The Planets this Month - August 2016

Mercury

Mercury reaches greatest eastern elongation on August 16th when it moves out to 27.4 degrees from the Sun. From southern and tropical latitudes the planet is visible in the early evening sky throughout the month. This also happens to be the most favourable evening apparition of the year from such locations. In addition, there is the added bonus that during this time Venus and Jupiter are in the same region of sky.

The diagram below shows the view looking west 45 minutes after sunset between July 22nd and September 10th from latitude 35S, approx. equal to Sydney, Cape Town and Santiago. The view will be slightly different from other southerly latitudes.

During the main visibility period from July 22nd to August 31st, Mercury fades from mag. -0.6 to +1.0. From about mid-August, Jupiter (mag. -1.7) can be used as a useful guide to locating fainter Mercury. During the last few days of August and into September brilliant Venus (mag. -3.8) also acts as a helpful locater. On August 4th and 5th, the thin waxing crescent Moon enters the frame, enhancing the splendid evening viewing.

Although Mercury reaches greatest elongation east this month due to the angle of the ecliptic and bright evening twilight, observers at northern temperate locations will find it challenging to glimpse the elusive world. The planet at best appears low down close to the western horizon and from many locations won't be visible at all.

Venus

Venus, mag. -3.8, continues to move out from the Sun in the evening sky this month. The planet became visible last month low down above the west-northwestern horizon just after sunset for observers at tropical and southern latitudes, improving slightly in altitude each subsequent evening. At the beginning of August it can also be seen very low down above the western horizon from regions such as southern Florida and the Mediterranean but will take up to a couple of weeks more to be easily visible for those living further north.

As previously mentioned superb views occur on the evenings of August 4th and 5th when Venus, Jupiter, Mercury and the Moon are strung out in a line above the western horizon during twilight. The spectacle will be readily visible to all those at tropical and southern latitudes. Also on August 5th, Venus passes one degree north of first magnitude star Regulus (α Leo - mag. +1.4).

The closest planetary conjunction of 2016 occurs on August 27th when Venus passes a mere 4 arc minutes north of Jupiter, a separation equivalent to only 1/8 the diameter of the full Moon. Venus appears in the sky seven times brighter than Jupiter and although they seem incredibly close together, in reality Venus is more than 4 times nearer to Earth.

Mars

Mars remains an evening object throughout August although its visibility period is now reducing. At the beginning of the month the "Red planet" can be seen after sunset towards the southwest, remaining visible until around midnight from mid-northern temperate latitudes. By months end it sets about an hour earlier. However, those living at more southerly locations have it rather better. For example, from Sydney, Mars appears high in the northeastern sky at sunset remaining visible throughout the month until the early hours of the morning.

Mars starts the month moving direct (eastwards) in Libra. On August 2nd, it crosses into Scorpius where it remains until August 21st. The planet then cuts through a corner of Ophiuchus for 6 days before returning to Scorpius on August 27th. It stays here until September 2nd when it moves back into Ophiuchus.

This month, the distance between Earth and Mars increases from 108 to 133 million kilometres (67 to 83 million miles). Consequently, the planets magnitude decreases from -0.8 to -0.3 with its apparent size shrinking from 13.0 to 10.5 arc seconds.

On August 11th, the waxing gibbous Moon passes 8 degrees north of Mars. The planet will pass 2 degrees north of Antares (α Sco - mag. +1.0) on August 24th and the following day 4 degrees south of Saturn (mag. +0.5). Mars appears similar in colour to Antares although at mag. -0.5, it's much brighter than the star. Indeed, Antares is often referred to as the "Rival of Mars". Saturn is off-white in colour and can't be mistaken for Mars or Antares.

Mars and Saturn during August 2016 - pdf format (credit:- freestarcharts)

Jupiter

Jupiter, mag. -1.7, continues to be visible as an early evening object towards the west during August although observers at mid-latitude northern temperate regions are likely to lose the planet mid-month. However, it can be seen throughout August from tropical and southern locations. The thin crescent Moon appears close to Jupiter during the evenings of August 5th and 6th. As previously mentioned, Mercury and Venus are also located in the same part of sky and Jupiter will be incredibly close to brilliant Venus on August 27th.

Saturn

Saturn remains a well-placed evening object in Ophiuchus. The planet begins the month moving retrograde before reaching its secondary stationary point on August 13th, after which direct motion is once again resumed. This is often regarded as signalling the end of the year's opposition period. To the naked eye Saturn hardly moves during the month, appearing almost fixed in the sky.

As mentioned above, Mars and bright red supergiant star Antares are also nearby. With Saturn almost stationary what's noticeable this month is the rapid eastward motion of Mars. The "Red planet" starts the month considerably west of Saturn and Antares but by months end has moved east of them both.

From northern locations, Saturn sets well before midnight by months end but some three hours later from those located further south. During August, its brightness decreases slightly from mag. +0.4 to +0.5 with its apparent size marginally decreasing from 17.5 to 16.7 arc seconds.

The waxing gibbous Moon passes 4 degrees south of Saturn on August 12th. Mars passes 4 degrees south of Saturn on August 25th.

Uranus

Uranus, mag. +5.8, is an evening object moving slowly retrograde in Pisces. The distant planet now rises before midnight from northern temperate locations and even earlier for those living further south. To locate Uranus, imagine a line connecting omicron Psc (ο Psc - mag. +4.3) and epsilon Psc (ε PSc - mag. +4.3). The planet is positioned close to the mid-point of this line.

Although faintly visible to the naked eye, Uranus is much simpler to spot with optical aid. Popular 7x50 or 10x50 binoculars easily reveal a "star" like point of light. By observing the planet over a period of time its motion against the "fixed" background stars reveal its true nature.

A small telescope at high magnification will show the planets small green disk (apparent diameter 3.6 arc seconds). However, even when viewed through the largest of amateur scopes it's difficult to make out surface details.

On August 22nd, the waning gibbous Moon passes 3 degrees south of Uranus.

Uranus during August 2016 - pdf format (credit:- freestarcharts)

Neptune

Neptune, mag. +7.8, continues to move retrograde among the stars of Aquarius. With not long to go now before opposition (Sep. 2nd) the most distant planet in the Solar System is superbly placed for observation, rising above the eastern horizon just after sunset, remaining visible for the rest of the evening. With a current declination of 8 degrees south, Neptune is better seen from tropical and southern temperate latitudes where it appears higher in the sky than from further north.

Neptune is the only planet that can't be seen with the naked eye. However, provided you know exactly where to look it's a relatively easy binocular and small telescope target. The planet is currently located about 30 degrees south of the centre of the Great Square of Pegasus and half a degree southwest of lambda Aqr (λ Aqr - mag. +3.7). First magnitude star Fomalhaut (α Psc - mag. +1.2) is another 20 degrees to the south.

Even though the planet's apparent diameter is only 2.4 arc seconds a small scope at high magnification will reveal a small featureless blue disk. Sadly the view is not particularly improved even with larger amateur telescopes. However, it's possible to spot Neptune's largest moon Triton (mag. +14.0) although a scope of at least 300mm (12 inches) aperture is recommended.

On August 19th, the waxing gibbous almost full Moon passes 1.1 degrees north of Neptune with an occultation visible from East Asia and Northwest Canada at 12:03 UT.

Neptune during August 2016 - pdf format (credit:- freestarcharts)

Solar System Data Table August 2016