The Night Sky This Month: May 2019

Night Sky 5
Image Credit: Felix Mittermeier

Northern circumpolar constellations, such as Auriga, Cassiopeia, Perseus, Ursa Major, and Ursa Minor, can be seen in the night sky throughout the year. Meanwhile, other constellations are seasonal, and visible only at certain times of year.

Such constellations conspicuous in the south at this time of year include Libra, Scorpius, Serpens Caput (the Serpent’s Head), and Corona Borealis. While all of these constellations contain a great variety of deep sky objects, three star clusters, one in Libra and two in Scorpius, are particularly well placed for observation with modest amateur telescopes.

Read on to discover more about these deep-sky objects, as well as what other star gazing delights to expect for the month ahead.

The Moon in May 2019

Seeing that this month does not offer much in the way of planetary viewing, it may be worth observing the Moon instead. Especially given the fact that Earthshine will be conspicuous on the nights of the 5th and 10th of the month. In the image above, the brightly illuminated part of the Moon surface is lit by sunlight, while the darker parts of the Moon’s disc is illuminated by sunlight reflected off the Earth, hence the term, “Earthshine”.

The Moon Phases in May 2019

New Moon First Quarter Full Moon Last Quarter
May 4th May 12th May 18th May 26th

Note that the Full Moon occurring on the 18th of May will also be Blue Moon, being the third of four full moons to occur during this season. Since full moons occur once every 29.53 days, it can happen that four full moons can occur in one season, and on average, this happens once in every 2.7 years.

Planets in May Night Sky

The month of May is not a good time to observe the planets, since most will be either very low on the horizon, or very close to the Sun. Nonetheless, here is what to expect in terms of planetary viewing during the coming month:

– Mercury will be visible in the early morning sky until about mid-month, which is when it will become lost in the glare of the Sun. By month’s end however, the little planet will become visible in the early evening for about 1.5 hours or so after sunset. Note though that the planet will not rise more than about 5 degrees above the north-western horizon.

– Venus starts the month rising at about 04:00 (GMT), as it moves from the constellation Pisces into the constellation Aries. However, since Venus’ northern declination is now increasing, it will rise progressively earlier until the end of the month, when it will rise at about 03:00 over the east-north-eastern horizon.

– Mars is now approaching the Sun, and although it is still shining at magnitude +1.64 as the month begins, its angular diameter is now scarcely 4 seconds of arc, making it impossible to spot any surface detail with modest amateur equipment. Note though that the planet will remain visible in the north-west until about 23:00 (GMT) throughout May.

– Jupiter will rise at about 23:00 (GMT) in the south in the constellation Ophiuchus. Note, however, that although it will shine at magnitude -2.4, it will not rise above 14 degrees over the southern horizon when it crosses the meridian. While it may not be possible to obtain clear views of the planet without the aid of an atmospheric dispersion corrector, firmly held and well-focused binoculars might reveal the four Galilean Moons as they change their positions around the planet from one night to the next.

– Saturn, will like Jupiter, remain low on the southern horizon when it crosses the meridian. Shining at magnitude +0.9 at the start of the month when it will be about 30 degrees almost due east of Jupiter, it will be a rather conspicuous object when it rises at about 01:00 (GMT). Look for Saturn on the night of the 22nd when it appears as one apex of a triangle made up of Saturn, Jupiter, and a waning gibbous Moon.

Meteor Showers in May 2019

The Eta Aquarids meteor shower is expected to peak on the night of the 6th / 7th, and although the best views of this major meteor shower are had from the southern hemisphere, northern observers can still expect to see a maximum hourly rate of about 30 or so meteors. Note that New Moon occurs on the 4th, which means that the sky will be relatively dark when the peak occurs, since the thin crescent Moon will set early in the evening. Note also that while the radiant of the shower is in the constellation Aquarius, meteors can appear from almost any point in the sky.

Deep Sky Objects to Look For In May Night Sky

Below are some details of three beautiful star clusters, including one in Libra and two in Scorpius:

NGC 5897

Located in Libra at a distance of about 24,000 light years (or about 40,000 light years, depending on the source consulted), this large satellite of the Milky Way is remarkable for the fact that it stretches across a distance of just over 170 light years, even though it contains only a few thousand stars. The reason for its low stellar density is not exactly clear, but many investigators believe that the cluster is far advanced in the process of dispersion seeing that based on the very low metal content of the cluster as a whole, the cluster must have formed long before the Milky Way galaxy had formed either a disc or spiral arms.

Messier 4 (M4, NGC 6121)

Messier 4
Credit: NASA and ESA

Located in Scorpius at a distance of only about 7,200 light years, Messier 4 is the closest globular star cluster to Earth. Containing several thousand stars, it has an integrated magnitude of 5.9, with the brightest stars in the cluster having magnitudes of up to 10.8. M4 is also the first cluster in which individual stars could be resolved. Note that is a result of both its closeness to Earth, and the fact that the cluster stretches across a distance of only 75 light years, which concentrates its light over a relatively small area.  Look for this 12.2 billion-year old cluster about 1.3 degrees almost due west of the bright star Antares.

Messier 80 (NGC 6093)


Also located in Scorpius, M80 is one of the Milky Way’s largest and brightest globular clusters. The cluster contains several hundred thousand stars that are packed into a sphere that is only 95 light years across, which is probably the reason why this cluster contains a significant number of blue stragglers. These are thought to be formed when relatively old stars merge, thus creating hot, blue stars that are hotter and brighter than “normal” blue stars that are at the main-sequence turn-off point for this particular cluster. Look for this particular cluster roughly mid-way between the stars Antares and Acrab.

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