skyandte...WEB_UrNep18.pdf
Pluto is located below the Teaspoon asterism in northeastern Sagittarius at a declination of nearly -22 degrees. The dwarf planet is highest in altitude in the late evening. With each passing year, Pluto is growing fainter and getting lower in the sky as it moves southward. Finder charts for Pluto are available on pages 48 and 49 of the July 2018 issue of Sky & Telescope and page 243 of the RASC Observer’s Handbook 2018. A finder chart is posted online at http://www.bluewater...018-Mar2019.jpg
For more on the planets and how to locate them, see http://www.nakedeyeplanets.com/
Comet 21P/Giacobini-Zinner heads southeast from Cassiopeia into Camelopardalis. From August 15th to August 18th, the periodic comet passes through the region of IC 1805 (the Heart Nebula) and IC 1848 (the Soul Nebula). It comes within four degrees of the open cluster NGC 1502 on the night of August 22nd. Comet 21P has a period of 6.6 years and may attain a brightness of ninth magnitude this month. A short article on this comet can be found on page 50 of the August 2018 issue of Sky & Telescope. For further information on comets visible this month, browse http://cometchasing.skyhound.com/ and http://www.aerith.ne.../future-n.html
Asteroid 4 Vesta shines at seventh magnitude this month as it travels southwestward through southern Ophiuchus. The main belt asteroid passes less than ten arc minutes south of the fifth-magnitude star 51 Ophiuchi on the evenings of August 20th and August 21st. Asteroids brighter than magnitude +11.0 that reach opposition this month include 70 Panopaea on August 10th and 230 Athamantis on August 26th. For information on asteroid occultations taking place this month, see http://www.asteroido.../2018_08_si.htm
Various events taking place within our solar system are discussed at http://www.bluewater...ed-4/index.html
Data on current supernovae can be found at http://www.rochester...y.org/snimages/
Information pertaining to observing some of the more prominent Messier galaxies can be found at http://www.cloudynig...ur-astronomers/
Author Phil Harrington offers an excellent freeware planetarium program for binocular observers known as TUBA (Touring the Universe through Binoculars Atlas), which also includes information on purchasing binoculars, at http://www.philharrington.net/tuba.htm
Sixty binary and multiple stars for August: 5 Aquilae, Struve 2404, 11 Aquilae, Struve 2426, 15 Aquilae, Struve 2449, 23 Aquilae, Struve 2532, Pi Aquilae, 57 Aquilae (Aquila); Beta Cygni (Albireo), 16 Cygni, Delta Cygni, 17 Cygni (Cygnus); 41 & 40 Draconis, 39 Draconis, Struve 2348, Sigma Draconis, Struve 2573, Epsilon Draconis (Draco); 95 Herculis, 100 Herculis, Struve 2289, Struve 2411 (Hercules); Struve 2349, Struve 2372, Epsilon-1 & Epsilon-2 Lyrae (the Double-Double), Zeta-2 Lyrae, Beta Lyrae, Otto Struve 525, Struve 2470 & Struve 2474 (the Other Double-Double) (Lyra); 67 Ophiuchi, 69 Ophiuchi, 70 Ophiuchi, Struve 2276, 74 Ophiuchi (Ophiuchus); Mu Sagittarii, Eta Sagittarii, 21 Sagittarii, Zeta Sagittarii, H N 119, 52 Sagittarii, 54 Sagittarii (Sagittarius); Struve 2306, Delta Scuti, Struve 2373 (Scutum); Struve 2296, Struve 2303, 59 Serpentis, Theta Serpentis (Serpens Cauda); Struve 2445, Struve 2455, Struve 2457, 4 Vupeculae, Struve 2521, Struve 2523, Struve 2540, Struve 2586, Otto Struve 388, Struve 2599 (Vulpecula)
Notable carbon star for August: V Aquilae
Eighty deep-sky objects for August: B139, B142, B143, NGC 6709, NGC 6738, NGC 6741, NGC 6751, NGC 6755, NGC 6772, NGC 6778, NGC 6781, NGC 6804, PK64+5.1 (Aquila); NGC 6819, NGC 6826, NGC 6834, (Cygnus); NGC 6643, NGC 6742 (Draco); DoDz 9 (Hercules); M56, M57, NGC 6703, NGC 6791, Ste1 (Lyra); NGC 6572, NGC 6633 (Ophiuchus); H20, M71 (Sagitta); B86, B87, B90, B92, B93, M8, M17, M18, M20, M21, M22, M23, M24, M25, M28, M54, M55, M69, M70, M75, NGC 6520, NGC 6544, NGC 6546, NGC 6553, NGC 6565, NGC 6603, NGC 6818, NGC 6822 (Sagittarius); IC 4703, IC 4756, M16, NGC 6604 (Serpens Cauda); B100, B101, B103, B104, B110, B111, B113, Bas 1, IC 1295, M11, M26, NGC 6649, NGC 6712 (Scutum); Cr 399 (asterism), M27, NGC 6802, NGC 6823, NGC 6834, NGC 6940, St 1 (Vulpecula)
Top ten binocular deep-sky objects for August: Cr 399, IC 4756, M8, M11, M17, M22, M24, M25, M27, NGC 6633 (IC 4756 and NGC 6633 are collectively known as the Binocular Double Cluster)
Top ten deep-sky objects for August: M8, M11, M16, M17, M20, M22, M24, M27, M55, M57
Challenge deep-sky object for August: Abell 53 (Aquila)
The objects listed above are located between 18:00 and 20:00 hours of right ascension.