Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during June 2015.

The constellation of Leo the Lion is setting in the west after sunset, with the asterism of the Sickle forming its mane and Regulus as its brightest star. The planets Jupiter and Venus are both found here later in the month. Towards the South is the Realm of the Galaxies, in Virgo and Coma Berenices, where a telescope can pick out many deep-sky objects. The bright star Arcturus, in Bootes, resides nearby. Cygnus the Swan and Lyra the Lyre are rising in the east, with Hercules in between them and Bootes. The Summer Triangle, composed of the stars Altair in Aquila, Deneb in Cygnus and Vega in Lyra, is visible. One third of the way from Altair to Vega lies the Cygnus Rift, a dark region of dust in the Milky Way, which hosts Brocchi's Cluster, also known as the Coathanger. Ursa Major is almost overhead.

The Planets

• Jupiter is still bright in the south-west at nightfall. Its brightness declines from magnitude -1.9 to -1.8 during the month, while its angular size drops from 35 to 32.5". It moves from Cancer into Leo on the 9th and heads towards Regulus. Although the current apparition is past its best, a small telescope can still show Jupiter's equatorial bands and its four Galilean moons.
• Saturn reached opposition on the 22nd of May, so it is visible in the south-east after dark and crosses the southern sky during the night. It is moving retrograde (westwards) through the eastern part of Libra, close to the fan of three stars marking the head of Scorpius the Scorpion and only 3 degrees from the double star Beta Scorpii. The planet is 18" across, and the rings span 41", tilting at 24 degrees to the line of sight. However, Saturn's low elevation, never rising above 20 degrees from the UK, makes atmospheric blurring a problem when observing it closely.
• Mercury was at inferior conjunction (between the Earth and Sun) on the 30th of May, so it is not visible for the first part of June. It then climbs slowly into the pre-dawn sky, reaching western elongation (its greatest separation from the Sun in our sky) on the 24th. It has a magnitude of +0.5 and an illuminated fraction of 35 percent at this time, and should be visible just above the east-north-eastern horizon at dawn, with Aldebaran and the Hyades Cluster 2 degrees to its lower right. By month's end, Mercury is a little brighter and sits 6 degrees above the horizon 45 minutes before sunrise.
Mars passes behind the Sun (superior conjunction) on the 14th, so it is not visible this month.
• Venus brightens from magnitude -4.4 to -4.6 this month, dominating the western sky after sunset. It reaches elongation on the 6th, when it is 45.5 degrees from the Sun in the eastern part of Gemini. At the beginnings of June, it appears about half an hour after sunset, 29 degrees above the horizon. It grows from 22 to 32" during the month, while its illuminated fraction drops from a gibbous 53 to a crescent 34 percent. It is 19 degrees above the horizon at sunset at the end of the month, setting around 23:35 BST (British Summer Time, 1 hour ahead of Universal Time) from the UK.

Highlights

• This month is a good time to observe Saturn, as it is due south and at its highest not long after dark. To find it, follow the Plough's handle downwards to the orange star Arcturus, then continue to the white star Spica in Virgo. Saturn is a little brighter and yellower than Spica, and lies to its lower left in Libra. Binoculars or a telescope should reveal Saturn's brightest moon, Titan, at magnitude +8.2, and a magnification of at least 25 times allows the planet's rings to be seen. Saturn is visibly flattened by its rapid rotation. It has bands on its surface, but their colours are muted. The outer A and B rings are separated by Cassini's Division, which should be visible in a telescope of 4 or more inches (10 centimetres) in aperture when the atmosphere is fairly still. Within them is the C ring, but this is harder to spot. The inclination of the rings increases with respect to Earth until May 2017, making them more visible than usual for the next few years.
• The globular cluster M13 in Hercules and the 'Double Double' in Lyra are easily seen with binoculars or a telescope this month. M13 appears as a fuzzy blob, and is the brightest globular cluster in the northern hemisphere sky. The Double Double consists of a pair of binary stars to the lower left of Vega, which looks like two stars in binoculars but four in a telescope.
• The latter part of June is a good time to spot noctilucent (or polar mesospheric) clouds. Seen in the north at the end of twilight, they are the highest clouds in our atmosphere and float some 50 miles (80 kilometres) above the ground. Normally too faint to see, they can appear when illuminated by the Sun a little while after it has dropped below the horizon as seen from the ground. Look for them on a dark, clear night, as the last daylight is draining from the northern sky.
• The June Lyrid meteor shower peaks on the night of the 15th-16th. The meteors appear to radiate from a point near the star Vega in Lyra. Although there will be probably be only about 8 visible meteors per hour, the very thin crescent Moon does not obscure viewing.
• Venus lies close to the Beehive Cluster (M44) in Cancer on the 12th and 13th.
• The waxing gibbous Moon passes close to Saturn after sunset on the 28th. They are just over 1 degree apart when they set around 02:30 BST on the 29th.
• Venus and Jupiter, the two brightest objects currently in the night sky apart from the Moon, are just 21' apart on the 30th. Both are moving eastwards, with Venus catching up while the two are approaching the star Regulus in Leo. The planets have similar angular diameters at this time, around 32" each, but Venus is a crescent while Jupiter, because it is much further from the Sun than is the Earth, appears almost full. Though low in the west-north-west, they are very noticeable for about an hour from 22:30 BST.

Southern Hemisphere

Claire Bretherton from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during June 2015.

The winter solstice occurs on the 22nd (New Zealand Standard Time or NZST, 12 hours ahead of Universal Time) of this month, when the southern hemisphere is at its greatest tilt away from the Sun and the hours of daylight are at their shortest. The word 'solstice' indicates that the Sun is still, because it rises and sets at its most northerly points before moving south again. Brilliant Venus and golden Jupiter appear in the north-west after sunset, getting closer together as Venus ascends and Jupiter descends in the sky. They are joined by the crescent Moon on the 20th, and by the end of the month the two planets are less than one Moon diameter apart.

The centre of the Milky Way, in the constellation of Scorpius, rises high in the sky when seen from the southern hemisphere, and is currently midway up the eastern sky in the evening. The winter constellations of Scorpius and Sagittarius will dominate the night sky over the next few months. The red giant star Antares marks the heart of Scorpius, the Scorpion, and a near-vertical line of stars to its left represents the Claws. Saturn, at magnitude +0.8, is a little further left still, with an almost-full Moon passing within 1.5 degrees of it on the 2nd. Scorpius is known to Maori as Te Matau a Maui, the Fish-hook of Maui. The mythical figure Maui used this to pull a giant fish from the ocean, which became Te Ika-a-Maui, the North Island of New Zealand. Antares is called Rehua, representing a drop of blood from Maui's nose that he used as bait. Scorpius was an important navigation aid in the South Pacific, as it moves overhead and shows the directions of east and west that would bring sailors to Aoteroa (New Zealand). Below the Fish-hook, the brightest stars of Sagittarius make the shape of an upside-down Teapot, and many star clusters and nebulae line the Milky Way in this part of the sky. M7, an open star cluster visible to the naked eye, sits about halfway between the stinger of the Scorpion and the spout of the Teapot. The nearby Butterfly Cluster, M6, is a lovely sight in binoculars.

The Maori new year, Matariki, happens this month when the Pleiades star cluster, also called Matariki, rises at dawn. Scorpius is on the west-south-western horizon at this time of year, with the Fish-hook pointing upwards, and Orion the Hunter is on the opposite side of the sky, rising due east. The three stars of Orion's Belt, known as Tautoru, line the horizon, and point to Sirius on their right. Sirius is called Takarua, and is the brightest night-time star. Following the Belt left leads to the V-shaped head of Taurus the Bull, with the orange star Aldebaran marking his Eye, and then to Matariki as it rises in the east-north-east. The Pleiades disappear from the sky in April, and their reappearance in early June indicates that the new year is approaching, with the next New Moon (or, in some areas, the next Full Moon) marking the actual turn of the year. This month, the New Moon happens on the 17th. Matariki, Tautoru, Takarua and Rehua are the four points of a celestial compass used to navigate the Pacific Ocean, with Matariki and Takarua marking the extremities of the Sun's rising points, Tautoru placed at one end of the celestial equator (the star Altair being at the other) and the Sun and planets moving along the line between Matariki and Rehua. They are also the four pillars, or Pou, holding up the Sky Father, Ranginui or Rangi, in Maori lore.