Astronomy and the Speed of Light - Prof Bob Lambourne – 21st November 2018


To measure distance these days you need, not a ruler, but a clock! For the metre is the length of the path travelled by light in vacuum during a time interval of 1/299792458th of a second.

The metric system was originally conceived as a system of measurement derivable from unchanging phenomena; but technical limitations necessitated the use of artefacts (the prototype metre and prototype kilogram for example) when the metric system was first introduced in France in 1799.

But in the same way that has been done for the metre, from 20th May 2019 the kilogram, ampere, kelvin, and mole will be defined by setting exact numerical values for the Planck constant (h), the elementary electric charge (e), the Boltzmann constant (k), and the Avogadro constant (NA), respectively.

The November lecture from our Vice President Prof Bob Lambourne, focussed on the history of the determination of the speed of light, such that now it is deemed to be a fixed value – a constant in the same way as the Planck or Boltmann constants.

Galileo in 1638 started it, coming up with a value of about 200,000 km/s, but admitting it was actually too fast to measure. Then through the work of Bradley, Huygens and Newton in the 18th Century; Fresnel, Fizeau, Foucault, Michelson and Morley in the 19th Century to arrive at estimates closer to 300,000 km/s; culminating in the theories of Lorentz and Einstein in the 20th Century. Along the way, the notion of the “ether” was invented and discarded, and Einstein’s Theory of Relativity showed how to relate measurements made by observers in a specified state of relative motion. Whilst “c” does represent the speed of light, its real significance is that it is the fundamental constant in all space-time physics.

Not strictly a lecture about astronomy, this was a welcome revision of this corner of the history of science. The Society wishes Bob a happy retirement from his post at the Open University and we are extremely pleased that he will continue to be our Vice President and wants to come back and give us more lectures!

Sandy Giles

Sandy Giles at Wycombe Sound Radio – 13th November 2018


Continuing his monthly series of chats with Mick Lewis of Wycombe Sound Radio, WAS’s Sandy Giles this month was talking about the use of his new ZWO video camera for taking lunar images. He also fielded a question from a listener recently back from a trip to South America, why could she see more stars in the southern hemisphere that she sees at home – likely because there was less light pollution and atmospheric disturbance. Sandy also discussed the end of one space mission (the Kepler Space Telescope) and the beginning of another (the BepiColombo mission to Mercury).

You can listen to show here: and click on, Afternoons_Tuesday 13 November 2018.

Sandy’s next interview will be at 2:00 pm on Tuesday 11th December (106.6 FM).

Photographing the Deep Sky – A Journey through Space and Time Chris Baker – 17th October 2018


Having visited us a couple of years ago, Chris Baker did not dwell overlong on the description of his telescope five thousand feet up in the mountains of Spain. He is an early pioneer of remote astro-imaging, having available over 2000 hours of imaging time available each year and being able to control, from wherever he is, his 6 inch Takahashi Refractor equipped with a QSI683 CCD camera fitted with eight filters (L, R, G, B, Ha, Hb, SII and OIII).

He primarily wanted to show us his images taken over the last few years with this equipment and chose to present them in order of their distance from Earth, illustrating at the same time what was happening on Earth at the time the light left a particular object.

Having briefly got past the Solar System (he’s not ashamed to admit he’s not a planetry imager!) the first port of call was the Pleiades, the light from which left 440 years ago, when Elizabeth I was our monarch. Demonstrating clearly that faint nebulosity surrounding this cluster (achieved by incorporating a Ha image into the blue channel) we knew from the outset what a treat we could expect for the rest of the evening. Then followed magnificent images of the Dumbbell Nebula (1,350 ly), part of the Veil Nebula known as Pickering’s Triangle (1,470 ly) the Horsehead and Flame Nebulae (1,500 ly) and the Pelican Nebula (1,800 ly).

Onwards and outwards we went – the Elephant’s Trunk (2,600 ly), the Cocoon, Crescent and Rosette Nebulae (all about 3,000 ly) and the Bubble Nebula (7,500 ly). Finally, whilst still in the Milky Way, out to stars as old as the galaxy itself, the globular clusters M13 (22,000 ly), M5 (24,460 ly) and M3 (33,900 ly). All fabulous images in gloriously deep colours, with amazing clarity and depth. Some of these images involved over 50 hours of exposure!

After this of course, a big gap – because we needed to step out to neighbouring galaxies. M31 (2.5 mly), M33 (2.7 mly), M51 (23 mly), the Virgo Cluster (65 mly). Finally Chris showed us an image he took of the furthest object in his collection, Abell 2065, a galaxy cluster one billion light years away!

With great images, an engaging presentational style and a book of his images available for purchase afterwards for those that wanted, we had a most enjoyable evening. And for all of us aspiring astro-imagers, a clear message – must try harder!

Sandy Giles

Aurora - Dr Melanie Windridge – Wednesday 18th July 2018

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Melanie Windridge has explored the science and mythology of the Northern Lights and this month she shared many of the stories of her quest to explore her fascination in and our understanding of the Earth’s Aurora. Melanie is a physicist, specializing in fusion research. She is also an adventurous traveler, particularly at home in the world’s coldest places.

She shared the experience of her visits to many places where the aurora is visible – Lapland, Iceland, Canada, northern Scotland, and Spitzbergen – and of meeting people for whom the Northern Lights plays a significant part of their lives. She travelled, for example, with Sami herdsmen in northern Norway and learned of Sami mythology and the gradual dwindling of their nomadic way of life.

Dr Windridge interweaved these stories with explanations of the science of the Northern Lights. Aurora occur when electrons and protons, which are charged particles and form the greater part of the solar wind, interact with Earth’s magnetic field and elements in the earth's atmosphere. Solar winds stream away from the sun at speeds of between 300 and 750 kilometers per second. They reach the Earth some 30 to 40 hours after leaving the sun. As the electrons enter the earth's upper atmosphere, they will encounter atoms of oxygen and nitrogen at altitudes from 20 to 200 miles above the earth's surface. The colours generated relate to the energy levels available in atoms that are struck. Nitrogen producesthe blue and purple and oxygen produces green and red.

The auroras generally occur in ovals which centre on the magnetic poles and roughly correspond with the Arctic and Antarctic circles. There are times, though, when the lights are farther south, usually when sunspot activity is high. Sunspot activity follows an 11-year cycle. The next peak will occur in 2022.

Melanie highlighted the dangers that space weather poses for satellites in orbit, and for the power grid on the Earth’s surface. She outlined her own efforts to view the aurora, illustrating with her best attempts to capture an image how difficult it is to photograph the aurora’s rapidly-changing structure.


Humans in Space – What’s Next? Libby Jackson – UK Space Agency

Humans first went into space in 1961, landed on the moon in 1969, and have been continuously living and working on board the International Space Station (ISS) since 2000. But where will we explore next?  This was the question UK Space Agency’s Libby Jackson posed at our lecture meeting this month.

The Moon landings were all about exploration (arguably, actually, they were all about politics!) – and in contrast the activities aboard the ISS are all about science, part of which is to understand the effects of prolonged exposure to space travel on humans. The next phase in space flight is reverting to exploration with visions of trips to the Moon and Mars. But we have enormous problems to overcome.

Propulsion for example. For the Moon missions the Saturn rocket could lift a payload of 40 tons for a two week trip. The ISS is the size of a 5 storey building and took many missions to build it to its present size and functionality, and is constantly being re-stocked. A journey to Mars will take 9 months, then 6 months there waiting for an appropriate planetary alignment before setting off back, and another 9 months to return to Earth. The resources needed for such a trip will require an approach to getting stuff into space some orders of magnitude greater than what we currently have. The advances made by the likes of Elon Musk and his Space X operation may be the way forward here.

Astronauts will need to be protected from solar radiation because unlike us on Earth, protected by the Earth’s magnetic field, they will not have such shielding either during their journey or whilst on Mars itself – Mars has lost its magnetic field, remember. Right now, no technology exists to provide such protection (putting them in a lead spacecraft, for example, is impractical due to the weight).

The physical well-being of astronauts in long terms space flights is beginning to be understood – in short, space travel causes instant ageing (for example Calcium very quickly leaches out of bones under zero gravity resulting in osteoporosis). Solutions to this and to have astronauts who can actually function on arrival at Mars, will need to be devised.

Landing will pose problems too – it’s a sobering thought that half of all Mars missions so far have failed in this regard. Mars has very little in the way of an atmosphere and the problem of opening a parachute in a near vacuum (if this were to be the mechanism chosen) has yet to be solved.

Communications at these distances is lengthy. At maximum Earth-Mars separation for instance it would take a radio message 24 minutes to travel one way. Astronauts on the ISS or even the Moon are accustomed to more or less instant communications. The Apollo 13 mission recovery required constant and immediate dialogue between the stricken spacecraft and Mission Control. A different level of autonomy and self-sufficiency will be needed by the astronauts.

And how would astronauts cope psychologically over a 2 year period eating dried rations and being out of direct communication with friends, family and Mission Control? Simulations of such conditions on Earth have been carried out so at least a partial understanding is being gained here.

Finally, there are ethical, legal and environmental questions which require solutions – bio-protection is an issue even here on Earth when we start exploring the Arctic for instance. Indeed should we even consider going to Mars, risking us contaminating the Red Planet, or even bringing Martian contaminants back to Earth?

It has taken almost 60 years to get to where we are in space exploration from when Yuri Gagarin became the first person to orbit the Earth. Libby Jackson highlighted the formidable gaps in our knowledge and technology to take the next steps in space exploration. Nevertheless she remained upbeat about overcoming them and was optimistic that in her lifetime she would witness humans on Mars.