August 20, 2019

Astro event of the Week, August 12-18, 2008: See a Triple Conjunction!

Alas, poor North America! We miss out of both this months’ eclipses! But I give you as an Astro consolation of sorts; a rare triple planetary conjunction!

On the evening of August, 15th, the planets Mercury, Venus, and Saturn will span an area of less than 2 degrees, a nice binocular view. Look low to the west, about a half hour after sunset. Venus will be easy to spot with the naked eye, while Mercury will be more difficult. Ironically, the largest of the trio, Saturn, will be toughest to spot! Binocs may aid with this one… that’s because Saturn is currently at a distance of 10.3 AUs, while Mercury and Venus are only 1.3 and 1.6 AUs away, respectively. See a faint point off to the far left? That’s Mars, currently receding from us, on the far side of the sun.

And that brings us to the Astro-word of the week, which is Magnitude.  Apparent magnitude is the visual brightness of an astronomical object, usually a star or planet. The lower the number value, the brighter the object. The original scale devised by the Greeks simply ranked six classifications of stars, “1″ being the brightest and “6″ being the faintest visible to the naked eye. In 1856, the scale was standardized, fixing a 1st magnitude star as 100 times brighter than a 6th magnitude star. This makes the scale logarithmic, meaning the difference between increments is an order of x2.512. Polaris, and later Vega, was used to “fix” the scale, Vega being assigned a magnitude of 0.0.   During this weeks’ triple conjunction, Venus will be magnitude -3.8, Mercury -1.2, and Saturn a faint +0.8.

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