Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during June 2013.

Leo the Lion is in the west after sunset. Between Leo's hindmost star, Denebola, and the bright star Arcturus, in Bootes, is the constellation of Coma Berenices, which hosts part of the Virgo Galaxy Cluster. Corona Borealis, the Northern Crown, is an arclet of stars near between Bootes and Hercules. The four brightest stars in Hercules make a trapezium shape called the Keystone, and the globular cluster M13 can be found two thirds of the way up one side of it. The bright star Vega, in Lyra, is towards the east, and near to it is the Double Double - Epsilon Lyrae - which appears as a double star in binoculars but as a pair of double stars through a telescope. Cygnus the swan rises high into the sky later in the night, with its bright star Deneb. Altair, in Aquila, is lower to the south-east and completes the Summer Triangle of Vega, Deneb and Altair. About a third of the way from Altair to Vega is the dark region of the Milky Way called the Cygnus Rift, as well as the asterism called Brocchi's Cluster or the Coathanger.

The Planets

• Jupiter is still just about visible at twilight at the beginning of the month. It shines at magnitude -1.8, but is lost against the setting Sun by mid-month, after which it will re-emerge into the pre-dawn sky towards the end of July.
• Saturn is in Virgo and crosses the south as darkness falls. It is near the first-magnitude star Spica, but appears more yellow in colour. Its angular diameter decreases from 18.5 to 17.8" over the month as it moves away from us. It also approaches the star Kappa Virginis, which has a magnitude of +4.2, and is 0.5 degrees away from it at month's end. Saturn's rings are now at 17 degrees to the line of sight, allowing the largest gap between the rings, Cassini's Division, and the planet's largest moon, Titan, to be seen using a small telescope. Saturn's maximum elevation each night is now quite low, and will continue to decrease over the coming years.
• Mercury forms the top of a line with Venus and Jupiter on the 1st. It has a magnitude of -0.4, and reaches greatest eastern elongation (its furthest easterly point from the Sun in the sky) on the 12th. It is best seen at that time, being 24 degrees from the Sun, and can be most easily viewed around 30 minutes after sunset. A telescope will show its slightly gibbous disc, 8" across. Mercury is 2.1 degrees from Venus on the 18th, moving below it to 1.9 degrees' separation the following night. You made need binoculars to locate Mercury at this time, so be sure to use them only after the Sun has gone down.
• Mars reached superior conjunction (passing behind the Sun) on the 18th of April, and this month appears in the eastern sky before dawn. It rises about 30 minutes before the Sun on the 1st. It is difficult to spot at magnitude +1.4, but this becomes easier by the end of the month, when it is 7 degrees above the horizon shortly before dawn. You may still need binoculars to find it, so put them away before the Sun comes up.
• Venus is about 8 degrees above the western horizon 30 minutes after sunset at the beginning of the month. It does not get very high in the sky, reaching 10 degrees' elevation around the 20th-25th. Its disc, 10" across, is 96 percent illuminated at the star of June as it is on the far side of the Sun, shining at magnitude -3.8. By the end of the month, it is still 91 percent illuminated.

Highlights

• The asteroid Ceres can be found between the 5th and 7th, when it passes within 1 degree of the star Pollux, in Gemini. Look towards the west about an hour after sunset using binoculars to spot the asteroid at magnitude +8.8, but don't mistake it for a star of magnitude +8.4 nearby!
• Mercury, Venus and a thin crescent Moon congregate on the 10th, visible shortly after sunset if you have a low western horizon. You may also spot earthshine - sunlight reflected from the Earth and reflected again from the dark part of the Moon.
• A gibbous Moon appears very close to Spica, in Virgo, on the 18th, with Saturn not far away.

Southern Hemisphere

John Field from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during June 2013.

The south-eastern evening sky is dominated by the zodiacal constellations of Scorpius the Scorpion and Sagittarius the Archer. The red star Antares marks the Heart of the Scorpion, and its name means 'The Rival of Mars'. To Maori, and some Polynesians, Scorpius is seen as a fishing hook. Rehua is one Maori name for Antares, showing the blood of Maui staining the eye of the Hook. Straddling the Milky Way, the region around Scorpius is home to a number of nebulae and star clusters. The globular clusters M4 and NGC 6144 are near to Antares and can be observed using binoculars, while a number of double stars can be found along the body of the Scorpion. The open star cluster NGC 6231 appears rather like a comet to the naked eye and is near to the Scorpion's stinger, as is the hazier-looking open cluster M7. M6, the Butterfly Cluster, is in the same region but is fainter. Sagittarius also contains a wealth of nebulae and star clusters, while its brightest stars form the asterism known as the Teapot. Using binoculars, the globular cluster M22 can be found near to Lambda Sagitarii, which marks the top of the Teapot. M8 and M20 - otherwise known as the Lagoon Nebula and the Trifid Nebula - make spectacular sights in Sagittarius. M8 is a compact open cluster surrounded by a circle of nebulosity containing a dark rift. M20 is similar, but is distinguished by dark lanes that split the nebula into three segments. The constellation of the Archer also hosts M23, an open cluster forming arcs of stars, M24, a looser cloud of stars, M25, an open cluster containing several deep yellow stars, and M55, a globular cluster. The Milky Way is at its brightest, widest and densest around Scorpius and Sagittarius because we are looking towards the centre of our Galaxy, some 30,000 light-years away. In Arabic it is Al Nahr, the river, to the Chinese it is the River of Heaven, and to Maori it is Te Ika Roa, the Long Fish. It contains dark bands consisting of gas and dust which may eventually form new clusters of stars.

The planet Saturn is easily spotted in the northern sky after sunset, while Venus appears with Mercury in the west. The Moon will also be in the west as the Sun sets on the 10th, while Venus and Mercury will be only 2 degrees apart on the 20th. The 21st marks the winter solstice, when the Sun rises and sets at its most northerly points and the night hours are at their longest. This date was celebrated in many cultures. In Aotearoa (New Zealand), the dawn rising of Matariki (the Pleiades Cluster) and Puanga (the star Rigel) coincide with the winter solstice, and mark the beginning of the new calendar year in the Maori system known as Te Maramataka.