Is there a formula to give the times when the lunar gravitational effects are strongest and weakest for a location on earth? We considered the tide times, but they factor in variables such as coastal flows and ocean currents, which would adversly alter the calculations

The photos are from our bird bath in the back garden in Bedford this week. There was a hard frost overnight and the water in the bath froze over. This protuding piece of ice was there in the morning. There is nothing overhanging the bird bath in the vicinity and the nearest tree is a long way away. It looks as if something disturbed the water but it surely was not cold enough (around -4 to -6C) for this amount of water to freeze instantly I would have thought. 

I work as a wildlife tour guide in the Scottish Highlands so I travel widely in remote corners of the northern Highlands and islands.

On two occasions in late 2009 I have come across a pile of odd objects (see photos) scattered on the ground. The first time was on a remote island in the Orkneys; the second was a few weeks later at an altitude of around 900 metres in the Cairngorm mountains.

Had they been near a road or habitation I would probably have dismissed them as just some sort of household electronic debris, but in both cases they were miles from anywhere. The pile I found in the Cairngorms was at least a 2-hour walk from any road, track or building.

They appear to have a burnt and pitted charcoal-like solid centre encased in a hard, plastic-like cover. The ones in the Cairngorms also had some small charred battery-like cylinders with them.

Can anybody suggest what they are, and why they ended up in such unexpected locations?

John Poyner, Nethy Bridge, Highland Region, UK

When scientists say no snowflake is the same as another and they are all different how did they find this out? What makes them think out of the trillions and trillions of snowflakes that have fallen two aren't the same and how have they proved this?

Please see: http://imgur.com/zzbEN.jpg

I noticed this frost pattern on a manhole cover in Bern, Switzerland. It was in the middle of the city's Bear Pit enclosure. What could have caused this?

It if it is the 'easy' answer (something star shaped was covering the area), what could it be?

Thanks

p.s. I remember years ago a question similar to this asked on the last word. It was about a spotty melting pattern on paving slabs caused by (it emerged) a technique of adhering the paving slabs using dollops of mortar in each corner of the slab to minimise waste. (Anyone have a link?; I cant find it)

Sometimes, after a heavy rainfall, while watching a puddle to see if there are still raindrops falling in it, I see a tiny bow wave racing across the puddle as if caused by a flea in a speedboat. What causes this?

I look after a pendulum clock at the University of Cambridge which I hope will achieve an accuracy of less than 1 second of error per year (www.trin.cam.ac.uk/clock). It has a temperature-compensated pendulum, but is sensitive to air pressure variation.

If the mean global temperature was to rise by, say, 4 °C, would there be any change to mean air pressure at sea level? Put simply, would global warming cause the clock to speed up or slow down?

Hugh Hunt, Keeper of the Clock, Trinity College, University of Cambridge, UK

I took the attached photos  at Totnes (South West England) rowing club early one morning a couple of weeks ago when the temperature was below freezing.  The icicles originate from the weep holes of the uprights supporting the spiral staircase handrail which is on a very exposed corner of the building. The icicles are formed horizontally and each spiral is about 10mm thick, 400-500mm long and 200 deep. They have been seen before, so it was not a one off. Note that they grow in opposite directions.

This morning I found a huge wedge shaped ice crystal formed on the suface of a garden bucket. It was frozen all around but the water inside the wedge was not frozen. There was nothing in the bucket to stimulate that particular shape to form. It was simply a bucket of water.

I saw the delicate, leaf-like ice crystals in the photo whilst snowboarding in France, they measured from 20 - 80mm and were incredibly fragile. The area they covered in the photo was about 20m2 but we saw other patches close by. The site was at about 1800m.