April 19, 2019

Astro Event: A South Pacific Eclipse.

This year’s big ticket astronomical event occurs over a sparsely populated but beautiful track of our planet; we’re talking about July 11th’s total solar eclipse. Of course, it isn’t often that an eclipse doesn’t occur over the windswept Arctic or a war-torn banana republic… the Sun and sand of an island eclipse may just be the perfect combo. If you haven’t already made plans to catch one of the numerous cruises headed that way you may have to enjoy it vicariously with the rest of us via the Internet; this eclipse graces only a smattering of islands before making a brief landfall in South America across the Chilean-Argentine border at sunset. The path of solar totality will not grace our planet again until November 2012 in another South Pacific eclipse that intersects this month’s path! Its maximum length of 5 minutes and 20 seconds occurs over open ocean. Two very interesting sites for viewing include Easter Island and just off of the coast of French Polynesia and Tahiti; the more adventurous may want to head for the Cook Islands site of Mangaia, which lies right along the centerline. Weather prospects may favor the northern hump of the path, with a mean cloudiness of less than 50%… but for sheer beauty and landscape photo ops, Easter island will be your best bet. No doubt most of humanity will experience this one vicariously via the web; follow @Astroguyz via Twitter, as we’ll post where online to watch this extra-ordinary event in the days leading up to the eclipse!

The Astro-term for this week is Metonic Series. A metonic series of eclipses arises from the fact that the period of 19 tropical solar years is very nearly equal to 235 synodic months. This was first recognized by the astronomer Meton of Athens in the year 432 B.C. The error of difference is 2 hours per 19 years, and this accumulates to a full calendar day every 219 years. A metonic cycle of eclipses will share the same calendar date in groupings of 4 to 5 per series… for example, the first eclipse related to this month’s was on July 11th, 1953 and the last will be 19 years from now, on July 11, 2029. Do not confuse metonic series with saros cycle, which is independent of the solar calendar and based on a period of 223 synodic months. So what, you say? Well, metonic series not only factor into eclipses landing on the same date, but also play a role in calculating when the Moon will appear at the same phase in the same position again… metonic series even play in to trajectory calculations for lunar bound spacecraft, as well as serving as a basis for the Hebrew calendar and the computation of Easter!

07.06.10: Mega-Scope Site Selected.

The dawn of the mega-scopes is almost upon us… earlier last month, the European Southern Observatory (ESO) consortium announced a site selection for their whopping 42 meter monster; the E-ELT (European Extremely Large Telescope) which will be perched atop Cerro Armazones in central Chile. The 10,020 foot high summit beat out four other possible sites in Chile and the Canary Islands during the long site evaluation process due to its outstanding clarity and seeing. First light is projected to be 2018, and the E-ELT will be composed of a 1,000 hexagonal mirror segments bringing light to focus on a Nasmyth instrument platform.  While designers had to “settle” from designs that included scopes as large as the proposed 100-meter Overwhelmingly Large telescope (!) The E-ELT will still be four times as large as most single aperture scopes in use today. To give you an idea of its scale, the secondary mirror will be larger than the legendary Hale Telescope’s 200-inch primary! Such an engineering project will also pose crucial challenges to designers, as well as kick the “aperture envy” up among astronomers a notch…and like most new instruments, E-ELT will be able to probe the near-infrared as well as the optical. With a billion Euro sticker price, the E-ELT is sure to be one of the engineering feats of our time!