Equinox Sky Camp— Trips / Events Ideas for trips and events always welcome! events@weymouthastronomy.co.uk  16 Mar THS - "Einstein's Universe" Professor Brian Foster and Violinist Jack Liebeck  7 Apr WAS— Communications Satellites, the history— Alan Jeffries  10 Apr CADAS—One Small Step: A Celebration of Apollo - Neil Haggath  5 May WAS— Where ThisExtraterrestrials: includes free evethey? - Len Telford ningareviewing. Doors  8 May CADAS—”Title t.b.d.” by Paul Money Sky Watcher WAC News Welcome to the 100th issue of the Sky Watcher. Quite a milestone in the history of the WAC. A big thank you to all the contributors over the past issues. Looking forward to all the new material to come [hint]. Send in your photos, sketches, articles, puzzles etc... We would love to see them. Until next month...clear skies! ~SK Interesting web find of the month: How the Sloan Digital Sky Survey uses light to measure distances to galaxies. http://blog.sdss3.org/2015/02/27/howsdss-uses-light-to-measure-the-distances-togalaxies/ The heavyweight champion of the Cosmos! By Dr. Ethan  2 June WAS—Exhibition Evening Siegel  12 June CADAS—AGM and Social Evening As crazy as it once seemed, we once assumed that the Earth was the largest thing in all the universe. 2,500 years ago, the Greek philosopher Anaxagoras was ridiculed for suggesting that the Sun might be even larger than the Peloponnesus peninsula, about 16% of modern-day Greece. Today, we know that planets are dwarfed by stars, which themselves are bound together by the billions or even trillions into galaxies.  7 July WAS—Impacts! James Fradgley More to come! If you are interested in giving a talk or workshop, let the organisers know. They like to offer new titles in their programme line-up. WAC Upcoming Events: 10 Apr—Ask the Experts 8 May—(AGM) Visit to SALT Observatory—Paul Spurr 12 June—Eclipses I have known—Chris Bowden 10 July—Astrophotography— John Gifford More to come! Plans for informal viewing nights will take place after the monthly meetings, weather permitting. Volume 9, Issue 10 13 March 2015 But gravitationally bound structures extend far beyond galaxies, which themselves can bind together into massive clusters across the cosmos. While dark energy may be driving most galaxy clusters apart from one another, preventing our local group from falling into the Virgo Cluster, for example, on occasion, huge galaxy clusters can merge, forming the largest gravitationally bound structures in the universe. the El Gordo cluster has an estimated mass of 3 × 1015 solar masses, or 3,000 times as much as our own galaxy! The way we've figured this out is fascinating. By seeing how the shapes of background galaxies are distorted into more ellipticalthan average shapes along a particular set of axes, we can reconstruct how much mass is present in the cluster: a phenomenon known as weak gravitational lensing. That reconstruction is shown in blue, but doesn't match up with where the X-rays are, which are shown in pink! This is because, when galaxy clusters collide, the neutral gas inside heats up to emit X-rays, but the individual galaxies (mostly) Take the "El Gordo" galaxy cluster, catalogued as ACT-CL J0102-4915. It’s the largest known galaxy cluster in the distant universe. A galaxy like the Milky Way might contain a few hundred billion stars and up to just over a trillion (1012) solar masses worth of matter, www.weymouthastronomy.co.uk Page 2 Sky Watcher Volume 9, Issue 10 and dark matter (completely) pass through one another, resulting in a displacement of the cluster's mass from its center. This has been observed before in objects like the Bullet Cluster, but El Gordo is much younger and farther away. At 10 billion lightyears distant, the light reaching us now was emitted more than 7 billion years ago, when the universe was less than half its present age. It's a good thing, too, because about 6 billion years ago, the universe began accelerating, meaning that El Gordo just might be the largest cosmic heavyweight of all. There's still more universe left to explore, but for right now, this is the heavyweight champion of the distant universe! Heavyweight (continued) Learn more about “El Gordo” here: http://www.nasa.gov/press/2014/april/nasa-hubbleteamfinds-monster-el-gordo-galaxy-cluster-bigger-than-thought/ Astrophotography—Members Section This month the inbox was treated to a triplet of amazing images by WAC’s own John Gifford. Looking ahead in the 2015 programme for the WAC, John is going to share his astrophotography wisdom 10 July. It is sure to be a great talk. Clockwise from right: NGC2239, the cluster within the Rosette Nebula and therefore the Rosette itself. M45, the Pleiades, “first time that I have managed to catch the nebulosity to some degree.” CR69, cluster at the head of Orion. All were take using the WO 80mm on the EQ6 with a Tele Vue flattener/reducer and a modified Canon 1000D, UHC filter. All 10 x 240sec @ f5.5 and 800 ASA, stacked in DSS, and processed in Photoshop. Imaged from Weymouth. www.weymouthastronomy.co.uk