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For those living at equatorial and southern latitudes comet Catalina (C/2013 US10) is now visible as an evening object with binoculars or small telescopes. When discovered by R. A. Kowalski of the Catalina Sky Survey on Halloween night 2013 it was incredibly faint (mag. +18.6). At the beginning of August 2015 it had brightened significantly to magnitude +7.4 and although still not bright enough to be seen with the naked eye, it's easy with binoculars and small telescopes, appearing as an obvious non-stellar fuzzy "star".
Neptune the eighth planet from the Sun and most distant in the Solar System reaches opposition in Aquarius on September 1, 2015. On this day it will be 28.9533 AU (approx. 4331.4 million km or 2690.6 million miles) from Earth and visible all night, rising above the eastern horizon at sunset and then setting in the west as the Sun reappears.
Shining at magnitude +7.8, Neptune is the only planet that's never visible to the naked eye - although Uranus requires dark skies to be glimpsed. However provided you know exactly where to look, Neptune is a relatively easy to find with binoculars or small telescopes.
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) and from our perspective the orbital plane of Algol A and Algol B is in the 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 a secondary eclipse when the brighter star occults the fainter secondary but this results in a very small dip in brightness that can only be detected photoelectrically.
Saturn, mag. +0.4, remains well placed for observation amongst the stars of Libra during August. The beautiful ringed planet has just resumed direct motion once more and is visible as soon as it's dark towards the southwest (Northern Hemisphere) / northeast (Southern Hemisphere) before setting around or just after midnight. With a declination of -17 degrees it's better situated from southerly latitudes, appearing higher in the sky.
At the start of August from southern and tropical latitudes the planets Mercury, Venus and Jupiter are all visible low down above the western horizon just after sunset. The brightest planet is Venus (mag. -4.1) followed by Jupiter (mag. -1.7) with Mercury the faintest (mag. -0.6). During the first 10 days of the month the three planets will "dance" above the horizon, offering a slightly different view each subsequent evening. After this, Venus and Jupiter will be lost to the bright twilight sky but Mercury will improve in altitude for some days, remaining visible well into September.
The diagram below shows the evening apparition of Mercury, Venus and Jupiter from Sydney, Australia at latitude 35S. Positions are displayed 45 minutes after sunset. Note the position of the planets will be slightly different when viewed from varying southern or tropical latitudes / longitudes.
Chi Cygni is a long period variable star that returns to peak brightness during early to middle August 2015. Already the star has reached naked eye brightness; at the beginning of the month it hit magnitude +5.0 and with a more days to go before maximum it's expected to brighten to at least magnitude +4.0.
What makes Chi Cyg fascinating is that it's a Mira type variable with an extremely large brightness range. Mira type stars are pulsating red giants that vary by at least one magnitude over periods ranging from 80 to over 1,000 day's. These stars are coming to the end of their lives and will eventually form a planetary nebula with a white dwarf at the centre. There are at least 6,000 known Mira type stars.
Chi Cyg is the second brightest Mira star (after Mira - omicron Ceti) and has been known to brighten up to magnitude +3.3 and fade down to magnitude +14.2 over a period of 407 days. However every cycle is different. Often the star is visible to the naked eye at brightest but not always. For example, the 2014 maximum was one of the faintest on record at magnitude +6.5. At the opposite end of the scale Chi Cyg can dip down to about as faint as dwarf planet Pluto, hence requiring at least a 250mm (10-inch) scope to be spotted!
The Perseids one of the finest annual meteor showers peaks this year on the night of August 12th/13th. On this date up to 100 meteors per hour can be seen under perfect conditions. This years event promises to be a good one as the New Moon won't interfere at all.
Recent analysis by NASA has rated the Perseids as the best meteor shower when it comes to fireballs. The shower is also extremely reliable, it rarely fails to deliver and has been observed for over 2000 years. Of all other annual showers only the December Geminids is comparable.
Mercury reaches greatest eastern elongation on September 4th and apart from the first few days is visible as an "evening star" throughout August from the tropics and Southern Hemisphere. This also happens to be their most favourable evening apparition of 2015, representing the best chance to catch a glimpse of this small world after sunset. Unfortunately, from northern temperate latitudes the angle of the ecliptic is unfavourable and the planet remains low down and unsuitably placed for observation throughout the month.
Observers located at equatorial and southern latitudes have the chance to spot a reasonably bright comet after sunset during the second half of July and into August. The comet named PanSTARRS (C/2014 Q1) is now fading but should remain bright enough to be visible with binoculars and small telescopes for sometime to come. Unfortunately, for Northern based observers it's not observable.
Comet PanSTARRS was discovered on August 16, 2014 using the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) located on the island of Maui in Hawaii. At discovery the comet shone at a feeble magnitude +18.4.