23 May 2013 – Over the next few days, the solar system’s two brightest planets will be drawing closer together in the evening sky. Venus and Jupiter should be about 5 degrees apart tonight, moving towards a grand conjunction on Tuesday 28 May when they’ll only be 1 degree apart in the sky (though of course still separated by millions of kilometres of space).

In the meantime the fainter planet Mercury will have a conjunction with Venus on 25 May, and then with Jupiter on 27 May. The three planets will appear as a triangle in the twilight sky, and all three should fit within a single binocular field from about 24-29 May (closest together on 26 May). This is the closest grouping of the three planets until 2021. Strictly speaking it’s not a triple conjunction (though there will be three separate planetary conjunctions), but a ‘planetary trio’.

Look out for the three planets in the western sky from sunset each evening. Let’s hope for some clear skies!

If you’re an avid museumgoer like myself – or if you’ve got kids who are – you may have noticed the multitude of interactive exhibits now gracing the halls and galleries of museums across the UK; or maybe I just deal in highly esoteric material. While the ROG currently has a number of successful interactive galleries in the Astronomy Centre, its previous interactive exhibits didn’t always fair as well or attract as much fanfare. The ‘Sadlerium’ – one of the ROG’s first attempts at producing an interactive exhibit, – is a brilliant case in point, and is perhaps better viewed a lesson in how not to design and build an interactive exhibit.

Named for its designer and champion Donald H. Sadler, Superintendent of the Nautical Almanac Office from 1936-1970, the Sadlerium was an attempt to teach the taking of lunar distances for the Observatory’s 1967 exhibition ‘Man is Not Lost: A Celebration of The Bicentenary of the Nautical Almanac’.

In the years before Harrison’s marine timekeeper, an observer on the deck of a ship in the middle of the ocean could identify his or her longitude by using the moon as a sort of ‘watch hand’ and measuring the distance between the moon and any easily identifiable celestial bodies that lay in its path as it traversed its way across the heavens. We won’t get into the method of lunar distances in too much detail here, but if you are interested, Wikipedia has a fairly good summary.

In his initial designs Sadler promised that his Sadlerium would “illustrate not only the method of lunar distances but also latitude sailing and modern methods of position finding” and would be intelligible to average “secondary schoolchildren”.

It would be an ambitious exhibit, consisting of a rotatable globe connected by a system of wires and pulleys to a moon that would journey across a canvas sky chart as the globe rotated.

Museum visitors were encouraged to picture themselves on the deck of a ship heading west across the Atlantic. As the ship sailed from the western shores of England to somewhere in the middle of the Atlantic – denoted by a moving sea chart on the floor between the visitor and the sky chart – visitors could measure the distance between the moon and three carefully chosen and brightly illuminated ‘identifier stars’ by peering through a nearby sextant. They could then compare these measurements with the nautical almanac on the table beside them and identify their position.

At least, that was the intention. What resulted, was a complex mess of wires, pulleys, sextants, and charts that spent more time in disrepair during its first six months than it did in working order. In March 1967, due to “some trifling mechanical trouble” the complex pulley mechanisms seized up, and the Sadlerium sat non-functional for the next four months. The public then proceeded to detach the sextants from their mounts and cranked the wheel so hard that the entire chart became detached from its frame and sagged towards the floor. Not the most auspicious start…

As if that weren’t bad enough, curators from the ROG began to question whether the Sadlerium – even a fully functioning Sadlerium – would be able to teach visitors anything about the taking of lunar distances or marine navigation. Though intended for secondary schoolchildren, W.E. May, an author on maritime history and curator at the ROG, felt that the Sadlerium used far too much industry specific jargon and doubted whether anyone would be able to take anything of value from the exhibit. The original instruction placard can be seen below:

If that made little sense or if you stopped reading halfway through to nurse a headache, don’t worry, you are not alone; your 1960s brethren wholeheartedly agreed. As May criticized:

The proposal is to put instructions for the use of the instrument alongside it but I cannot conceive how anybody will ever be able to gain much from this, particularly if the standard of description is anything like that used in an attempt to describe lunar distances on the blackboard next door (seen on the side wall in Image #5 above).

May then chimed the death knell for this first incarnation of the Sadlerium when he concluded it had been “ill-conceived, ill-planned, and badly executed”, and noted that even if the exhibit were repaired (at some expense):

… unless someone with more knowledge [...] is permanently stationed alongside the instrument to demonstrate it there is every likelihood that it will almost constantly be out of order and visitors will obtain little information from it.

This was, in some small way, vindication for engineers from Oriel Équipe Ltd, a small design firm that specialized in designing and constructing museum exhibits whose bid for the Sadlerium had been rejected by ROG officials for being too pricey. Oriel had recently designed and installed the highly successful Interactive Periodic Table at the Science Museum two years prior (seen below), so they knew a thing or two about how to create a successful interactive exhibit.

In a moment of near clairvoyance, Oriel actually predicted the fate of the Sadlerium during the final paragraph of their unsuccessful bid:

… having examined the project as designers who specialize in museum work of this kind, we have come to the conclusion that as conceived at present the exhibit will be extremely expensive to make and difficult to operate efficiently. We are not fully confident a good teaching exhibit will result.

“Such an exhibit made to suitable museum standard and easy to maintain”, wrote Robert Wetmore, head designer at Oriel, “would certainly run well into four figures”. The ROG, confident that it could construct the Sadlerium itself using engineers from the Royal Observatory Herstmonceux, was loath to spend more than £200.

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Despite these myriad difficulties, however, it seems a second, sturdier version of the Sadlerium survived until at least 1969 when it was dismantled and reassembled in the old Caird Planetarium building underneath the Thompson dome. Thus ending the long, strange saga of the Sadlerium – an exhibit designed to teach the taking of lunar distances that seemingly taught curators more about how (and how not) to build a practicable interactive exhibit than it taught visitors about lunar navigation.

On Thursday evening there will be a penumbral and also partial lunar eclipse visible from the UK.

A penumbral lunar eclipse occurs when the Moon travels only through the outer, fainter part of the Earth’s shadow, or ‘penumbra’. This happens when the Earth moves between the Sun and Moon but the three do not form a perfectly straight line. The penumbra causes only a slight darkening of the Moon’s surface, with the Moon still exposed to some direct sunlight, so this type of eclipse is easy to miss.

During the partial phase of the eclipse, part of the Moon travels through the Earth’s full ‘umbral’ shadow. However, on this occasion only a very small section of the Moon will be covered by the umbra at maximum eclipse, though the whole northern half of the Moon will be darkened by the penumbral shadow.

The penumbral phase of the eclipse should start at about 19.03 BST, though it will only be visible after about 20.00 in the UK as before that the Moon will be below the horizon. Roughly speaking, moonrise is earliest toward the east of the UK, latest toward the West (about 20.11 in London and 20.44 in Glasgow on 25 April).

The partial phase of the eclipse begins at 20.54 BST, with greatest eclipse at about 21.07 when the Moon is closest to the centre of the Earth’s full shadow. The Moon will still be near to the horizon, so you’ll need a clear view to the East to see it. The partial eclipse ends at 21.21 after only 27 minutes, making it the second shortest partial lunar eclipse of the century. The penumbral phase ends at 23.11, bringing the whole event to a close.

There will be three lunar eclipses in 2013. However, only two are visible from the UK, the other taking place on 18-19 Oct 2013. Sadly we’ll have to wait till March 2015 for the next Solar eclipse that can be seen from these shores.

19 April 2013 – The annual Lyrid meteor shower is underway and should peak before dawn on Monday 22 April. This year the nearly-full moon is likely to impede viewing, so after midnight from a dark location should give the best chance of seeing shooting stars.

The Lyrids are a reliable annual shower of bright fast meteors associated with Comet Thatcher. The shower gets its name from the constellation Lyra, from which the meteor trails appear to radiate. The shower usually lasts from about 16–26 April.

The Lyrids typically produce between 5-20 meteors per hour at peak, but occasionally the Earth passes through a thicker part of the comet’s dust stream resulting in a more intense shower. In 1982 amateur astronomers counted 90 Lyrid meteors per hour, and in 1803 an even stronger ‘storm’ was observed of up to 700 per hour.

Most Lyrid meteors are around magnitude +2 (roughly similar brightness to the stars in the Plough). A few though, known as ‘Lyrid fireballs’, can be much brighter, casting shadows for an instant and leaving smoky trails of debris.

The Lyrids were first observed 2700 years ago by Chinese astronomers, making them the earliest-known meteor shower.

The next notable annual meteor shower is the Eta Aquarids, a light shower associated with Halley’s Comet and due to peak around 6 May.