Night sky in May Highlights

28th/29th May Asteroid Ceres at opposition.

The chart below shows the night sky on the 1st May around 10 pm. The only evening planet is Mars, now low in the western sky after sunset. The bright planets Jupiter and Saturn are on their way but still only observable to the early morning astronomer. The main area of interest to the evening astronomer is Virgo with its many galaxies. We also have a “Blue Moon” this month, more about this than you’ll ever want to know below, and the first asteroid to be discovered “Ceres” is at opposition at the end of May.

For visual observers with a “largish” telescope there is the challenge of trying to see an object over 2 billion light-years away.

Moon Phases

May 5 New Moon

May 12 First quarter

May 18 Full Moon

May 26 Last quarter

The full Moon on 18th is called a “Blue Moon”. Why? Normally there are only 3 full moons in a season, (astronomically defined as the period between a solstice and an equinox) with each full moon having been given a traditional name. Occasionally a season will have 4 full moons. But in order to maintain the religious calendar it was important that the last moon in a season maintained its original name, so it is the 3rd moon that is the additional one and called a “Blue Moon”.

The next Blue Moon will be in August 2021.

Some may have heard the definition of a “Blue Moon” as being the second Full Moon within a calendar month. This is a recent invention thought to have stemmed from a misprint in the American magazine “Sky and Telescope” in March 1946. Unfortunately this was used as source material for a radio broadcast, which started its popularisation.

Why the term “Blue”? No one is really sure, but one suggestion is that it’s from an old English word meaning ‘to betray’, because this 3rd moon was too early in the season and might betray the calculations the clergy used to determine the dates for Lent and Easter in the Christian calendar.

Planets (all times are Local Spanish time)

Mercury:- Mercury passes behind the Sun on the 21st of May, so is always too close to the Sun to be really observable this month.

Venus:- Venus is also an early morning object, but now too close to Sun to be properly observable.

Mars:- Mars appears low in the western sky after sunset but will have set before midnight.

 Jupiter:- Jupiter rises late in the evening, so doesn’t get high enough to be properly observed until after midnight. It is at its highest elevation, about 28º about 5am at the beginning of the May, but getting earlier, so by the end of May it crosses our meridian at 2:45am. Still a bright early morning object for those up before sunrise.

Saturn:- Saturn is following a similar path to Jupiter, but is approximately 2 hours behind Jupiter. So by the end of the month it will be at its highest elevation of 29º above the southern horizon around 5 am..

Uranus:- Uranus passed behind the Sun during April, and is still too close to the Sun to be properly observed this month

Neptune:- Neptune recently passed behind the Sun and is still too close to the Sun to be properly observed at the start of the May. But by the end of the month it is an early morning object rising about 3 am and having an elevation of 23º above the south-eastern horizon as dawn breaks around 5:17.

Meteor Showers

There are 2 meteor showers that peak this month, the Eta Aquarid that peaks on the 8th but the radiant source will be so far south that you would be lucky to see any from here, and the Alpha Scorpiid that peaks on the 13th May. Its radiant source is just above the star Antares and with its low rate and a 1st quarter Moon you will be unlikely to see any until well after midnight.


For those dedicated or desperate to photograph a different comet this month, comet “C/2017 M4 (ATLAS)” reaches its peak magnitude of 12.8 to 13 around the 2nd or 3rd of May. The best time is 3:45 am when it will be due south, 13 to 14 degrees above the horizon.

Ceres the first Asteroid

The biggest asteroid “Ceres” reaches opposition (when it’s at its closest and brightest as viewed from Earth) on May 28th at 23h Universal Time. Although with a magnitude close to 7 it’s still not a naked eye object but should be visible through binoculars. Unfortunately the best time (when it’s due south and at its highest angle of elevation) is around 2am in the morning of the 29th of May (Thank’s to Spain being on Central European Summer Time rather than its more natural GMT).

Ceres, with an average diameter of 976 Km and only about 1/80 the mass of our Moon, is too small to hold on to a permanent atmosphere, but astronomers sometimes detect a thin layer of water vapor around this asteroid, but its presence is very variable.

The Dawn space probe went into orbit around Ceres in March 2015, and is still there after its mission finally ended in October 2017. But data from the probe suggests that this variable atmosphere is the result of random coronal mass ejections from our Sun, with the high energy particles smashing into the asteroid’s surface and freeing water molecules to create a temporary atmosphere.

Really DEEP DSO’s(deep sky objects)

For those up for the challenge of seeing something really far away, if you have a telescope of at least 6” diameter the most distant thing you can see with it using your eye is the Quasar 3C 273, it is in the constellation of Virgo and is due south around 11pm (depending upon date). You will need a detailed finder chart (Google or see link below) to identify it as it will only appear as a dim 13 magnitude star, but it is about 2.5 billion light years away. While an 8” scope is better, it has been seen by people using only a 6” scope.

Some other Deep Sky Objects for evenings in May, include:-

M109 mag 9.8 Galaxy in Ursa Major 8 x 5 arcmin

Caldwell 26 (NGC 4244) mag 10.2 Galaxy in Canes Venatici 16 x 2 arcmin

M106 mag 8.4 Galaxy in Canes Venatici 18 x 8 arcmine

M100 plus neighbour NGC 4312 mag 9.3 & 12 Pair of galaxies in Coma Berenices 7×6 arcmin

M86 + M84 mag 9 – 10 Markarian’s chain, a string of galaxies that form part of the Virgo

Galaxy Cluster, which contains thousands of galaxies over a 10º area of sky.

Caldwell 38 (NGC 4565) mag9.6 Galaxy in Coma Berenices. 16 x 3 arc min

M104 mag 8 The Sombrero galaxy in Virgo 9 x 4 arcmin

Caldwell 32 (NGC’s 4631, 4656, 4627) mag 9.-12 Group of galaxies

NGC 4725 mag 9.2 Ring galaxy in Coma Berenices 11 x 8 arcmin

M94 mag 8.2 Spiral galaxy in Canes Venatici

M63 mag 8.6 Sunflower galaxy in Canes Venatici 12 x 8 arcmin

M51 mag 8.4 Whirlpool galaxy in Canes Venatici 11 x 8 arcmin