The night sky in May 2018

posted 28 Apr 2018, 04:56 by Pete Collins   [ updated 28 Apr 2018, 05:40 ]
by Anne Holt

Sunrise:      1st    05.34           31st   04.47
Sunset:       1st    20.38           31st   21.26

Astronomical darkness: 1st   23.26  to  02.45           31st     none
On 13th it begins at 00.39 and ends at 01.30 - and that's it until the end of August.  Though in our light polluted sky we're unlikely to notice much difference.

New Moon:  15th at 12.47
Full Moon:    30th at 01.58
This is known as the Flower Moon, for reasons which will be obvious to gardeners and Gilbert and Sullivan fans.

Highlights

Venus and Jupiter are both unmissable at the moment and Mars and Saturn are brightening slightly, though still very low in the sky.  We have one major meteor shower, marred by the presence of the gibbous Moon, and a small amount of astronomical darkness in the first half of the month.  Late May sees the start of the Noctilucent Cloud season. These are fine, wispy, blue tinged clouds so high in the atmosphere that they catch the sunlight before sunrise and after sunset.  They might be seen, low in the NE , 2 hours to 90 minutes before sunrise and in the NW 90 minutes to 2 hours after sunset.  Bright passes of the ISS are well after midnight for most of the month, and then late evening towards the end of the month. And we might see an end to all these April showers.  Fingers crossed that they aren't replaced by May showers!

Constellations

As the sky darkens at the start of the month Lyra and Cygnus are rising in the north east, followed a couple of hours later by Aquila.  In the later part of the night the Summer Triangle formed by Vega, Deneb and Altair, the brightest star in each of these three constellations, should be easily visible. By the end of the month Aquila will be above the horizon by around 11pm. The brightest part of the Milky Way visible to us in the UK runs through the Summer Triangle and down through Scutum and Sagittarius.

The Plough is still very high in the sky for most of the night, standing on its handle, so Cassiopeia, the W shaped 'Lady in the Chair',  on the opposite side of the Pole Star is very low down in the north.

Bootes, the herdsman, is now riding high although only Arcturus, the brightest star in the celestial northern hemisphere, is above magnitude 2, so its kite asterism may not be easily visible in our light polluted skies. Arcturus is easy to find though - just follow the arc of the Plough's handle down to the south until you come to Arcturus.  Carry on the arc a bit further and you come to the star Spica, the brightest star in Virgo.

At this time of year when you look up to the south you are looking out of the plane of our Milky Way galaxy instead of along it like you do in winter and summer, so there aren't many bright stars, open star clusters and nebulae. However, if you've got a telescope this is a good time of year to hunt down globular clusters like M13, the Great Globular Cluster in Hercules, and faint galaxies like the many galaxies lying in the bowl of Virgo and into Coma Berenices.

Planets

Mercury:  moving through Cetus, Pisces, Cetus again, Aries and Taurus,  mag 0.3. A morning object, barely visible in May despite brightening to mag -1.6 by month end, as it rises less than half an hour before the Sun throughout.

Venus:  in Taurus mag -3.9. Unmissable in the western sky after sunset. (weather and tall buildings permitting).  On 1st it sets at 23.14 and is 17 degrees above the horizon as the sky darkens around 21.00.  It gets lower in the sky during the month as the angle of the ecliptic decreases, but its apparent distance from the Sun is still increasing. On 17th the 7% lit Moon passes 5 degrees south of the planet.  It moves into Gemini on 20th, by which time it will have brightened to mag -4.0.  By 31st it sets at 00.15, two and three quarter hours after the Sun.     

Mars:  in Sagittarius,  mag -0.4. Getting brighter during May as it gets closer to us.  On 1st it rises at 02.27 and reaches an altitude of 11 degrees in the south before the sky begins to brighten. On 6th the 68% Moon passes 2.5 degrees to the north west. It moves into Capricorn on 15th and will be at mag -0.7.  On 31st, when it will have reached mag -1.2, it rises at 01.12 and culminates at 05.06, soon after Sunrise.  Its brightness and orange red hue will mean it easily stands out against the fainter stars of Capricorn.

Jupiter:  in Libra,  mag -2.5. Shining brightly for most of the night throughout May.  On 1st it is just above the horizon as the Sun sets and should be easily visible by about 22.00.  It culminates at 01.41, when it will be 20 degrees above the southern horizon.  Reaches opposition on 9th, when it is at an altitude of 21 degrees at around 1am (midnight in real time).  On 27th it is 3.5 degrees from the almost full Moon.  On 31st it culminates at 23.25.   This month is a good time to look at Jupiter through a scope, even a fairly small one should show the 2 main belts and the 4 Galilean moons. A slightly larger instrument should show more detail, including the great red spot. There are several moon and shadow transits this month.  Details can be found in any astro mag.

Saturn:  in Sagittarius, mag 0.4. On 1st it rises at 01.20 and culminates just before Sunrise, 13 degrees above the southern horizon at dawn.  On 15th, the three quarter Moon passes the planet 3.5 degrees to the east.   Saturn also brightens during the month, reaching mag -0.2 by 31st, when it culminates at 03.07.  It's still very low, 14 degrees above the southern horizon, just above the Teapot asterism.  However, the rings are wide open, so it's worth looking at through a scope if you have a viewing site with a low, clear southern horizon.

Uranus:  not visible

Neptune:  in Aquarius, mag 7.9. Not visible for most of May, rising only 17 minutes before the Sun on 1st.  By 31st it rises at 02.15,  2.5 hours before Sunrise but still doesn't get much above the horizon as the sky brightens. WARNING:  Don't try to observe it through a scope at this time - catching even the first rays of the rising sun would blind the observer.

Dwarf Planets

Ceres: in Cancer, mag 8.4. A possible target for a small scope.  On 1st it sets at 04.53 and at 02.54 on 31st, when it is 21 degrees above the horizon at dusk.

Haumea in Bootes, mag 17.3, and Makemake in Coma Berenices, mag 17.0, are both quite well placed this month but are out of range of amateur scopes,  They could, however, be targets for keen astrophotographers.

For exact positions of all solar system objects at any time see:
Dwarf planets can be found under 'asteroids'

Meteors

One major shower. Eta Aquarids, active April 19th to May 28th,  date of peak varies according to information source but the majority give it as the early hours of 6th or 7th.  ZHR 10 - 30.  They are fast moving (42 mps) meteors, some with trails, originating from debris left by Halley's Comet. The shower is best seen from further south - between the equator and the tropic of Capricorn the ZHR could be as high as 60.  From here the radiant rises just before dawn, unfortunately this year the Moon rises at 01.26 on 6th and 02.28 on 7th, so will seriously interfere.  Rates are said to be quite good for a few days either side of the peak but the Moon will be in the way in the early hours throughout this period.

Eta Lyrids,  active 3rd to 12th, peak 9/10th. ZHR 3, although as usual some sources disagree and give a figure as high as 7.   Parent comet is C/1983/H1 (IRAS Araki - Alcock) and the shower is best seen just between 2am and dawn.  The Moon rises at 03.48 on 10th, giving just under 2 hours of optimum viewing conditions - as always, weather permitting. 

The Antihelion Source (meteors, having a radiant on the ecliptic opposite the position of the Sun, which can't be attributed to a particular shower) is active in the latter part of May:  ZHR 1-3.

There are also several daytime showers in late May but they can only be detected using radar or radio equipment.

Comets

Still nothing brighter than mag 10.5.  The next possible naked eye comet is 21P  Giacobini-Zinner, currently magnitude 15.7, which is predicted to reach naked eye brightness in late August and September.

For positions of comets which are currently visible see;
www.cometwatch.co.uk/current-observable-comets/
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