Mercury
Mercury reaches superior conjunction on May 11th and as result for most of May is unsuitably placed for observation. Only at the end of the month does the chance arise to glimpse the elusive planet; but it won't be easy. For example, from latitude 51.5N (London, England) Mercury is a mere 4 degrees above the northwestern horizon, 45 minutes after sunset on May 23th. The situation is marginally better on May 31st, with Mercury now 7 degrees high.
During this time the planets brightness decreases from magnitude -0.9 to -0.3. With lengthening twilight, northern hemisphere based observers may find spotting the planet difficult with the naked eye. Binoculars will assist greatly but of course only scan the sky when you're sure that the Sun has set and therefore out of harms way.
What always helps in a search like this is a nearby brighter marker. And this time we have one! From May 23rd to May 25th, Mercury will pass just over a degree north of the much brighter Venus (mag. -3.9). Also located a few degrees from the pair is Jupiter (mag. -1.9). However despite being more than twice as bright as Mercury, the giant planet is over six times fainter than Venus.
Observers located at southern temperate latitudes also have the chance to spot Mercury at the end of the month, but the planet is even lower above the horizon than for their northern counterparts.
Venus
Having past through superior conjunction at the end of March, Venus is now moving slowly east of the Sun. Now shining at magnitude -3.9, the planet should be visible to those at northern temperate latitudes and in the tropics during the last week of May. It will appear low down towards the northwest after sunset in the twilight sky. On May 4th, Venus moves from Aries into Taurus where it remains for the rest of the month. Its current northern declination makes the planet more difficult to spot for those living in the southern hemisphere.
Venus will pass less than one degree north of Jupiter on May 28th with Mercury passing just over a degree north of Venus between May 23rd and May 25th.
Mars
Mars reached solar conjunction last month and remains too close to the Sun to be safely observed this month.
Jupiter
Jupiter's long evening period of visibility is now almost at an end. The planet reaches solar conjunction on June 19th and by the end of May will be lost to the bright glare of the evening twilight. Now down to magnitude -1.9, Jupiter is visible low down towards the west-northwest from about 45 minutes after sunset for those located in the tropics and at northern temperate latitudes. As a consequence of its northerly declination amongst the stars of Taurus, opportunities to glimpse the planet from southern latitudes are even more fleeting.
As previously stated, by the end of May Jupiter will be effectively unsuitably placed for observation, however a possible final chance to spot the planet occurs on May 28th. This is when six times brighter Venus will pass less than one degree north of Jupiter. The pair should by visible very low above the northwestern horizon as soon as it's dark enough.
Saturn
The famous ringed planet has just passed opposition (April 28th) and remains superbly placed for observation during May. Saturn is visible towards the east-southeast as darkness falls and can be observed practically all night. The planet starts the month in western Libra on a retrograde motion that takes it back into neighbouring Virgo on May 13th.
Now past opposition the apparent brightness and apparent size of Saturn will gradually decrease as the distance between the two planets increases. During May, its magnitude decreases from 0.1 to 0.3 with the apparent diameter shrinking only slightly from 19 to 18.5 arc seconds.
Saturn is positioned 14 degrees to the east of Spica (mag. 1.0), the brightest star in the constellation Virgo. When viewed with the naked eye, Saturn appears cream coloured and about twice as bright as blue-white Spica. Through binoculars the planet appears slightly elongated, hinting at its famous set of rings. Also visible with binoculars when positioned a reasonable angular distance from the planet, is Saturn's brightest moon Titan (mag. 8.4). Much more difficult to detect is fainter Rhea (mag. 9.8), the second largest moon of Saturn.
Saturn in Libra during May 2013 - pdf format
Saturn's wonder of course is its ring system. They are currently tilted at 19 degrees from our perspective and even a small 80mm (3.1-inch) telescope will easily show them. At magnification 100x the rings are nicely visible, tightly circling the central gem of Saturn. Increase the magnification to 200x or greater (seeing permitting) and the ring shadow on the planet, the darker outer A ring, the lighter B ring, subtle shadings and colour changes on Saturn's surface may be detected.
A good quality larger telescope, with its increased light gathering capability and higher magnification capability will of course show greater detail. For example, a 200mm (8-inch) scope can under good seeing be used to up to 400x magnification and will also reveal the 0.7 arc seconds wide Cassini division, the Enke division, the hazy C-ring as well as up to half a dozen of Saturn's satellites.
The almost full Moon passes 4 degrees south of Saturn on May 23rd.
Uranus
Currently located in Pisces, Uranus (mag. 5.9) is not suitable placed for northern hemisphere observers during May, but is visible as an early morning object for those located further south.
On May 7th, the waning crescent Moon passes 4 degrees north of Uranus.
Neptune
Neptune, magnitude 7.9, is located in Aquarius and is visible as a very early morning object from northern latitudes during the latter part of May. It's better placed from the tropics and southern hemisphere where it can be seen in the early morning May sky.
The last quarter Moon passes 6 degrees north of Neptune on May 4th and May 31st.
Solar System Data Table May 2013
| Date | Right Ascension | Declination | Mag. | Size | Illum. (%) | Distance from Earth (AU) | Constellation | |
|---|---|---|---|---|---|---|---|---|
| Sun | 5th May 2013 | 02h 48m 04.6s | 16d 10m 55.9s | -26.7 | 31.7' | 100 | 1.009 | Aries |
| Sun | 15th May 2013 | 03h 27m 06.9s | 18d 48m 27.8s | -26.7 | 31.6' | 100 | 1.011 | Taurus |
| Sun | 25th May 2013 | 04h 07m 04.1s | 20d 54m 14.2s | -26.7 | 31.6' | 100 | 1.013 | Taurus |
| Mercury | 5th May 2013 | 02h 18m 15.7s | 12d 40m 49.5s | -1.4 | 05.1" | 96 | 1.310 | Aries |
| Mercury | 15th May 2013 | 03h 42m 07.6s | 20d 18m 29.5s | -2.0 | 05.1" | 99 | 1.309 | Taurus |
| Mercury | 25th May 2013 | 05h 10m 05.3s | 24d 53m 42.5s | -0.9 | 05.7" | 80 | 1.179 | Taurus |
| Venus | 5th May 2013 | 03h 27m 13.7s | 18d 34m 58.1s | -3.9 | 09.8" | 99 | 1.695 | Taurus |
| Venus | 15th May 2013 | 04h 18m 06.2s | 21d 33m 31.4s | -3.9 | 10.0" | 98 | 1.675 | Taurus |
| Venus | 25th May 2013 | 05h 10m 35.1s | 23d 32m 26.8s | -3.9 | 10.1" | 97 | 1.649 | Taurus |
| Mars | 5th May 2013 | 02h 33m 02.8s | 14d 47m 47.9s | 1.3 | 03.8" | 100 | 2.451 | Aries |
| Mars | 15th May 2013 | 03h 02m 04.1s | 17d 04m 13.8s | 1.3 | 03.8" | 100 | 2.459 | Aries |
| Mars | 25th May 2013 | 03h 31m 23.7s | 19d 03m 28.7s | 1.4 | 03.8" | 100 | 2.464 | Taurus |
| Jupiter | 5th May 2013 | 05h 08m 32.4s | 22d 35m 56.1s | -2.0 | 33.3" | 100 | 5.914 | Taurus |
| Jupiter | 15th May 2013 | 05h 17m 48.7s | 22d 47m 31.9s | -1.9 | 32.9" | 100 | 5.996 | Taurus |
| Jupiter | 25th May 2013 | 05h 27m 23.8s | 22d 57m 14.7s | -1.9 | 32.5" | 100 | 6.061 | Taurus |
| Saturn | 5th May 2013 | 14h 24m 11.9s | -11d 28m 56.6s | 0.1 | 18.8" | 100 | 8.823 | Libra |
| Saturn | 15th May 2013 | 14h 21m 21.4s | -11d 15m 32.3s | 0.2 | 18.8" | 100 | 8.858 | Virgo |
| Saturn | 25th May 2013 | 14h 18m 45.3s | -11d 03m 44.4s | 0.3 | 18.6" | 100 | 8.921 | Virgo |
| Uranus | 5th May 2013 | 00h 38m 59.9s | 03d 28m 00.7s | 5.9 | 03.4" | 100 | 20.877 | Pisces |
| Uranus | 15th May 2013 | 00h 40m 44.7s | 03d 38m 57.8s | 5.9 | 03.4" | 100 | 20.773 | Pisces |
| Uranus | 25th May 2013 | 00h 42m 18.5s | 03d 48m 41.5s | 5.9 | 03.4" | 100 | 20.649 | Pisces |
| Neptune | 5th May 2013 | 22h 27m 52.0s | -10d 18m 39.4s | 7.9 | 02.3" | 100 | 30.323 | Aquarius |
| Neptune | 15th May 2013 | 22h 28m 26.7s | -10d 15m 37.9s | 7.9 | 02.3" | 100 | 30.161 | Aquarius |
| Neptune | 25th May 2013 | 22h 28m 49.4s | -10d 13m 46.3s | 7.9 | 02.3" | 100 | 29.993 | Aquarius |