The night sky in May 2017

posted 28 Apr 2017, 16:03 by Pete Collins
by Anne Holt

Sunrise:       1st    05.34         31st     04.47
Sunset:        1st    20.39         31st     21.26 

Astronomical darkness:    1st   23.27  to  02.43        31st   none

Full Moon  10th       New Moon  25th

Highlights

Once again it's a problem finding any - there's more light than high.   On 1st of May we have 3 and a quarter hours of astronomical darkness but this rapidly diminishes and from 14th there is none at all until the end of July.  We have one reasonably good meteor shower (as always, weather permitting) and a trio of comets.  The end of the month sees the start of the season for noctilucent clouds.  These are very fine, wispy blue tinged clouds. so high in the atmosphere that they catch the sunlight before sunrise and after sunset.  They could be seen low in the NW, 90 mins to 2 hrs after sunset, and in the NE before sunrise. The ISS is back in the late evening sky from 23May and into June.

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

Still not a good time for planetary observing with only Jupiter particularly prominent this month.

Mercury:  in Pisces, mag 2.4. A morning object throughout May but difficult to see as it remains very low in the sky.  At the start of the month it rises only 20 minutes before the sun.  It reaches Greatest Western Elongation on 17th but is still too low to be seen in the bright dawn sky.  By month end it rises 40 minutes before sunrise, and will have brightened to mag -0.2 but is still not an easy target.

Venus:  in Pisces, mag -4.5. Another one which is very low in the morning sky, so not easy to spot despite its brightness.  It rises just over an hour before the Sun on 1st May, and about 90  minutes before by the end, when it will have dimmed slightly to -4.3 but should be visible in the brightening dawn sky

Mars:  in Taurus, mag 1.6. Sets around 23.00 throughout May but because of the lengthening days the gap reduces during the month, from two and a half hours to 90 minutes after sunset.   Best seen early in the month when it will be to the north of the V shaped Hyades asterism very low in the west, soon after sunset.

Jupiter:  in Virgo,  mag -2.2. Still the only planet putting on a good show, especially in early May, when it is visible for most of the night, setting about 20 minutes before sunrise.   On 7th the 22% lit moon passes to the north of the planet.  By month end it reaches its highest point in the sky only an hour after sunset and sets around 3am. 

There are several transits of the Galilean moons and their shadows, including two brief shadow transits.  On the morning of 12th the shadows of Europa and Io are both on the face of the planet between 02.58 and 03.04 -  a whole six minutes! On 25th we have the shadows of Ganymede and Io for slightly longer, 23 minutes from 01.16 to 01.39. 

Saturn:  in Sagittarius, mag 0.3. Starts the month to the north of the teapot asterism, rising around half an hour after midnight.  On 14th it is 2.3 degrees from the 91% lit Moon, rising about 20 minutes before midnight.   It is currently moving westwards against the background stars (retrograde) and crosses back into Ophiuchus on 19th.
At the end of May it rises at 22.17 and will have brightened slightly to mag 0.1. It remains very low in the sky - max 15 degrees - throughout May but is still worth viewing through a scope as the angle of the rings makes it a beautiful sight.

Uranus:  in Pisces, mag 5.9. Rises 20 minutes before the Sun at the start of May and only 90 minutes before on 31st,  so not visible in the dawn sky.

Neptune:  in Aquarius,  mag 7.9. Not visible in early May, rising a few minutes after 4am, only 90 minutes after the Sun.  By month end it rises soon after 2am and may be seen through a telescope as a small blue disc in the dawn sky.

Meteor Showers

One fairly major shower this month, the Eta Aquarids, dust particles from Halley's Comet, are active between April 19th and May 28th.  The peak is expected on the night of 5th/6th but enhanced activity is probable for a few days either side of this.  ZHR could be anywhere between 10 and 50, depending on which source of information is believed, but is likely to be closer to the lower figure from our latitudes as the radiant is very low and the shower is best seen from the Southern Hemisphere.
These are fast moving meteors, often leaving persistent trails, and may include some Earthgrazers:  bright, long lasting meteors moving horizontally across the sky just before dawn.  This is the best time to view the shower, especially this year when the 85% lit moon doesn't set until 04.14 on the morning of 6th.

Minor Showers

Eta Lyrids:  active 3rd to 12th, peak 9th/10th  ZHR 7.  These originate from comet C/1983 H1 (IRAS Araki-Alcock) and are best seen between 2am and dawn.

The antihelion source, meteors with a radiant on the ecliptic, directly opposite the position of the sun, are active in early May and again towards the end of the month.  ZHR 3-4.

And, in the latter half of May there are a couple of daytime showers -  which isn't much use unless you happen to have radio or radar detectors.

Comets

C2015/V2 Johnson starts May in Hercules, at mag 7.4, then moves into Bootes on 3rd, spending the rest of the month moving down the eastern edge of the kite asterism.  By month end it should have reached its maximum brightness of mag 6.7.   Best seen in the second half of the month when the Moon is out of the way. 

41P Tuttle-Giacobini-Kresak *** is close to Vega in Lyra at the start of May, then moves southwards down the border of Lyra and Hercules during the month.  Starts May at around mag 9 and fades to 10.9 by the end.

71P Clark  starts May in Ophiuchus before moving into Scorpio, finishing the month 2 degrees east of Antares.  Magnitude around 12, making it a telescopic rather than binocular target.

***  Aplologies, last month I referred to this as Tuttle-Giacobini-Knesal.  Obviously can't read my own writing in my notes.  Did anybody spot this? (the mistake, not the comet)

For more more detailed positions of planets and comets see
http://in-the-sky.org
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