Night sky guide for May 2015

If not for the nearly full moon spoiling the party, southern hemisphere observers would be in for a special treat when above average meteor shower – Eta Aquarids – peaks on the night of May 5 and the morning of May 6. This meteor shower is capable of producing up to 60 meteors per hour at its peak. In northern hemisphere, the rate can reach about 30 meteors per hour.

Second meteor shower for the month of May – Alpha Scorpiid – is forecast to peak on May 13 and is expected to produce around 5 meteors per hour. The Moon will be 25 days old and will present minimal interference.

The best time of the month to observe faint objects such as galaxies and star clusters – New Moon – is scheduled for May 18.

• May 3 – C/2015 F2 (Polonia) reaches its brightest. Comet C/2015 F2 (Polonia) is forecast to reach its brightest, at around mag 9.2. It will lie at a distance of 1.21 AU from the Sun, and at a distance of 0.73 AU from the Earth. 

• May 4 – Full Moon – 03:42 UTC. The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated. This full moon was known by early Native American tribes as the Full Flower Moon because this was the time of year when spring flowers appeared in abundance. This moon has also been known as the Full Corn Planting Moon and the Milk Moon.

• May 5 – Conjunction between the Moon and Saturn – 16:26 UTC. The Moon and Saturn will make a close approach, passing within 1°58' of each other. At the moment of closest approach, the Moon will be at mag -12.6, and Saturn at mag 0.8, both in the constellation Scorpius. 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, 6 – Eta Aquarids meteor shower. The Eta Aquarids is an above average shower, capable of producing up to 60 meteors per hour at its peak. Most of the activity is seen in the southern hemisphere. In the northern hemisphere, the rate can reach about 30 meteors per hour. It is produced by dust particles left behind by comet Halley, which has known and observed since ancient times. The nearly full moon will be a big problem this year blocking out all but the brightest meteors. If you are patient, you should still be able to catch a few good ones. Best viewing will be from a dark location after midnight. Meteors will radiate from the constellation Aquarius, but can appear anywhere in the sky.

• May 7 – Mercury at greatest eastern elongation – 05:26 UTC. The planet Mercury reaches greatest eastern elongation of 21.2 degrees from the Sun. This is the best time to view Mercury since it will be at its highest point above the horizon in the evening sky. Look for the planet low in the western sky just after sunset.

• May 12 – M5 is 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 5.8, M5 is quite faint, and certainly not visible to the naked eye, but can be viewed through a pair of binoculars or small telescope.

• May 13 – Alpha Scorpiid meteor shower. The Alpha Scorpiid meteor shower will reach its maximum rate of activity on May 13, 2015. Some shooting stars associated with the shower are expected to be visible each night from April 20 to May 19. The maximum rate of meteors expected to be visible from a dark location is around 5 per hour (ZHR). The Moon will be 25 days old at the time of peak activity, and so will present minimal interference. The radiant of the  Alpha Scorpiid meteor shower is at around right ascension 16h20m, declination -24°, as shown by the green cross on the planetarium above. All of the meteors will appear to be traveling directly outward from this point, as indicated by the white lines drawn above.

• May 14 – C/2015 G2 (MASTER) reaches its brightest. Comet C/2015 G2 (MASTER) is forecast to reach its brightest, at around mag 5.5. It will lie at a distance of 0.80 AU from the Sun, and at a distance of 0.47 AU from the Earth.

• May 15 – Conjunction between the Moon and Uranus – 12:03 UTC. The Moon and Uranus will make a close approach, passing within 0°12' of each other. At the moment of closest approach, the Moon will be at mag -10.2, and Uranus at mag 5.9, both in the constellation Pisces. At closest approach, the pair will be close enough to fit comfortably within the field of view of a telescope, but will also be visible to the naked eye or a through pair of binoculars.

• May 18 – New Moon – 04:13 UTC. The Moon will located on the same side of the Earth as the Sun and will not be visible in the night sky. This is the best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere.

• May 19 – Asteroid 532 Herculina at opposition. Asteroid 532 Herculina will be well placed for observation, lying in the constellation Serpens Caput, well above the horizon for much of the night. Regardless of your location on the Earth, 532 Herculina will reach its highest point in the sky at around midnight local time. This optimal positioning occurs when it makes its closest approach to the point in the sky directly opposite to the Sun (opposition). Since the Sun reaches its greatest distance below the horizon at midnight, the point opposite to it is highest in the sky at the same time. At around the same time that 532 Herculina passes opposition, it also makes its closest approach to the Earth (perigee) making it appear at its brightest in the night sky. Even at its brightest, 532 Herculina is a faint object beyond the reach of the naked eye or binoculars, a telescope of moderate aperture and a good star chart are needed.

• May 23 – Saturn at opposition – 01:22 UTC. Saturn will be well placed for observation, in the constellation Libra. It will be visible for much of the night, reaching its highest point in the sky at around midnight local time.

• May 24 – Conjunction between the Moon and Jupiter – 04:39 UTC. The Moon and Jupiter will make a close approach, passing within 4°58' of each other. At the moment of closest approach, the Moon will be at mag -11.4, and Jupiter at mag -2.0, both in the constellation Cancer. 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 23 – C/2015 G2 (MASTER) at perihelion. Comet C/2015 G2 (MASTER) will make its closest approach to the Sun, at a distance of 0.78 AU.

• May 27 – Comet 19P/Borrelly reaches its brightest. Comet 19P/Borrelly is forecast to reach its brightest, at around mag 10.0. It will lie at a distance of 1.35 AU from the Sun, and at a distance of 2.36 AU from the Earth.

• May 28 – M4 is well placed. 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 and cannot be seen from latitudes much north of 43°N. At magnitude 5.9, M4 is quite faint, and certainly not visible to the naked eye, but can be viewed through a pair of binoculars or small telescope.

• May 29 – Comet 19P/Borrelly at perihelion. Comet 19P/Borrelly will make its closest approach to the Sun, at a distance of 1.35 AU.

Video courtesy of Hubble Space Telescope

Sources: InTheSky (Dominic Ford), SeaSky

​Featured image: Solar System Scope image for May 23, 2015. Edit: The Watchers.