August Celestial Calendar by Dave Mitsky All times, unless otherwise noted, are UT (subtract four hours and, when appropriate, one calendar day for EDT) 8/01 The Moon is 1.7 degrees south-southeast of Uranus at 3:00; a double Galilean shadow transit begins at 10:08; Mercury is in superior conjunction with the Sun (1.342 astronomical units from the Earth, latitude 6.9 degrees) at 14:00; the Curtiss Cross, an X-shaped clair-obscur illumination effect located between the craters Parry and Gambart, is predicted to be visible at 22:20 8/02 Saturn (magnitude +0. 2, apparent size 18.6") is at opposition at 6:00; the Moon is at apogee, subtending 29' 33" at a distance of 404,409 kilometers (251,289 miles) at 7:35; the Moon is 4.8 degrees southeast of the bright open cluster M45 (the Pleiades or Subaru) in Taurus at 11:00 8/03 The Moon is at the ascending node (longitude 68.9 degrees) at 3:00; the Moon is 5.6 degrees north of the first-magnitude star Aldebaran (Alpha Tauri) at 5:00; Mercury is at its northernmost latitude from the ecliptic plane (7.0 degrees) at 6:00 8/05 The Moon is 1.1 degrees north of the bright open cluster M35 in Gemini at 2:00; asteroid 4 Juno (magnitude +10.8) is stationary in Ophiuchus at 4:00 8/06 The Moon is 6.7 degrees south of the first-magnitude star Castor (Alpha Geminorum) at 15:00; the Moon is 3.1 degrees south of the first-magnitude star Pollux (Beta Geminorum) at 20:00 8/07 The astronomical cross-quarter day known as Lammas or Lughnasadh, the midpoint between the summer solstice and the autumnal equinox, occurs today; the Moon is 3.0 degrees north-northeast of the bright open cluster M44 (the Beehive Cluster or Praesepe) in Cancer at 22:00 8/08 A double Galilean shadow transit begins at 12:42; New Moon (lunation 1220) occurs at 13:50 8/09 The Moon is 3.2 degrees north-northeast of Mercury at 6:00; the Moon is 4.5 degrees north- northeast of the first-magnitude star Regulus (Alpha Leonis) at 16:00 8/10 The Moon is 4.0 degrees north-northeast of Mars at 4:00; the Sun enters the constellation of Leo, at longitude 138.2 degrees on the ecliptic, at 15:00 8/11 The Moon is 3.9 degrees north-northeast of Venus at 11:00 8/12 Mercury is 1.1 degrees north-northeast of Regulus at 1:00; the peak of the Perseid meteor shower (a zenithal hourly rate of 100 or more per hour) is predicted to occur at 19:00; asteroid 349 Demboska (magnitude +9.8) is at opposition in Piscis Austrinus at 21:34 8/13 The Moon is 5.5 degrees north-northeast of the first-magnitude star Spica (Alpha Virginis) at 15:00 8/15 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 be visible at 10:28; a double Galilean shadow transit begins at 14:41; a double Galilean shadow transit begins at 15:17; First Quarter Moon occurs at 15:20; a triple Galilean satellite transit occurs at 15:31 8/16 Mars and Neptune are at heliocentric opposition (longitudes 171.6 degrees and 351.6 degrees) at 13:00; the Moon is at the descending node (longitude 247.6 degrees) at 16:00; the Moon is 4.4 degrees north-northeast of the first-magnitude star Antares (Alpha Scorpii) at 22:00 8/17 The Moon is at perigee, subtending 32' 22'' from a distance of 369,125 kilometers (229,363 miles), at 9:16 8/19 Mercury is 0.1 degrees south of Mars at 4:00; asteroid 43 Ariadne is at opposition (magnitude +9.6) in Aquarius at 19:10 8/20 Uranus is stationary, with retrograde motion to begin, at 0:00; Jupiter is at opposition (magnitude -2.9, apparent size 49.1") at 0:00 8/21 The Moon is 3.6 degrees south of Saturn at 0:00 8/22 The Moon is 3.7 degrees southeast of Jupiter at 8:00; Full Moon (known as the Fruit, Grain, Green Corn, or Sturgeon Moon) occurs at 12:02; a double Galilean shadow transit begins at 18:42; the Sun's longitude is 150 degrees at 22:00 8/24 The Moon is 3.7 degrees southeast of Neptune at 6:00; asteroid 89 Julia (magnitude +9.0) is at opposition in Aquarius at 14:22 8/25 The Martian northern hemisphere summer solstice occurs at 0:00 8/26 Mercury is at the descending node through the ecliptic plane at 15:00 8/28 The Moon is 1.4 degrees southeast of Uranus at 11:00 8/29 Venus is at the descending node through the ecliptic plane at 5:00; the Moon is 4.6 degrees southeast of M44 at 19:00; a double Galilean shadow transit begins at 22:43 8/30 The Moon is at apogee, subtending 29' 34" at a distance of 404,098 kilometers (251,096 miles) at 2:22; the Moon is at the ascending node (longitude 66.2 degrees) at 5:00; Last Quarter Moon occurs at 7:13; the Moon is 5.8 degrees north-northwest of Aldebaran at 13:00 8/31 The Curtiss Cross is predicted to be visible at 9:42 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 Jovian satellite 2002 Laomedeia was discovered by Matthew Holman on August 13th, 2002. The peak of the Perseid meteor shower takes place on the night of August 11th/August 12th and is not compromised by moonlight. The periodic comet 109P/Swift-Tuttle is the source of Perseid meteors. The shower’s radiant lies just to the southeast of the Double Cluster (NGC 869 and NGC 884). For more on this year’s Perseids, see page 52 to page 55 of the August 2021 issue of Astronomy and page 48 of the August 2021 issue of Sky & Telescope or click on https://earthsky.org/astronomy-essentials/everything- you-need-to-know-perseid-meteor-shower and https://www.imo.net/viewing-the-perseid-meteor-shower- in-2021/ Information on passes of the ISS, the USAF’s X-37B, the HST, Starlink, and other satellites can be found at http://www.heavens-above.com/ The Moon is 21.8 days old, is illuminated 47.4%, subtends 29.5 arc minutes, and is located in Aries on August 1st at 00:00 UT. The Moon is at its greatest northern declination on August 6th (+25.6 degrees) and its greatest southern declination on August 19th (-25.8 degrees). Longitudinal libration is at a maximum of +5.4 degrees on August 24th and a minimum of -4.9 degrees on August 9th. Latitudinal libration is at a maximum of +6.6 degrees on August 23rd and a minimum of -6.6 degrees on August 10th. Favorable librations for the following lunar features occur on the indicated dates: Crater Piazzi on August 4th, Crater Hayn on August 19th, Crater Compton on August 21st, and Crater Boss F on August 22th. The Moon is at apogee (at a distance 63.41 Earth-radii) on August 2nd and again (at a distance 63.26 Earth-radii) on August 30th and at perigee (at a distance of 57.87 Earth-radii) on August 17th. New Moon (i.e., the dark of the Moon) occurs on August 8th. Full Moon, a Blue Moon by the classic definition of the third Full Moon in a summer that has four, occurs on August 22nd. Browse http://www.lunar- occultations.com/iota/iotandx.htm for information on lunar occultation events. Visit https:/ /saberdoesthestars.wordpress.com/2011/07/05/saber-does-the-stars/ for tips on spotting extreme crescent Moons and https://curtrenz.com/moon.html for Full Moon and other lunar data. Browse https:/ /skyandtelescope.org/wp-content/uploads/MoonMap.pdf and https://nightsky.jpl.nasa.gov/docs/ ObserveMoon.pdf for simple lunar maps. Click on http://astrostrona.pl/moon-map for an excellent online lunar map. Visit http://www.ap-i.net/avl/en/start to download the free Virtual Moon Atlas. Consult http:/ /time.unitarium.com/moon/where.html for current information on the Moon and https:/ /www.fourmilab.ch/earthview/lunarform/lunarform.html for information on various lunar features. See https://svs.gsfc.nasa.gov/4874 for a lunar phase and libration calculator and https://quickmap.lroc.asu.edu/ ?extent=-90,-25.2362636,90,25.2362636&proj=10&layers=NrBsFYBoAZIRnpEoAsjYIHYFcA2vIBvA XwF1SizSg for the Lunar Reconnaissance Orbiter Camera (LROC) Quickmap.