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Variable star R Aquilae in the constellation Aquila is now towards the bright end of its range and currently easily visible with binoculars and small scopes. The star is a Mira type that normally fluctuates between magnitudes +5.5 and +12.0 over a period of 284 days. At it's brightest it can be glimpsed faintly with the naked eye. At it's faintest a minimum 80mm (3.1-inch) scope is required.
Algol (β Per) is a bright eclipsing binary system located in the northern constellation of Perseus and one of the best-known variable stars in the sky. Often referred to as the "Demon Star" most of the time it shines at magnitude +2.1 but every two days, 20 hours and 49 minutes the star suddenly dips in brightness to magnitude +3.4, remaining dim for about 10 hours before returning to its original state.
Why the change in brightness? The Algol system consists of at least three-stars (β Per A, β Per B and β Per C) with the orbital plane of Algol A and B directly in line with the Earth. The regular dips in brightness occur when the dimmer B star moves in front of and eclipses the brighter A star. There is also an extra dimension in that a secondary eclipse occurs when the brighter star occults the fainter secondary but this results in a very small dip in brightness that can only be detected by those with access to photo-electrical equipment.
Mercury reaches greatest elongation on June 5th when it's positioned 24.2 degrees west of the Sun. Despite this at northern latitudes the angle of the ecliptic is unfavourable and the planet will be challenging to spot low down above the eastern horizon. However it's a different story from the Southern Hemisphere where elusive Mercury puts on a respectable morning show for the first three weeks of the month. During week one it rises more than two hours before the Sun and can be seen 10 degrees above the east-northeastern horizon an hour before sunrise. After that Mercury slips back towards the Sun until it's finally lost to the bright twilight during the last week of June. It should be noted that the planet gains in brightness from mag. +0.8 to -1.0 during the visibility period.
On June 3rd, the thin waning crescent Moon passes 0.7 degrees south of Mercury (mag. +0.5) with an occultation visible from southern Africa and Madagascar (9:47 UT).
Venus reaches superior conjunction on June 6th. Since the planet is currently located on the far side of the Sun it's not suitably placed for observation. Indeed from June 5th to June 7th, Venus passes directly behind the Sun as seen from Earth. This "occultation" lasts some 46 hours and for its duration no Earth based instrument will be able to detect the planet.
At conjunction Venus and the Earth are separated by 1.74 AU (260 million kilometers or 161 million miles).
Saturn reaches opposition in Ophiuchus on June 3rd. On this day the planet is visible all night long and at its best for the year. With a declination of -20.5 degrees it's much better placed from southern and tropical locations. For example, the planet reaches at maximum altitude of 77 degrees and is visible for over 13 hours from Sydney, Australia. Whereas from New York City, it climbs just 29 degrees high, visibility only 9 hours.
The surrounding region of sky also contains Mars (mag. -2.0) about 15 degrees to the west and first magnitude red supergiant star Antares (α Sco - mag. +1.0) approx. 6 degrees southwest of Saturn. Of the three objects Mars is easily the brightest followed by Saturn then Antares. Saturn reaches its highest point in the sky at around midnight local time.
PanSTARRS (C/2013 X1) is currently the brightest comet in the sky and can be seen with binoculars and small telescopes in early morning. The comet is currently approaching Earth and will continue to brighten slightly, peaking at mag. +6.0 when closest approach is reached at the end of June. It's better placed from southern and equatorial latitudes where it appears high in the sky than from northern temperate locations where it always keeps low down.
Now is a great time for observers of Mars as the famous "Red planet" reaches opposition on May 22nd in Scorpius. On this day it peaks at mag. -2.1 and for a short time rivals the normally more brilliant Jupiter in brightness. However although visible all night long, due to its southern declination Mars is much better placed from Southern Hemisphere and tropical latitudes rather than northern temperate locations. For example on May 22nd from London, England the planet rises at 20:55 and sets at 05:02, a visibility period of about 8 hours. Whereas from Sydney, Australia it rises at 16:52 and sets at 07:00 hence visible for over 14 hours. In addition, Mars reaches a maximum altitude of just 17 degrees above the southern horizon from London. For comparison from Sydney it peaks at 77 degrees above the horizon, effectively appearing overhead.
Jupiter although fading remains a beautiful evening object in the constellation of Leo. After sunset the giant planet can be seen high in the sky above the south-western (Northern Hemisphere) or north-eastern horizon (Southern Hemisphere). It's impossible to miss Jupiter, with an apparent magnitude of -2.2 the planet is more than twice as bright as Sirius the brightest night time star. It's also brighter than all other planets except for Venus, although at the moment slightly fainter Mars does rival Jupiter in brightness. However, it's impossible to confuse the two planets. Mars rises just after sunset and is a deep orange/red in colour compared to brilliant white Jupiter which is high in the sky as soon as it's dark enough. Both planets dominate their surrounding region of sky.
On the evenings of May 14th and 15th a lovely pairing occurs when the waxing gibbous Moon passes just a couple of degrees south of Jupiter.
On May 9th a transit of Mercury occurs when the planet crosses the face of the Sun for the first since 2006. The event is visible (at least partially) from most parts of the World. It begins at 11:12 UT, ends at 18:42 UT with the midpoint occurring at 14:58 UT. The transit lasts for 7.5 hours in total and observers will notice a tiny 10 arc second diameter dark disk moving slowly across the solar face.
The annual Eta Aquariids meteor shower peaks on the morning of May 6th. For Southern Hemisphere observers this is the best meteor shower of the year. In addition, prospects are good as the New Moon won't interfere during peak activity and up to 55 meteors per hour are predicted.
The parent body for the Eta Aquariids meteor shower is Halley's comet (1P/Halley). This isn't the only annual shower associated with the famous comet, the October Orionids also originate from the same source. Although Halley has now left the inner Solar System and won't return until 2061 it's worth remembering that every Eta Aquariids meteor is actually a small part of the famous comet burning up in the Earth's atmosphere.