Wadhurst Astronomical Society Newsletter July 2014
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Wadhurst Astronomical Society Newsletter July 2014 MEETINGS COMMITTEE MEETING Members of the Committee are respectfully reminded that there is a meeting on Tuesday July 1st starting at 0730 in the usual place. JUNE MEETING This meeting was our Open Evening which we always hold on the nearest meeting to the Summer Solstice when the days are longest and the skies are bright for so much of the night. It was open free to all visitors to encourage an interest in astronomy. There were many telescopes present, amongst them was a computerised 6-inch Schmidt- Cassegrain on an alt-azimuth mount brought by John Wayte who also had with him a large pair of 20 x 80 Revelation binoculars on a tripod and his Meade Sky Guide containing a database of over 30,000 objects. John Wayte’s 6-inch Meade Schmidt-Cassegrain and Sky Guide John Vale-Taylor’s incredible telescope for the disabled Phil Berry’s Megrez 80 Refractor on an Astro Track pier John Vale-Taylor brought his innovative “wheel chair” telescope he had made using his experience in engineering and design. This is a telescope through which one can view the night sky from a sitting position and without having to move. It also included an ingenious finder scope. Phil Berry had with him a number of amazing telescopes such as a Megrez 80 appro refractor with a William Optics 20 mm eyepiece and using Robo-focus. This telescope was mounted on an Astro Track pier ideal for the serious astro-photographer on the move. He had also brought a 60ED Zenithstar refractor (ED – Extra low Dispersion) also with a polar-scope mounted for demonstration. In addition he had with him stabilising binoculars and a Coronado PST (Personal Solar Telescope). Following recent storm damage to the church of St Peter and St Paul it was suggested that a ‘Time capsule’ containing an account of life today in Wadhurst should be installed in the church following repairs to be opened in 100 years time. The Society was approached for an inclusion of something about the Wadhurst Astronomical Society. Phil has compiled a piece that includes a photograph of members taken at the meeting and is shown in full at the end of the Newsletter. Our Director of Observation was then introduced to give his talk. Introduction to Astronomy Brian Mills To begin his talk Brian said there are certain questions asked of an amateur astronomer: Is there life on other planets? How far are things away? And they nearly always ask how much did your telescope cost? We are all familiar with distances on Earth with but Brian began to look further afield with how we measure distances in space. The distance from the Earth to the Sun is 149,598,261 km which is in a metric unit of measurement we are all familiar with but this is cumbersome when we talk about the Solar System where we more usually use the Astronomical Unit, the AU; the distance from the Earth to the Sun. On this scale the distance to the Moon is 0.0025 AU, Saturn is 10 AU from the Sun, Uranus 20 AU and Neptune 30 AU. This is ok for the Solar System but greater than this we use the speed of light, 300,000 km per second as our measuring stick. The nearest star after the Sun is Proxima Centauri; the light from this star takes just over 4 years to reach us so we say it is 4 Light Years away and the next, Barnard’s star is at a distance of 6 light years. Another unit Brian referred to was the Parsec although this is usually only used in scientific papers. If the position of a star is recorded from Earth and then its position is measured 6 months later in its orbit the nearer stars would appear to have moved relative to the background stars. If this angle divided by 2 has changed by 1 arc second; 1/60th of one arc minute or 1/3600th of one degree then we say the star is 1 parsec away which is also 3.3 light years. Now Brian turned to the question of what the Earth is made of although as he said quite a lot of the interior of the Earth is of a plastic nature rather than solid. The interior structure of the Earth The average diameter of the Earth is 12,734 km but because of centrifugal force the polar diameter is 12,712 km and the equatorial diameter is a little more at 12,756 km. We looked next at the Earth’s atmosphere. The lowest 20 km is called the Troposphere and contains 80% of our atmosphere and the temperature towards the higher part reaching as low as -60° C. At the top of the Troposphere, we come to the Stratosphere which continues up to 50 km with a temperature rising to about freezing due to Ultra Violet absorption. The Mesosphere is next, reaching to 85 km above the Earth’s surface and is where meteors burn up and any water vapour forms Noctilucent clouds. The temperature here can be as low as -100° C. The next layer, up to 690 km, is the Thermosphere with temperatures reaching 1,500° C. The lower part is where Auroras occur and further up is the orbit of the International Space Station at about 400 km. The fact that there is still a slight atmosphere here means that every now and then the station requires a boost to overcome atmospheric drag. Finally, up to 10,000 km is the Exosphere containing mostly hydrogen and Helium and we were told that the particles here are so far apart, they almost never collide. Brian looked at how the Moon was formed. He said the most popular theory at present is that in the distant past the Earth was struck by a Mars sized body subsequently given the name Theia. The resulting strike may be why the Earth’s axis is at an angle to the plane of the Sun but this does give us the seasons. The phases of the Moon we see were explained and we were told that the best time to see the Moon’s craters is not when light from the Sun is full on but is at an oblique angle, revealing the walls of the craters by their shadows. One face of the Moon is always directed towards us but due to the Moon’s elliptical orbit around the Earth, there are times when it travels faster or slower and this enables us to see a little bit more round the side. Also, because the plane of the Moon’s orbit is not the same as the Earth’s, at times we are able to see a bit more of the Moon’s north or south polar regions. This oscillation of the Moon as we see it from Earth is called Libration. Brian presented a short explanation of a lunar eclipse and gave the reason why the Moon sometimes appears deep reddish in colour due to light from the Sun passing first through the Earth’s atmosphere. He also explained the difference between a total Solar eclipse, when the Moon is closer to us and an Annular eclipse when the Moon’s orbit takes it further away and is visually smaller leaving a bright annular ring. This was followed by a quick explanation of the effect of the Moon’s gravity on the fluid oceans and to a lesser extent by the Sun’s, causing the tides. We were introduced to the interior of the Sun where the core is 15M° C; hot enough to fuse hydrogen and helium at the rate of about 500 million tons a second. Surrounding this is the Radiative Zone and further out, the Convection Zone a 2M° C. Then there is the Photosphere at 6,000° C which is what we see. Surrounding this is the Chromosphere at 20,000° C which we see during a total eclipse, and finally the Corona at 2 to 3M° C. Brian very sensibly warned against looking directly at the Sun without any eye protection. The human eye can be permanently damaged by direct sunlight in an instant. and advised using a Mylar filter or projection methods Brian completed his description of the Sun by talking about sunspots which he said occur in a pattern over an 11-year cycle. Early in the cycle, sunspots form in the higher latitudes but as the cycle progresses, they appear closer to the equator. He showed a graph of sunspot latitude against time, known as the Butterfly Diagram because of its appearance. The Butterfly diagram - NASA The graph shows the difference in activity over many years. We looked at different stars compared with our Sun. Two particular stars in the constellation of Orion are good examples. Rigel is the brightest in the constellation but compared in size, red Betelgeuse is by far the largest. We were told that Betelgeuse is predicted to become a super-nova soon and at 640 light years away, may already have done so, although the light hasn’t reached us yet. On the same size scale by comparison, the Sun is so small it is almost lost. Brian then looked at the bigger picture starting with the Milky Way of which the Solar System is only one tiny component. Our galaxy contains between 100 and 400 billion stars, is about 1,000 light years thick and something like 100,000 light years in diameter.