to latest version of Skywatcher

Equinox Sky Camp—
Trips / Events
Ideas for trips and events
always welcome!
[email protected]
 16 Mar THS - "Einstein's
Universe" Professor Brian
Foster and Violinist Jack
 7 Apr WAS—
Satellites, the history—
Alan Jeffries
 10 Apr CADAS—One
Small Step: A Celebration
of Apollo - Neil Haggath
 5 May WAS—
includes free
evethey? - Len Telford
 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.
The heavyweight champion of the Cosmos! By Dr. Ethan
 2 June WAS—Exhibition
 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,
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:
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
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
All 10 x 240sec @ f5.5 and 800 ASA, stacked in DSS, and
processed in Photoshop.
Imaged from Weymouth.