31 Oct 2015

Venus, Moon, Mars and Jupiter conjunction – Record by Viv Wilson

Viv Wilson was out looking at the night sky again recently as on 8 & 9 October there was a fascinating and changing array between three planets, a bright star and a waning crescent moon in the eastern sky. On the morning of 8 October a slender crescent moon — and 5 or 6 degrees to its lower left a dazzling Venus, the queen of the dawn, and the much fainter Regulus, the brightest star of Leo. On the morning of 9 October, a thinner lunar crescent formed an isosceles triangle; the vertex angle is at Mars, while Jupiter and the moon form the base angles with Jupiter to the lower left of the moon. The Mars-Jupiter and Mars-moon sides (the "legs") measure 4 degrees long, while the base formed by Jupiter and the moon measure 6 degrees. Also on 9 October, Venus was in conjunction with Regulus, passing 2.5 degrees south of it, below and to the right, and appears nearly 230 times brighter than the bluish star. Viv has kindly given me permission to use his photos of the event which are shown below. Viv also sent me the following: There are five planets that can be seen during Oct. Venus, Jupiter, Mars and Mercury in the morning and Saturn at Night. My photo has the Moon, Venus, Jupiter and Mars. Towards the end of this month, Venus, Mars and Jupiter will meet up to present the closest grouping of planets until Jan 2021. Mars and Jupiter are currently within half a degree of each other, about the moon’s width between them. Venus, Mag -4.6 is the 3rd brightest object in the sky, following the sun, Mag -27 and the full moon, -13. Jupiter Mag-1.8, Mars Mag +1.7 and Mercury Mag -0.9. The star Vega is Mag 0. The brightness is called Magnitude and was a concept developed by the Greek astronomer, Hipparchus, 190-120 BC. By measuring and comparing the brightness of stars he made a catalogue of 850 stars, positions and comparable brightness, with the brightest star being 1 and at that time the faintest being 6. When telescopes came along in the early 1600’s, fainter stars could now be observed, so the Magnitude table required extending. In the 1900’s, the development of visual photo photometer’s, which were instruments to measure Stella intensities. This prompted Astronomers to adopt an international standard for Magnitude. Apparent Magnitude is a visual difference in brightness, Where Absolute Magnitude is the apparent magnitude an object would have, if it were located 10 parsecs from earth. The sun would go from Apparent Magnitude of -27 to Absolute Magnitude of +4.7, about as bright as Ganymede, a moon of Jupiter. Absolute Magnitudes requires lots of math’s to work it out….

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