Night Sky Guide for May 2019

May 2 – Conjunction of the Moon and Venus – 11:41 UTC. The Moon and Venus will share the same right ascension, with the Moon passing 3°37' to the south of Venus. The Moon will be 27 days old. The Moon will be at mag -9.6 in the constellation Cetus, and Venus at mag -3.9 in the neighboring constellation of Pisces. The pair will be too widely separated to fit within the field of view of a telescope but will be visible to the naked eye or through a pair of binoculars.

May 2 – C/2017 M4 (ATLAS) reaches its brightest. Comet C/2017 M4 (ATLAS) is forecast to reach its brightest, at around mag 12.8. It will lie at a distance of 3.41 AU from the Sun, and at a distance of 2.52 AU from the Earth.

May 3 – Conjunction of the Moon and Mercury – 06:27 UTC. The Moon and Mercury will share the same right ascension, with the Moon passing 2°54' to the south of Mercury. The Moon, 28 days long, will be at mag -8.8, and Mercury at mag -0.5, both in the constellation Pisces. The pair will be too widely separated to fit within the field of view of a telescope but will be visible to the naked eye or through a pair of binoculars.

May 5 – New Moon – 22:47 UTC. The Moon will pass close to the Sun and become lost in the Sun's glare for a few days. The Moon's orbital motion carries it around the Earth once every four weeks, and as a result, its phases cycle from the new moon, through the first quarter, full moon and last quarter, back to new moon once every 29.5 days. At new moon, the Earth, Moon, and Sun all lie in a roughly straight line, with the Moon in the middle, appearing in front of the Sun's glare. In this configuration, we see almost exactly the opposite half of the Moon to that which is illuminated by the Sun, making it doubly unobservable because the side we see is unilluminated. Over coming days, the Moon will rise and set an hour later each day, becoming visible in the late afternoon and dusk sky as a waxing crescent which sets soon after the Sun. By the first quarter, in a week's time, it will be visible until around midnight.

May 6 – η–Aquarid meteor shower. The η–Aquarid meteor shower will reach its maximum rate of activity on May 6 but some shooting stars associated with the shower are visible each night from April 24 to May 20. Annual meteor showers arise when the Earth passes through streams of debris left behind by comets and asteroids. As pebble-sized pieces of debris collide with the Earth, they burn up at an altitude of around 70 to 100 km (45 – 62 miles), appearing as shooting stars. By determining the speed and direction at which the meteors impact the Earth, it is possible to work out the path of the stream through the Solar System and identify the body responsible for creating it. The parent body responsible for creating the η–Aquarid shower is Halley's Comet.

May 8 – Conjunction of the Moon and Mars – 23:36 UTC. The Moon and Mars will share the same right ascension, with the Moon passing 3°14' to the south of Mars. The Moon will be 3 days old. At around the same time, the two objects will also make a close approach, technically called an appulse. The Moon will be at mag -10.2, and Mars at mag 1.7, both in the constellation Taurus. The pair will be too widely separated to fit within the field of view of a telescope but will be visible to the naked eye or through a pair of binoculars.

May 8 – Close approach of the Moon and Mars – 00:21 UTC. The Moon and Mars will make a close approach, passing within 3°12' of each other. The Moon will be at mag -10.2, and Mars at mag 1.7, both in the constellation Taurus. The pair will be too widely separated to fit within the field of view of a telescope but will be visible to the naked eye or through a pair of binoculars. At around the same time, the two objects will also share the same right ascension – called conjunction.

May 8 – Conjunction of Mercury and Uranus – 08:09 UTC. Mercury and Uranus will share the same right ascension, with Mercury passing 1°22' to the south of Uranus. Mercury will be at mag -0.8, and Uranus at mag 5.9, both in the constellation Aries. The pair will be too widely separated to fit within the field of view of a telescope but will be visible through a pair of binoculars.

May 11 – Close approach of the Moon and M44 – 02:15 UTC. The Moon and M44 will make a close approach, passing within 0°19' of each other. The Moon will be at mag -11.7, and M44 at mag 3.1, both in the constellation Cancer. The pair will be close enough to fit within the field of view of a telescope, but will also be visible through a pair of binoculars.

May 12 – Moon at First Quarter – 01:14 UTC. The Moon will be prominent in the evening sky, setting around midnight. At this time in its monthly cycle of phases, it appears almost exactly half illuminated.

May 12 – Asteroid 8 Flora at opposition – 04:48 UTC. Asteroid 8 Flora will be well placed for observation, lying in the constellation Libra, well above the horizon for much of the night. Regardless of your location on the Earth, 8 Flora will reach its highest point in the sky at around midnight local time.

May 12 – M5 well placed for observation. The globular cluster M5 (NGC 5904) in Serpens will be well placed for observation. It will reach its highest point in the sky at around midnight local time. At a declination of +02°04', it is visible across much of the world; it can be seen at latitudes between 72°N and 67°S. At magnitude 5.7, M5 is too faint to be seen with the naked eye from any but the very darkest sites but is visible through a pair of binoculars or a small telescope.

May 13 – α–Scorpiid meteor shower. The α–Scorpiid meteor shower will reach its maximum rate of activity on May 13 but some shooting stars associated with the shower are visible each night from April 20 to May 19. The parent body responsible for creating the α–Scorpiid shower has been tentatively identified as 2004 BZ74.

May 14 – Asteroid 11 Parthenope at opposition – 16:48 UTC. Asteroid 11 Parthenope will be well placed for observation, lying in the constellation Libra, well above the horizon for much of the night. Regardless of your location on the Earth, 11 Parthenope will reach its highest point in the sky at around midnight local time.

May 18 – Conjunction of Venus and Uranus – 08:08 UTC. Venus and Uranus will share the same right ascension, with Venus passing 1°09' to the south of Uranus. Venus will be at mag -3.9, and Uranus at mag 5.9, both in the constellation Aries. The pair will be too widely separated to fit within the field of view of a telescope but will be visible through a pair of binoculars.

May 18 – Full Moon – Blue Moon – 21:13 UTC. The Moon will reach full phase at 21:13 UTC on May 18. At this time in its monthly cycle of phases, the Moon lies almost directly opposite the Sun in the sky, placing it high above the horizon for much of the night. The sequence of full moons through the year are often assigned names according to the seasons in which they fall. This month's is assigned the unusual name of a blue moon. Blue moons come about as a result of a quirk in the way that full moons are counted. Usually, only three fall within any each of the Earth's season which last an average of three months. A sequence of three traditional names are given in turn to these three full moons. However, occasionally, a fourth full moon can fall within a single season. This happens because full moons recur every 29.53 days, and so the Moon's phases cycle on average 12.37 times each year, or 3.11 times each season. As a result, there will be four full moons within a season once every 2.7 years. When this happens, there are only three traditional names to go between four full moons, and so the third of them is called a blue moon instead.

May 20 – Asteroid 20 Massalia at opposition – 16:48 UTC. Asteroid 20 Massalia will be well placed for observation, lying in the constellation Libra, well above the horizon for much of the night. Regardless of your location on the Earth, 20 Massalia will reach its highest point in the sky at around midnight local time.

May 20 – Conjunction of the Moon and Jupiter – 16:54 UTC. The Moon and Jupiter will share the same right ascension, with the Moon passing 1°41' to the north of Jupiter. The Moon will be 16 days old. At around the same time, the two objects will also make a close approach, technically called an appulse. The Moon will be at mag -12.6, and Jupiter at mag -2.6, both in the constellation Ophiuchus. The pair will be too widely separated to fit within the field of view of a telescope but will be visible to the naked eye or through a pair of binoculars.

May 20 – Close approach of the Moon and Jupiter – 17:20 UTC. The Moon and Jupiter will make a close approach, passing within 1°40' of each other. The Moon will be 16 days old. The Moon will be at mag -12.6, and Jupiter at mag -2.6, both in the constellation Ophiuchus. The pair will be too widely separated to fit within the field of view of a telescope but will be visible to the naked eye or through a pair of binoculars. At around the same time, the two objects will also share the same right ascension – conjunction.

May 21 – Mercury at superior solar conjunction – 12:55 UTC. Mercury will pass very close to the Sun in the sky as its orbit carries it around the far side of the solar system from the Earth. This occurs once in every synodic cycle of the planet (116 days), and marks the end of Mercury's apparition in the morning sky and its transition to become an evening object over the next few weeks. At closest approach, Mercury will appear at a separation of only 0°19' from the Sun, making it totally unobservable for several weeks while it is lost in the Sun's glare. Mercury will also pass apogee – the time when it is most distant from the Earth – at around the same time since it will lie exactly opposite to the Earth in the Solar System. It will move to a distance of 1.32 AU from the Earth, making it appear small and very distant. If it could be observed, it would measure 5.1 arcsec in diameter, whilst appearing completely illuminated.

May 23 – Conjunction of the Moon and Saturn – 22:14 UTC. The Moon and Saturn will share the same right ascension, with the Moon passing 0°31' to the south of Saturn. The Moon will be 18 days old. At around the same time, the two objects will also make a close approach, technically called an appulse. The Moon will be at mag -12.4, and Saturn at mag 0.2, both in the constellation Sagittarius. The pair will be a little too widely separated to fit comfortably within the field of view of a telescope but will be visible to the naked eye or through a pair of binoculars.

May 23 – Close approach of the Moon and Saturn – 22:18 UTC. The Moon and Saturn will make a close approach, passing within 0°31' of each other. The Moon will be at mag -12.4, and Saturn at mag 0.2, both in the constellation Sagittarius. The pair will be a little too widely separated to fit comfortably within the field of view of a telescope but will be visible to the naked eye or through a pair of binoculars. At around the same time, the two objects will also share the same right ascension – conjunction.

May 23 – Close approach of the Moon and Pluto – 03:57 UTC. The Moon and 134340 Pluto will make a close approach, passing within 0°04' of each other. The Moon will be 19 days old. The Moon will be at mag -12.3, and 134340 Pluto at mag 14.7, both in the constellation Sagittarius. The pair will be close enough to fit within the field of view of a telescope, but will also be visible through a pair of binoculars.

May 26 – Moon at Last Quarter – 16:35 UTC. The Moon will be prominent in the dawn sky, rising at around midnight.

May 28 – M4 well placed for observation. Across much of the world, the globular cluster M4 (NGC 6121) in Scorpius will be well placed for observation. It will reach its highest point in the sky at around midnight local time. At a declination of -26°31', it is easiest to see from the southern hemisphere but cannot be seen from latitudes much north of 43°N. At magnitude 5.4, M4 is too faint to be seen with the naked eye from any but the very darkest sites but is visible through a pair of binoculars or a small telescope.

May 29 – 1 Ceres at opposition – 01:35 UTC. 1 Ceres will be well placed for observation, in the constellation Ophiuchus. It will be visible for much of the night, reaching its highest point in the sky at around midnight local time.

Sources: In The Sky by Dominic Ford, NASA, TW

Featured image credit: Hubble