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Mercury

Mercury passes through inferior conjunction on August 8th. The fast moving planet then moves into the morning sky, reaching greatest elongation west on August 26th. On this day, it will shine at magnitude -0.1 and be positioned 18 degrees from the Sun. From northern temperate latitudes, Mercury will rise 90 minutes before sunrise and be visible very low down above the eastern horizon.

From southern locations, Mercury is not suitably placed for observation this month.

Venus

Venus remains a brilliant early evening object, visible above the western horizon as soon as it's dark enough. On the first day of August, the planet moves from Leo into Virgo where it remains for the rest of the month.

Venus increases in magnitude -4.3 to -4.6, with its illuminated phase decreasing from 57% to 41%. During this time, the planet's apparent diameter increases from 20 to 29 arc seconds. On August 14th, the waxing crescent Moon passes 6 degrees north of Venus offering pleasant early evening viewing. On the last day of the month, Venus passes within 2 degrees of first magnitude Spica (α Vir - mag. 1.0), the brightest star in Virgo.

Moon, Venus and Jupiter in the evening sky from northern temperate locations just after sunset on August 14, 2018 (credit:- freestarcharts)

Mars

Mars remains superbly placed for observation during August. The red planet passed its nearest opposition for 15 years last month, and this month is visible just after sunset and for most of the remainder of the night.

Mars begins August at magnitude -2.8, with an apparent diameter exceeding 24 arc seconds. It's moving retrograde in Capricornus. However, since its distance from the Earth is now increasing, it will fade to magnitude -2.2 with its apparent diameter shrinking to 21 arc seconds by month's end. During the 3rd week of August, the planet moves close to the Sagittarius-Capricornus constellation border. On August 28th, Mars reaches its second stationary point and after that direct motion is resumed. This event is widely regarded as signalling the end of the current opposition period.

With a small telescope, of the order of 80mm (3.1-inch) aperture, and providing recent dust storms have cleared it should be possible to spot details, such as Syrtis Major, on its pink surface.

Mars and Saturn during August 2018 (credit:- freestarcharts)

Mars and Saturn during August 2018 - pdf format (credit:- freestarcharts)

Jupiter

Although fading, Jupiter remains a brilliant evening object moving direct in Libra. It's visible towards the southwest (NH) / north (SH) as soon as it's dark enough. However, by months end it sets well before midnight from northern temperate latitudes, although the visibility is considerably longer for those located further south.

As the month progresses, the giant planet fades from magnitude -2.1 to -1.9 with its apparent size decreasing from 38 to 35 arc seconds. On August 17th, the waxing crescent Moon passes 5 degrees north of Jupiter. On the same day, Jupiter moves to 0.5 degrees of double star, Zubenelgenubi (α Lib - mag 2.7).

Jupiter during August 2018 (credit:- freestarcharts)

Jupiter during August 2018 - pdf format (credit:- freestarcharts)

Saturn

Saturn remains a well-placed evening object moving retrograde in Sagittarius. From mid-latitude northern locations, the ringed planet sets around midnight by months end but over two hours later from those located further south. During August, its brightness decreases slightly from magnitude +0.2 to +0.4 with its apparent size decreasing marginally from 18.0 to 17.3 arc seconds.

The waxing gibbous Moon passes 2 degrees north of Saturn on August 21st.

Uranus

Uranus, mag. +5.8, is a late evening object in Aries. At the beginning of the month, from northern temperate locations, the distant ice giant rises about midnight, improving to a couple of hours before midnight by months end. For those living further south it rises about 30 minutes later than this. On August 7th, the planet reaches its first stationary point, which signals the beginning of this year's opposition period. It then commences retrograde motion.

Although just visible to the naked eye, Uranus is much easier to spot with optical aid. Popular 7x50 or 10x50 binoculars will reveal a "star" like point of light. By observing the planet over a number of nights its slow movement relative to the "fixed" background stars can be noticed.

The waning gibbous Moon passes 5 degrees south of Uranus on August 3rd and 31st.

Uranus during August 2018 (credit:- freestarcharts)

Uranus during August 2018 - pdf format (credit:- freestarcharts)

Neptune

Neptune, mag. +7.8, continues to move retrograde among the stars of Aquarius. The outermost planet reaches opposition on September 7th and is now superbly placed for observation. It rises above the eastern horizon just after sunset, remaining visible for the rest of the evening.

Neptune is always too faint to be spotted with the naked eye. However, it's a relatively easy binocular and small telescope target. The planet can be found about a third of the way along an imaginary line connecting phi Aquarii (φ Aqr - mag. +4.2) with lambda Aquarii (λ Aqr - mag. +3.7). First magnitude star, Fomalhaut (α Psc - mag. +1.2), is about 23 degrees south of Neptune.

Even though its apparent diameter is only 2.4 arc seconds, an 80mm (3.1-inch) refractor at medium to high magnifications will reveal a small featureless blue disk. However, even large amateur reflectors don't significantly improve the view. A scope of at least 300mm (12 inches) aperture is recommended to spot Neptune's largest moon, Triton (mag. +14.0).

On August 27th, the waning gibbous Moon passes three degrees south of the planet.

Neptune during August 2018 (credit:- freestarcharts)

Neptune during August 2018 - pdf format (credit:- freestarcharts)

Solar System Data Table - August 2018

 DateRight AscensionDeclinationMag.App. SizeIllum. (%)Dist. (AU)Constellation
SunAug 0108h 43m 33.6s18d 08m 40.8s-26.731.5'1001.015Cancer
SunAug 1509h 37m 01.3s14d 12m 40.1s-26.731.6'1001.013Leo
SunAug 3110h 36m 01.1s08d 49m 43.3s-26.731.7'1001.010Leo
MercuryAug 0109h 30m 45.9s09d 56m 26.9s2.911.0"80.610Leo
MercuryAug 1508h 54m 36.5s13d 26m 57.6s3.310.2"60.659Cancer
MercuryAug 3109h 29m 51.8s15d 19m 48.0s-0.86.5"611.029Leo
VenusAug 0111h 36m 26.0s02d 36m 40.3s-4.320.4"570.819Leo
VenusAug 1512h 26m 34.0s-04d 14m 22.2s-4.423.6"500.707Virgo
VenusAug 3113h 18m 12.7s-11d 35m 07.6s-4.628.8"410.580Virgo
MarsAug 0120h 26m 03.9s-25d 57m 49.0s-2.824.3"1000.385Capricornus
MarsAug 1520h 12m 12.7s-26d 33m 01.4s-2.523.4"980.400Capricornus
MarsAug 3120h 07m 18.2s-26d 04m 19.9s-2.121.0"940.445Sagittarius
JupiterAug 0114h 46m 25.2s-15d 02m 34.8s-2.137.9"995.201Libra
JupiterAug 1514h 50m 50.4s-15d 25m 51.0s-2.036.4"995.416Libra
JupiterAug 3114h 58m 15.1s-16d 01m 40.2s-1.934.9"995.654Libra
SaturnAug 0118h 14m 18.2s-22d 36m 21.6s0.218.0"1009.218Sagittarius
SaturnAug 1518h 11m 37.4s-22d 39m 06.5s0.317.7"1009.374Sagittarius
SaturnAug 3118h 10m 02.7s-22d 41m 50.1s0.417.3"1009.596Sagittarius
UranusAug 0102h 01m 10.2s11d 45m 16.4s5.83.6"10019.745Aries
UranusAug 1502h 01m 09.3s11d 44m 53.0s5.83.6"10019.515Aries
UranusAug 3102h 00m 24.0s11d 40m 29.9s5.73.7"10019.277Aries
NeptuneAug 0123h 09m 07.9s-06d 31m 19.4s7.82.3"10029.128Aquarius
NeptuneAug 1523h 07m 57.7s-06d 39m 03.9s7.82.4"10029.010Aquarius
NeptuneAug 3123h 06m 24.9s-06d 49m 04.0s7.82.4"10028.940Aquarius