Tuesday, April 22, 2014

Zodiacal Light: Oft Ignored Astronomical Phenomena?

Even though it seems to longer register in the consciousness of most amateur astronomers, are they missing out on observing one of the most interesting astronomical phenomena?

By: Ringo Bones 

Although no prominent astronomers – amateur or otherwise – had been recently talking about it, are first time amateur astronomers missing out one of the most interesting astronomical phenomena that can even be seen by the naked eye. But why does it ever seldom if ever even mentioned at all?

The zodiacal light or the zodiacal band is a faint glow of light seen along the ecliptic just after sunset or before sunrise is another manifestation of the interplanetary meteoric material. This “zodiacal light” is caused by the reflection of sunlight from the meteoric grains moving in interplanetary space. A still fainter diffuse luminous spot called the gegenschein or “counter glow”, found directly opposite the sun in the sky and the false “F corona” of the sun seen during total eclipse are the two other phenomena caused by this interplanetary material. Although such material is slowly spiraling into the sun, it is continually replenished by the destruction of comets.  

The zodiacal light appears as a large, faint pyramidal glow whose base is the horizon after the twilight glow has faded. This form is best seen on spring evenings and mornings in October. A fainter incarnation of zodiacal light stretches clear across the sky along the ecliptic – as in the orange line in our sky maps. Because urban light pollution overpower the glow, the vast majority of amateur astronomers will only get a chance to see the zodiacal band at a star party located at a rural location devoid of most urban light pollution – where the skies are usually quite dark - as in Class 1 to Class 4 - in the Bortle Dark Sky scale. Though urban regions that register as Class 5 in the Bortle Dark Sky scale will provide adequate Zodiacal Light observations for non demanding amateur astronomers. 

Observing the zodiacal band is one of those funny things. You don’t generally notice it until someone points it out, then – under a dark sky – it is fairly straightforward to see. Keep in mind that the zodiacal light is a magnitude or two fainter than the Milky Way.

One way to detect the zodiacal band is to watch for the sky background brightness to change as you slowly scan up from the horizon. Initially you’ll see a brighter horizon haze followed by darkness, then the sky will brighten a bit – this is the zodiacal band – only o fade as you look higher. You might have to block the light from Jupiter with your hand – it’s that dim.

Once you recognize this faint belt, you’ll notice that Saturn clearly lies beneath it as shown on the Path of the Planets map if you are on the northern hemisphere.

Monday, April 21, 2014

John Bevis: The Greatest Forgotten Amateur Astronomer?

His “popularity” may have last peaked during the middle of the 1990s, but does anyone this day and age still remember John Bevis – probably England’s greatest amateur astronomer? 

By: Ringo Bones 

Amateur astronomers who had spent enough time in the library doing old school style research will probably associate amateur astronomer John Bevis with the discovery of the Crab Nebula in 1731 and his observations on an occultation by the planet Venus of Mercury back in May 28, 1737. But does his name still register in the overall consciousness of today’s amateur astronomical community?
Though he probably gained a “brief” peak in popularity during the mid 1990s in lieu of Mike Judge’s Beavis and Butt-Head on the MTV Channel, John Bevis would have been both forgotten and relegated into the dustbin of history had it been for the “old school” researcher repeatedly uncovering his “Ghost Book of Manchester” since the 1980s. Born in old Sarum Witshire back in November 10, 1695, John Bevis was more well-known as a doctor in his hometown than as an accomplished astronomer before passing away back in November 6, 1771. 

And given the mainstream press attention of the dramatic Shoemaker-Levy 9 comet impact on the surface of the planet Jupiter back in July 16, 1994 and the subsequent Hollywood’s interest in the possibility of comets and gigantic asteroids hitting the planet earth causing an extinction level event – it made two box office grossing movies during the latter half of the 1990s as in Deep Impact and Armageddon – and not to mention that the mainstream press recently found out there are more people manning America’s fast food industry than looking at the skies for comets and asteroids that might wreck havoc on earth, it has become a cause célèbre back then to “empower” the amateur astronomer so they might become joint partners of NASA’s Spaceguard Survey given the results of the 1992 Spaceguard Report and the 1995 Shoemaker Committee Report. 

London physician John Bevis would only had been remembered as a good doctor – instead of an accomplished amateur astronomer – had his plans to publish a very extensive star atlas more detailed than anything ever published before had destined to failure. In 1738, Bevis erected a private observatory at Stoke Newington on the outskirts of London where he began an ambitious project – the compilation of a star atlas that was to contain many more stars than Johann Bayer’s Uranometria of 1603 and to have greater exactness. The final product was to be Bevis’ Uranographia Britannica, an atlas of 51 charts to be accompanied by a catalog of star positions. 

Given the high cost of publishing at the time, John Bevis started to look for patrons and subscribers to cover the cost of publishing his Uranographia Britannica. Bevis collected more than 180 subscriptions and the plates are beautifully engraved each having a dedication to the particular individual or learned society in the United Kingdom and across Europe that had subscribed to the work. The first mention of the Uranographia is in a letter Bevis sent to Nicolas Louis de Lacaille in 1748, promising to send him a copy as a present. Despite of famous royal patrons at the time – like Frederick Louis, Prince of Wales – Bevis’ Uranographia Britannica wind up being proverbially called as a “Ghost Book of Manchester” and might sent Bevis to ignominious historical obscurity. 

John Bevis was rescued from ultimate “historical obscurity” back in 1981 when William B. Ashworth Jr. of the University of Missouri in Kansas City published a paper entitled “John Bevis and his Uranographia (ca. 1750).” The paper which appeared in the February 1981 Proceedings of the American Philosophical Society contained both a description and a critique of the work, which seems to describe the very atlas.  Until William B. Ashworth Jr. published his paper in 1981, Bevis’ star atlas had been largely forgotten by the scientific community. And thanks to the November 1997 research by the Manchester Astronomical Society for mid to late 18th Century “ghost books”, Kevin Kilburn, Michael Oates and Anthony Cross finally unearthed a filed copy of Bevis’ atlas in the Manchester Astronomical Society’s library back in November 12, 1997. The atlas consists of the elaborate frontispiece, 51 star charts, the advertising broadsheet and an index. Thus the Manchester copy is one of the most complete and best preserved of the 1786 “ghost book”.