Mercury reached greatest eastern elongation last month and was visible as an early evening object during the first three weeks of June. For this month the role will be reversed; the fast moving planet first passes through inferior conjunction on July 9th, before swapping to the morning sky soon after.
Although visible during the latter part of July, for most of the month Mercury is unsuitably placed for observation. The chance to glimpse this small world starts from about July 25th, but it's very low down. On this date, Mercury appears only 4 degrees above the east-northeast horizon, 45 minutes before sunrise (from northern temperate latitudes). At magnitude +1.2 and set against the bright morning twilight, spotting Mercury requires a clear unobstructed view of the horizon and probably at least a pair of binoculars to be seen. However, the situation does slightly improve as the month progresses. On July 30th, the date of greatest western elongation (20 degrees), the planet hovers 7 degrees above the horizon, with an increased magnitude of +0.1. The illuminated phase of Mercury during this time frame increases from 23% to 37%. Also note, positioned just a few degrees north of Mercury are planets Jupiter and Mars.
From southern temperate latitudes Mercury also appears low down, only 6 degrees above the horizon, 45 minutes before sunrise. But astronomers living in this part of the World have it marginally easier than their northern counterparts; they don't have to battle against the long summer morning twilight.
Venus remains visible as an early evening object towards the west-northwest horizon during July. Despite the planet continuing to distance itself from the Sun it's still rather low down for observers living at northern temperate latitudes. The visibility and altitude of Venus is slightly better during the early part of the month, although at magnitude –3.9, observers won't have problems spotting the planet against the bright evening twilight. For example on July 10th, from London, England (51.5N) Venus is 5 degrees above the horizon, 45 minutes after sunset. However, the planet sets less than 80 minutes after the Sun. By the end of the month, this has decreased to 4 degrees altitude and 75 minutes.
From equatorial and southern temperate latitudes, Venus is much better placed for observation. For example, on July 10th from latitudes of 35S (approx. equal to Sydney, Cape Town and Santiago) Venus is 14 degrees high, 45 minutes after sunset and sets 2 hours after the Sun. This improves to 20 degrees and 2.5 hours respectively at the end of the month.
During July, the apparent diameter of Venus increases slightly from 11 to 12 arc seconds with its phase decreasing from 90% to 83%. On July 10th, the 7% illuminated waxing crescent Moon passes 7 degrees south of Venus. Later on July 22nd, the planet passes 1.2 degrees north of Regulus (α Leo – mag. +1.4) the brightest star in Leo "The Lion".
Mars is slowly becoming easier to see against the early morning twilight as the Sun continues to distance itself from the planet in the sky. At magnitude +1.6, the famous "Red planet" hovers low above the east-northeast horizon about one hour or so before sunrise. Keen eyed observers can spot the planet with the naked eye although it won't be easy, especially during the early part of the month. Binoculars are probably a good option for most. The apparent size of Mars hasn't changed much recently; it's still small at just 3.8 arc seconds and therefore surface details are unlikely to be visible through a telescope.
Mars is currently moving direct and starts the month in Taurus before crossing the constellation boundary into Gemini on July 14th, where it remains for the rest of the month. On July 6th, the thin 3% illuminated waning crescent Moon passes 4 degrees south of Mars with Mars passing only 0.8 degrees north of the much more brilliant Jupiter (mag –1.9) on July 22nd.
Jupiter, magnitude –1.9, passed solar conjunction last month and is now rising slightly earlier each day. It's visible as a conspicuous object amongst the stars of Gemini in the early morning July sky. Although, the largest planet of our solar system is currently positioned too low above the east-northeast horizon for serious telescopic observation it's still an impressive naked eye sight.
A nice planetary conjunction occurs on July 22nd, when the much fainter Mars (mag. +1.6) passes less than a degree north of Jupiter. Since Mars is about 25x the fainter of the two, Jupiter acts as a bright finder aid when searching for the "Red planet". Both objects should fit nicely in the same low magnification telescope field of view.
At months end, Jupiter's apparent size stands at about 33 arc seconds and the planet rises approximately 2 hours before the Sun.
Saturn starts July moving retrograde in eastern Virgo until it reaches its second stationary point on the 11th. The planet then reverses back to direct motion as this year's opposition period comes to an end. From mid northern hemisphere latitudes the planet is visible as soon as it gets dark towards the southwest before setting around or just after midnight. Due to Saturn's current southerly declination it won't appear very high above the horizon for those observers but from southern and tropical latitudes the planet is much higher in the sky and the period of visibility is considerably better.
The solar systems second largest planet shines at magnitude +0.6 and has an apparent size of 17 arc seconds. It's located less than one degree south of magnitude +4.2 star kappa (κ) Virginis.
On July 17th, the first quarter Moon passes 3 degrees south of Saturn.
Uranus, magnitude +5.8, is now well positioned for observation amongst the stars of Pisces in the early morning sky. The far away planet rises in the east during the early hours of the morning at the start of the month, improving to before midnight by months end. It then remains visible for the remainder of the night.
On July 18th, Uranus reaches its first stationary point, after which it begins retrograde motion. The planet is visible to the naked eye from a dark site and is an easy binocular target. Although Uranus exhibits only a small 3.6 arc seconds apparent diameter, telescopically it has a definite green hue and at magnifications of 100-150x the planet disk is easily apparent, although distinguishing any surface details is difficult.
On July 27th, the 68% illuminated waning gibbous Moon passes 3 degrees north of Uranus.
Neptune (mag. +7.8), the most distant planet in the solar system is now fast closing in on August’s opposition and hence its visibility continues to improve as July progresses. Since the planet is located in the southern zodiac constellation of Aquarius with a declination of -10 degrees it's currently better placed for observation for observers located in either the tropics or southern hemisphere.
At the start of July, Neptune fights against the early dawn twilight for those located at temperate northern latitudes but as the month progresses and the nights become gradually longer, it becomes easier to see. It's a much easier target from the tropics and southern hemisphere where the planet rises in late evening at the beginning of July and a couple of hours earlier by month's end.
Neptune is positioned about 1 degree to the west of Sigma (σ) Aquarii mag. +4.8. The planet is too faint to be seen with the naked eye but is visible with binoculars.
On July 25th, the 91% illuminated waning gibbous Moon passes 6 degrees north of Neptune.
Solar System Data Table July 2013
|Date||Right Ascension||Declination||Apparent Magnitude||Apparent Size||Illum. (%)||Distance from Earth (AU)||Constellation|
|Sun||5th July 2013||06h 56m 20.0s||22d 48m 21.7s||-26.7||31.5'||100||1.017||Gemini|
|Sun||15th July 2013||07h 37m 11.6s||21d 33m 34.6s||-26.7||31.5'||100||1.016||Gemini|
|Sun||25th July 2013||08h 17m 12.3s||19d 42m 13.3s||-26.7||31.5'||100||1.016||Cancer|
|Mercury||5th July 2013||07h 25m 47.7s||17d 52m 09.3s||4.5||11.8"||03||0.569||Gemini|
|Mercury||15th July 2013||07h 01m 03.6s||17d 49m 04.9s||4.0||11.2"||04||0.603||Gemini|
|Mercury||25th July 2013||06h 59m 29.1s||19d 26m 29.4s||1.1||08.9"||23||0.756||Gemini|
|Venus||5th July 2013||08h 46m 08.6s||19d 41m 02.8s||-3.9||11.2"||89||1.484||Cancer|
|Venus||15th July 2013||09h 34m 43.6s||16d 07m 59.5s||-3.9||11.7"||87||1.431||Leo|
|Venus||25th July 2013||10h 21m 10.0s||11d 53m 20.1s||-3.9||12.2"||85||1.373||Leo|
|Mars||5th July 2013||05h 33m 42.5s||23d 43m 51.9s||1.5||03.8"||99||2.449||Taurus|
|Mars||15th July 2013||06h 03m 27.3s||23d 58m 04.6s||1.6||03.8"||98||2.434||Gemini|
|Mars||25th July 2013||06h 32m 51.3s||23d 51m 24.6s||1.6||03.9"||98||2.415||Gemini|
|Jupiter||5th July 2013||06h 08m 03.1s||23d 13m 13.3s||-1.9||32.2"||100||6.120||Gemini|
|Jupiter||15th July 2013||06h 17m 50.4s||23d 11m 04.7s||-1.9||32.4"||100||6.084||Gemini|
|Jupiter||25th July 2013||06h 27m 23.6s||23d 06m 46.7s||-1.9||32.7"||100||6.029||Gemini|
|Saturn||5th July 2013||14h 12m 51.3s||-10d 43m 04.0s||0.5||17.6"||100||9.418||Virgo|
|Saturn||15th July 2013||14h 12m 54.5s||-10d 46m 11.5s||0.6||17.4"||100||9.577||Virgo|
|Saturn||25th July 2013||14h 13m 35.4s||-10d 52m 34.6s||0.6||17.1"||100||9.741||Virgo|
|Uranus||5th July 2013||00h 46m 12.6s||04d 12m 11.8s||5.8||03.5"||100||20.008||Pisces|
|Uranus||15th July 2013||00h 46m 26.7s||04d 13m 20.3s||5.8||03.6"||100||19.841||Pisces|
|Uranus||25th July 2013||00h 46m 22.8s||04d 12m 35.8s||5.8||03.6"||100||19.679||Pisces|
|Neptune||5th July 2013||22h 28m 15.6s||-10d 18m 25.6s||7.9||02.3"||100||29.348||Aquarius|
|Neptune||15th July 2013||22h 27m 38.8s||-10d 22m 16.7s||7.8||02.3"||100||29.225||Aquarius|
|Neptune||25th July 2013||22h 26m 53.2s||-10d 26m 57.4s||7.8||02.3"||100||29.123||Aquarius|