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Mercury

Mercury remains an early evening object for observers located at tropical and Northern Hemisphere latitudes during the first three weeks of May. The planet is located in Taurus and is visible after sunset towards the west-northwest as soon as it's dark enough.

Mercury climbs higher in the sky each evening until it peaks on May 7th, the date of greatest eastern elongation. For example, from 52N (e.g. London, England) the fast moving planet (mag. +0.2) is positioned 11 degrees above the horizon, 45 minutes after sunset. Afterwards its altitude decreases until it's finally lost to the bright twilight sometime during the third week of the month. It should be noted that Mercury is at its brightest before elongation - it fades from magnitude -0.4 to +1.5 during the first half of May. Located a few degrees northeast of Mercury is much more brilliant Venus (mag. -4.3).

The chart below shows positions of Mercury and Venus from latitude 52N (e.g. London, England). The view will be similar from other northern temperate locations.

Mercury evening apparition as seen from latitudes of 52N, 45 minutes after sunset

On May 12th, Mercury (mag. +1.0) passes 8 degrees north of orange giant star Aldebaran (α Tau - mag. +0.9) the brightest star in Taurus. The fast moving planet then reaches a stationary point on May 19th. Retrograde motion follows pulling Mercury back towards the Sun with it arriving at inferior conjunction on May 30th.

From the Southern Hemisphere the planet is not well placed for observation but may be glimpsed extremely low down above the west-northwestern horizon just after sunset at the start of the month.

Venus

Venus continues as a blazing evening object as it heads towards greatest eastern elongation of 45 degrees on June 6th. The planet is so bright that it can't be mistaken and can be spotted even before the Sun dips below the horizon. During May it brightens from magnitude -4.2 to -4.4 with its apparent size increasing from 17 to 22 arc seconds. The phase of the planet decreases from 67 to 54 degrees during the same period.

The period of visibility of Venus varies considerably depending on location. From northern temperate latitudes the planet sets almost 3.5 hours after the Sun at the start of the month, increasing to 4 hours by months end. However, much further south the planet can be seen for as little as 2 hours. On May 21st the waxing crescent Moon passes 8 degrees south of Venus and at the end of the month, Venus passes 4 degrees south of the Gemini twins, Castor (α Gem - mag. +1.6) and Pollux (β Gem - mag. +1.1).

Venus is a brilliant evening star this month (www.freestarcharts.com)

Mars

Mars has now just a few weeks to go before reaching solar conjunction on June 14th. The "Red planet" spends the first few days of May in Aries before moving into Taurus where it remains for the rest of the month. With an apparent magnitude of only +1.5 it's not bright easily lost to the evening twilight and unlikely to be seen this month.

Jupiter

Jupiter is now 3 months past opposition but despite fading in brightness the planet remains a brilliant object in Cancer. The gas giant is moving direct and positioned 7 degrees southeast of beautiful binocular and small telescope open cluster M44 "The Praesepe".

Jupiter is visible as soon as it's dark enough. At the end of the month, it sets just after midnight from northern temperate latitudes but visibility is somewhat shorter for those living in the tropics and further south. The planets magnitude decreases from -2.1 to -1.9 during May with the apparent size diminishing from 38 to 35 arc seconds over the same time period.

On May 24th, the waxing crescent Moon passes 5 degrees south of Jupiter.

Jupiter during May 2015

Jupiter during May 2015 - pdf format

Saturn

Saturn reaches opposition on May 23rd and is therefore visible all night as it continues its slow retrograde motion, starting the month in Scorpius before moving into faint Libra on May 12th. The favourite planet of many astronomers is now at it's stunning best with the rings wide open at a tilt of 24.4 degrees and an apparent diameter of 18.5 arc seconds. Including the rings it spans some 42 arc seconds across. The current southerly declination of Saturn means it's much better placed for Southern Hemisphere or tropical based observers.

Through telescopes, Saturn's rings are a wonderful sight and visible even in the smallest of instruments along with Titan, the largest and brightest moon of Saturn. Larger telescopes reveal subtle planet details and many of the planets other moons.

At opposition, Saturn shines at magnitude +0.1 and is positioned 8.967 AU or approximately 1341 million kilometres (833.5 million miles) from Earth. The full Moon passes 2 degrees north of Saturn on May 5th.

Saturn imaged by the Cassini space probe (NASA)



Saturn during May 2015

Saturn during May 2015 - pdf format

Uranus

Uranus at magnitude +5.9 is currently located in Pisces. For the first half of May from northern temperate latitudes the planet is too down low to be seen against the bright morning twilight. However, the situation quickly improves and by months end Uranus rises over 2 hours before the Sun, therefore visible through binoculars and telescopes against the darker backdrop. Observers located further south have it even better with Uranus well placed in the early morning sky throughout the month. At the start of the May, the planet rises 2 hours before the Sun with the visibility period more than doubling by May 31st.

The waning crescent Moon passes 0.2 degrees north of Uranus on May 15th and an occultation is visible from central South America, west and central Africa (11:55 UT).

Uranus during May 2015

Uranus during May 2015 - pdf format

Neptune

Neptune is a morning object amongst the faint stars of Aquarius, the Water Bearer or Water Carrier. The planet is better placed from tropical and southern latitudes, rising in the east some four hours before the Sun at the beginning of the month. By months end it can be seen around midnight. From Northern temperate latitudes Neptune is better seen towards the end of the month when it rises 3 hours or so before the Sun.

At magnitude +7.9, the Solar System's most distant planet is never bright enough to be visible to the naked eye but can be spotted with binoculars and small telescopes. Telescopes at medium to high magnifications reveal a featureless small blue disk that spans just 2.3 arc seconds across.

The last quarter Moon passes 4 degrees north of Neptune on May 12th.

Neptune during May 2015

Neptune during May 2015 - pdf format

Solar System Data Table May 2015

 DateRight AscensionDeclinationApparent MagnitudeApparent SizeIllum. (%)Distance from Earth (AU)Constellation
Sun5th May 201502h 46m 07.3s16d 02m 09.8s-26.731.7'1001.008Aries
Sun15th May 201503h 25m 05.7s18d 41m 08.2s-26.731.6'1001.011Taurus
Sun25th May 201504h 05m 01.3s20d 48m 40.5s-26.731.6'1001.013Taurus
Mercury5th May 201504h 09m 25.5s23d 39m 06.4s0.007.5"430.894Taurus
Mercury15th May 201504h 42m 01.8s24d 08m 32.2s1.509.7"180.691Taurus
Mercury25th May 201504h 40m 48.3s21d 44m 44.8s4.511.8"030.571Taurus
Venus5th May 201505h 44m 30.6s25d 52m 54.8s-4.217.2"660.969Taurus
Venus15th May 201506h 33m 18.7s25d 56m 03.1s-4.318.7"610.892Gemini
Venus25th May 201507h 20m 01.4s24d 56m 22.3s-4.320.5"570.813Gemini
Mars5th May 201503h 29m 17.6s19d 11m 14.1s1.503.8"1002.479Taurus
Mars15th May 201503h 58m 37.3s20d 51m 38.6s1.503.7"1002.507Taurus
Mars25th May 201504h 28m 12.6s22d 12m 15.6s1.503.7"1002.531Taurus
Jupiter5th May 201509h 04m 40.3s17d 40m 09.1s-2.137.4"995.272Cancer
Jupiter15th May 201509h 08m 17.7s17d 23m 38.1s-2.036.3"995.431Cancer
Jupiter25th May 201509h 12m 52.2s17d 02m 41.0s-2.035.3"995.586Cancer
Saturn5th May 201516h 04m 28.3s-18d 33m 22.0s0.218.4"1009.016Scorpius
Saturn15th May 201516h 01m 31.8s-18d 25m 00.5s0.118.5"1008.977Libra
Saturn25th May 201515h 58m 27.4s-18d 16m 30.9s0.118.5"1008.967Libra
Uranus5th May 201501h 06m 42.6s06d 25m 08.6s5.903.4"10020.896Pisces
Uranus15th May 201501h 08m 36.4s06d 36m 39.4s5.903.4"10020.812Pisces
Uranus25th May 201501h 10m 21.0s06d 47m 09.5s5.903.4"10020.705Pisces
Neptune5th May 201522h 44m 19.7s-08d 49m 04.9s7.902.2"10030.381Aquarius
Neptune15th May 201522h 44m 59.9s-08d 45m 24.9s7.902.3"10030.224Aquarius
Neptune25th May 201522h 45m 28.5s-08d 42m 55.0s7.902.3"10030.058Aquarius