By Mike Frost
Here's an account of my (succcessful, just) viewing of the Transit of Venus with my friends from Rugby & District AS, and a trip with the SHA to Much Hoole.
Eight years ago, June 8th 2004 was one of the great days of my life. At 6:19 that morning, in my back garden, I watched Venus slide onto the disk of the Sun, a sight not seen for a hundred and twenty two years. Later that day I drove to Cambridge to view the transit of Venus from the Institute of Astronomy, and then speak at an event in celebration of the first man to predict and then observe a transit, the young Scouse astronomer Jeremiah Horrocks.
By June 2012, Earth had orbited the Sun a further eight times. By a curious co-incidence, Venus had gone round the Sun almost exactly thirteen times, and so Sun, Venus and Earth returned to almost the same configuration, giving a second transit on June 5th / 6th 2012. However, as well as being two days earlier, the domain of visibility of the Transit was very different. In 2004 we had a view of the entire spectacle from Britain; this time round the Far East, Australia and the Pacific were blessed with an unbroken view, and the UK had to make do with just the last hour or so, at dawn on Wednesday June 6th.
I had the opportunity of joining a trip to America to see the Annular eclipse of May 20th from Arizona, and then the transit of Venus from Hawaii on June 5th, but decided instead for my astronomical holiday to travel to Australia later in the year to see the November total eclipse. For sentimental reasons, I decided to stay in England for the June 6th transit. If 40 minutes of transit, ending at sunset, was good enough for Jeremiah Horrocks, then 80 minutes of transit, starting at dawn, was going to be good enough for me.
Because the Sun was going to be low in the sky throughout the transit, as viewed from England, I made some enquiries as to where a clear north-east horizon might be seen. Suggestions included Kings Newnham and Burton Dassett. Rugby Astronomical Society were going to organise a star party at Napton-on-the-Hill, but when that went through they opted instead for Anita’s Caravan Park, Mollington, in the hills on the Southam road heading north out of Banbury.
In 2004, the main story in the days leading up to the Transit featured a sixtieth anniversary, of the D-Day landings. For 2012 we had a different sixtieth anniversary, the Queen’s diamond jubilee, of course. You won’t need me to remind you that the celebrations of that event were dampened by some downpour; especially the flotilla on the River Thames. So the weather prospects for transit day did not look good.
I drove south to Mollington on Tuesday evening, arriving at 7:30 in pouring rain. Not owning a tent, I was planning to sleep in my car, but this was unappealing on a wet, cold evening. I knew that there a few “pods”, essentially wooden tents, for hire, and was delighted to hear that one was free. On the way to my pod I bumped into Rob Sime from the Rugby AS, who told me that the others in the party had already left for Pizza Hut in Banbury. For my meal I drove to the Castle at Edge Hill, an extraordinary pub overlooking the Civil War battlefield, and enjoyed chicken pie, chips, and a pint of Hook Norton. By 9:30 that evening I was in my pod, warmed toastily by the heater, and turning in for an early night.
I was woken at 3:45 AM by light streaming in through the pod window. For a moment I thought it was a bright pre-dawn, but when I poked my head out the door I realised that the sky was still completely overcast. At least it wasn’t raining!
I retrieved my telescope, binoculars and eclipse shades from my car, and, lacking a white card to project the Sun’s image onto, commandeered the campsite’s pub guide as an emergency projection sheet. I shuffled across the campsite to the Rugby AS corner. People were beginning to stir.
Dawn was at 4:30 AM. As my fellow astronomers emerged from their tents, we discussed what the best observing options were. The campsite was essentially farm fields, bordered by hedges, and so we did not immediately have a clear horizon to see the Sun as it rose. On the other hand, there was no possibility of seeing sunrise as the clouds were ubiquitous to the north-east. More encouragingly, in the opposite direction we could see one or two breaks in the cloud, which we could see were headed in our direction. When the Moon, near-full, appeared in one of the breaks, we were heartened.
Rob decided to stay in the campsite with a large telescope, but the rest of us opted for the clearest horizon we could find. Seven of us; Jo and Alex Jarvis, Roger Jackson, John and June Walker, Sarah Meek, and myself, walked to the north corner of the campsite, over a stile onto a side road, and then across the A423 into a field, which sloped gently downhill towards the north-east.
We set up two small birding scopes, and tried them out by focusing on the Arbury Hill radio mast, ten miles away. Three more people turned up; David Morris, and unexpectedly, Georgie and Anton, a couple from Banbury who had got wind of our little party. Five o’clock came and went. The sky was certainly clearer, with occasional patches of blue to the south and west, and even a glow in the clouds to the east which indicated the approximate position of the Sun.
Five thirty – not long left now. The Banbury couple had left for home. A particularly evil looking cloud loomed overhead, but fortunately it was low and passed quickly. We discussed why we hadn’t chartered a private plane to take us above the cloud. And then we noticed that a patch of sky was headed towards the glow of the Sun.
Could it be? Could it be? The glow brightened, brightened … and then the Sun burst through! Almost taken by surprise, we turned the scopes to catch the rays. My emergency white sheet was pressed into service. Were we in time? 5:43 PM, and the projected disk of the Sun had a tiny nibble at about 4 o’clock on the edge. We were way past third contact – but there was Venus, still clinging to the solar disk by its fingertips.
Whooohooohohoo! “A most agreeable spectacle” I intoned, quoting Jeremiah Horrocks, and was teased for regurgitating a much-rehearsed line. High fives all round, and photographs of the projected disk to prove we’d struck lucky. And an explanation for the youngest member of our party – Alex Jarvis, at three years of age, the only one of us who stands any chance of seeing this event again. When the next transit comes, in December 2117, Alex will be 108 years old. The rest of us will be dead.
Five minutes later, the hole in the clouds closed, and that was the last we saw of the transit.
But we saw it.
Left; Captain Cook display.
Right: Allan Chapman in full flow. Note the hymn numbers - 20 12, 16 39
Left: The window of Carr House from which Horrocks may/may not have observed
Right: The stained glass window at Carr House
We weren’t the only people to strike lucky in the Midlands. A small group from Stratford AS was at Burton Dassett Country Park, four miles to the north-west of Mollington. John Waller reported that the extra altitude gave them a view of Venus whilst it was still completely on the solar disk. Viv Porteous, meanwhile, reported an excellent view from Coventry airport, and one of Viv’s pictures featured on the BBC’s breakfast news. Well done! The weather front that had given us a few sporadic gaps in the cloud seemed to cross the country from the north-west, through the west midlands, west of London down to Sussex, and observers along this track reported success on the Stargazers Lounge website. Elsewhere in Britain observations were negative.
On Saturday, June 9th, the second part of my transit celebrations took place at the village of Much Hoole, on the Liverpool road out of Preston. This was the village where Jeremiah Horrocks was living when he made his predictions of a transit in November 1639. We don’t know for certain what he was doing in the village (he never tells us in his surviving papers) but as an educated young man a role as tutor to the local landowners, the Stones family, is plausible. A role in the local church, St Michael’s, is also highly likely. The Revd. Robert Brickell, rector of St Michael’s during the transit of 1874, insisted that Horrocks had been a predecessor as curate of St Michael’s, but there is no evidence for this, and indeed he would have been too young; a more likely post for him would have been bible clerk, reading the lessons.
At St Michael’s they are very proud of Jeremiah Horrocks. A stained glass window of him observing the 1639 transit stands behind the altar, and two more stained glass windows commemorate the transits of 1874 and 2004. An imposing Victorian plaque honours the life of “Revd. Horrocks”. When I visited the church in 2004 the village had put on an extraordinarily beautiful and moving flower festival to commemorate the transit (echoing perhaps Robert Stawell Bull’s evocative quote about the transit of 1882, “this pleasing picture, a repetition of which will not occur again until the flowers are blooming in June 2004 AD”). This time round the church display was a little more restrained, but there were still a number of new exhibits to commemorate Captain Cook and other transit observers. On the Tuesday evening, after a celebratory evening, the parishioners had set up a big screen to display NASA’s live feed of the transit from Hawaii, sidestepping neatly the vagaries of British weather. Plans were also afoot to commemorate the 2012 transit with a new, transit-themed weather vane on the church tower.
The Society for the History of Astronomy, in the person of Kevin Kilburn of Manchester AS, had organised the Saturday event, and fifty of us had come along to the church. I brought my mum, who I had taken to St Michael’s once before, in 2008, when we attended the Sunday morning service, and were made very welcome
You won’t be surprised to learn who preached to us from the pulpit – Dr. Allan Chapman, of course, who has made a study of his fellow Lancastrian astronomers Horrocks and William Crabtree. Allan started by telling us that he too had been a successful observer of the transit, from Oxford, encountering a gap in the clouds in similar circumstances to the Rugby AS party twenty-five miles to the north. He then went on to deliver a typically exuberant lecture on Horrocks’s life and times.
Was Jeremiah Horrocks from a rich family? No – the benefit of a university education at Oxford or Cambridge was not usually taken by the wealthy, who had their own tutors; rather by the bright sons of yeomen farmers and tradesmen, who were able to send their sons to receive an education which could turn them into professionals, usually clergymen or lawyers. Was this education prohibitively expensive? No, not excessively so, because the university colleges had benefactors, wealthy men who founded seats of learning, to supply them with a stream of students who would pray for their souls and so provide them with an exit from purgatory into heaven. Were Horrocks’s own beliefs, forged in the Puritan stronghold of Emmanuel College, Cambridge, at odds with the more mainstream beliefs of St Michael’s? Not necessarily; Dr. Chapman argued that the differences between different Christian sects were often bridged by personal friendships and professional relations. Horrocks might not have agreed with the finery and ceremony of worship at St Michael’s (for example, silver communion cups, dating from the 1620s, which were on display on the altar) but he could live with it.
It was, in short, vintage Chapman, including swipes at two of his favourite targets; modern, theory-oriented historiography, and his disdain for what he regards as the unwarranted gap between modern-day science and religion. Allan preferred historians to chart the real, everyday stories of the connections between people; and scientists to be comfortable with religious faith in the same way that Horrocks and his contemporaries were. Opinionated, of course, but very entertaining.
But there was another treat waiting. After Allan had finished, half the audience left the church and made their way to Carr House, about 1 km to the south. This was the home of the Stones family, who built St Michael’s, and the building from where, local tradition has it, Horrocks made his observations. (The other half of the audience had already made the trip)
I had seen Carr House from the outside several times previously, but this time, by kind permission of the owners, Clive and Jane Elphick, we were able to go through the door, and see the house from the inside.
Carr House had fallen into disrepair until the 1950s, when it was renovated. It was a museum for some years, and then became a private house. Clive and Jane acquired the house in the early 2000s, and realising its historic significance, went about creating a fitting memorial to Jeremiah Horrocks, as well as a comfortable private house. For example, there was a secular copy of the stained glass window commemorating the 2004 transit in the stairwell, and excerpts from Horrocks’s notebooks, framed on the walls.
But what I most wanted to see was the window bay in the master bedroom, on the first floor – the window through which Jeremiah is reputed to have made his observations. There’s some evidence that the room, now spacious, was subdivided in Horrocks’s day, so the window might have been part of his lodging. There is an antique telescope on display, to suggest the “half-a-crown” scope with which Horrocks projected the Sun onto gradated paper, and noted the position of Venus at three times, 3:15, 3:30 and 3:40, before the Sun set at around 3:45.
It isn’t certain that this was the window, because the view of sunset on Sunday 24th November 1639 [date old style] would have been barely visible, and certainly very difficult to project, from the angle at which the window looks out. Would Horrocks have risked all by setting up equipment in a location that might have missed seeing the last minutes of the transit? In a recent paper in Astronomy and Geophysics, the RAS house journal, Kevin Kilburn and Clive Elphick argue that the line of sight makes it unlikely that this window was the location of Horrocks’s observations. There are west-facing windows in the building with a better line of sight, but none of them are thought to have been openable in 1639.
So, there is some doubt that Carr House really was the location of Horrocks’s momentous observations – but if not there, where? However, for the duration of our visit to Carr House, I suspended my doubts. As far as I was concerned, I was standing in the footsteps of Jeremiah Horrocks as he watched the sky on that cloudy, oh-so-Lancastrian, November afternoon 372 years ago, and then reported:
“The clouds, as if by divine intervention, parted, and I beheld a most agreeable spectacle, the object of my sanguine wishes, a spot of unusual magnitude and of a perfectly circular shape … the planet Venus”
The Last Transit
By Ivor Clarke
Just before the alarm went off I woke up! How many times does that happen? An alarm clock is already built into your brain it seems. It was 4.20am, not dark, with a grey light coming past the curtains. I got up and looked outside, cloudy in the east through the bedroom window. Drat! Looking west through the second bedroom window was cold blue sky. That looked more promising. I decided to risk it and try to see the sun rise with Venus on its face, the last transit of Venus in the 21st century. If I didn't try I may always regret it and what would I lose, just a couple of hours sleep in a nice warm bed, hmmm.
I got up, dressed warmly, picked up the camera bag and a Gorillapod mount to hold the camera on a fence, filters and kit and walked the short 12 minute walk into our local park at Bedworth. I had done this walk a few days earlier to time it, and walked into the far south eastern corner of the park next to the Nuneaton — Coventry local train line. From there a small rise by the fence gave a view of the north eastern horizon. I had checked with a compass to make sure I had the right direction, where the sun would rise at about 4.50am, over the rooftops of the local houses. From there I had a near perfect view of the horizon. But of cause it was cloudy in that direction!
Over head the sky was clear and blue but a large double bank of clouds hid the sunrise. The wind was coming from the right direction to blow them away, but was it strong enough? Would it take longer then 50 minutes? If it did I might as well go back to bed.
Watching the sky proved my worries right, there were two layers of cloud across the eastern horizon. And one of them didn't seem to be going in the right direction. It was getting much brighter now with the clouds having a silver rim. Behind me the 15 day old moon hung in clear sky, but with another bank of clouds approaching swiftly from the west. Will the eastern clouds move in time? Will Venus still be visible?
By now it was 5.30am, so I took a shot of the moon between streaky layers of cloud to prove that there was clear sky about. One or two of the park's early morning dog walkers and joggers went past on the path, but no one came to ask what I was doing standing by the fence in the long wet grass. I knew where the sun would rise at dawn but now it would be getting higher and hopefully clearing the misty, streaky clouds. The last time I saw the transit was in June 2004 from Cyprus by the hotel swimming pool (see MIRA 66), then it was hot and sunny, now it was cold and dewy and damp and early.
With me I had a couple of solar filters, but looking through them was a waste of time as they were much to dark to see anything of the rising sun trying to penetrate the wispy tops of the clouds. I also had some old sheets of 5x4 black and white film developed to a good density. These are safe if dark enough and I found one not too dark which showed the top of the sun above the clouds and there, through a small 8 x 20 monocular, I think I saw Venus right on the edge at about 5.40am, but it was very hazy through misty cloud and looking through the sheet film didn't help much. I took a couple of shots but they didn't show much more than a misty patch.
So not a complete failure, but if only it had happened a day earlier, then clear skies covered nearly the whole country. The joys of astronomy from the UK.
A Canadian Transit
By Mark Edwards
After our successful viewing of the transit of Venus in 2004, where the society set up telescopes outside the cathedral in Coventry, I had not taken much attention to the occurrence of the next one. It was only last year as 2012 drew ever closer that I forced myself away from the hype of the forthcoming Olympics to concentrate on that other major event of the year, the next transit of Venus.
Transits occur in pairs separated by 8 years, as 13 orbits of Venus are nearly equal in length to 8 orbits of the Earth. So if a transit occurs one year, Venus and the Earth will be close to the same position 8 years later.
The 2004 transit took place on June 8th, so the next transit would be just two days earlier in 2012. Some reports claimed that it would occur too early to be visible from Coventry, but luckily that was not the case and we would be able to see the last hour, from sunrise at 04:47 BST through 3rd contact at 05:37 BST to the end of the transit at 05:54 BST.
That was how things stood until I was contemplating how to celebrate that other event in 2012, the diamond jubilee. No, not the queen’s, but my own on the same day. Then I suddenly realised, as the transit would occur in the early hours of June 6th, if I travelled sufficiently far west around the world, it would occur on the day before, June 5th. So then I could not only celebrate the transit on my birthday, but also I would not have to get up at such an early hour!
At first I thought Alaska would be the ideal location, as the whole of the transit would be visible, but as the chances of a clear sky were negligible, I decided on the west coast of Canada instead. Not knowing what I wanted to do there beyond seeing the transit, my travel agent suggested that I fly to Vancouver in British Columbia, stay there for three days, then take the ferry further west to Victoria on Vancouver Island to see the transit.
So that was why I was contemplating the totally overcast sky from my hotel room in Victoria at 9 o’clock on transit day. The day before had been no better as it had started with clouds obscuring a partial eclipse of the Moon. However, the transit itself was not due to start until 3:06 pm local time and it would still be in progress when the Sun set 6 hours later at 9:11pm, so there was still plenty of time for the clouds to clear.
Blue sky above the Victorian skyline
As my intention was to join the local branch of the Royal Canadian Astronomical Society in a public viewing event outside the museum in Victoria, I walked the short distance from my hotel to console myself with a tour around the parliament building next door. During the tour my spirits rose considerably as suddenly the Sun was to be seen streaming through its stained glass windows.
Sure enough, on emerging from the building, half the sky was completely clear of cloud and what was more, the remaining cloud was being blown to the east (towards Vancouver) by the fresh breeze. So much so that by 2:00pm there was not a cloud in the sky.
Due to airline weight restrictions I had not packed a heavy tripod and telescope, instead I had taken my lightest camera tripod and a home-made telescope. This telescope is one I made years ago from a 2” cemented doublet lens and a plastic drainpipe, which combined with a 1” eyepiece and a 2x Barlow lens, gave a really nice image of the Sun when projected onto a piece of paper.
I happened across a couple of likely looking astronomers outside the museum as the time of the transit approached. It turned out though that they were members of the public also waiting for the astronomers. A few minutes later we were not disappointed as one came along with his Meade refractor and solar filter. So after introducing myself, we pointed our telescopes towards the Sun and waited for the event to start.
I was convinced that first contact would be at 3:11pm, but the local astronomer insisted that it was 3:06pm. Sure enough, just after 3:06 I noticed a notch appear near the top of the Sun and the transit had begun. It turns out that I had the time for the wrong Victoria, the one for Victoria in Australia, not Canada! That did demonstrate though, how transits of Venus were used to determine the scale of the solar system by calculating the distance to Venus from just those differences in times.
Second contact Venus against an orange sun
Eventually, the notch in the Sun grew into a black dot, which was the silhouette of Venus against the bright disc of the Sun. At about 3:23pm we had second contact and while I was taking a picture of it projected onto my piece of paper, I noticed someone carrying one of those large broadcast style TV cameras on his shoulder, also taking a picture of the image from my telescope. He seemed quite happy, despite the paper wobbling in the breeze.
I was surprised to find when I was back home in the UK that it had appeared on the local TV station’s news bulletin about the transit!
Once the excitement of second contact was over we watched Venus slowly traverse the Sun’s disc while chatting to hundreds of interested locals (Victorians?) about what they could see. Each hour being marked by the deafening peals of the museum’s carillon above our heads.
Mark Edwards watched the transit with a gathering of astronomers in front of the carillon, Victoria, Canada
By the time the shadows had begun to lengthen and the Sun’s image had become decidedly orange in colour there were at least six telescopes plus my own and numerous eclipse glasses trained onto the Sun, eager to follow the transit for as long as possible.
At 8:42pm though, our first cloud of the day started to obscure the Sun’s disc. This cloud was the only one in the sky, but had decided to sit just above the hill that the Sun was due to set behind. For the next 13 minutes we saw glimpses of the transit through gaps in the cloud, until at 8:55pm, both cloud and hill won and the transit for us was over.
By Paritosh Maulik
The Moon is our nearest neighbour in the sky. It is not only a pretty object to look at with or without any optical aid, but it holds the record of the early history of the Earth. It does not have any mind altering effect on us, but it does have a big effect on our weather. We would not be here if the Moon was not. We shall look at the formation of the Moon and some of its physical features.
The comets, meteorites and cosmic dusts which formed the solar system over 4.5 billon years ago, have been analysed as well as lunar rocks. The indications are, these have changed very little since its formation. In order to understand the history of the formation of the solar system, we need to have a better knowledge of these bodies. Our nearest neighbour the Moon, has not changed much since its formation, whereas, geological activities and weathering has caused a lot of changes on the Earth. Better knowledge of the Moon would help us to find out the early history of the Earth and possibly of other terrestrial planets as well.
Astronauts have been to the Moon and have collected about half a tonne of rocks. These are still being examined to find out the origin of the Moon. By now we have reasonable knowledge of the Moon, so lets see what is our present knowledge of the Moon and then we shall discuss a couple of recent lunar missions.
What we know about the Moon
1) Density of the Moon is about 3.35g/cc, compared to about 5.54g/cc for the Earth. This indicates that the Moon does not have substantial iron core like the Earth.
2) In general, Moon rocks contain less volatile materials such as water than those of the terrestrial rocks, the reason being, perhaps the Moon’s rock went through a severe heating process and this may explain why, although the mineral on the Moon and the Earth are broadly similar, but not quite the same. The lunar rocks appear to contain minerals which formed at higher temperature.
3) Since the isotopes of oxygen are similar both on the Moon and the Earth, it is likely that the Earth and the Moon formed at the same distance from the Sun.
Possible theories of the formation of the Moon
1) The Fission theory: - Soon after the formation of the Earth, it was spinning rapidly and a segment of the Earth broke away and formed the Moon. The suggested site is the Pacific Ocean basin. This segment came from the Earth’s mantle, hence the similarity of the minerals. It but does not account for the extra heating process the lunar materials went through.
The Mantle, is the layer between the core (heavy matter) and the crust (lighter) matter of the Earth. The mantle of Earth is about 40 to 2900km thick and is of intermediate density.
2) Capture theory:- The Moon formed at another part of the solar system and due to some process it got trapped into the Earth's orbit. Somewhat different mineralogy of the lunar rocks may support the process, but it requires too much of coincidences to capture the Moon where it is now. This theory cannot explain the excessive heating of the lunar rocks.
3) Condensation theory:- Both the Earth and the Moon formed from the same dust cloud. If this was the case, them why does the Earth have an iron core, but not the Moon and we cannot explain the excessive heating of the lunar rocks.
4) Impact theory:- About a Mars size object impacted the young Earth at a glancing angle. This ejected a large volume of super heated material from the Earth and formed a disc. This disc eventually coalesced into the Moon. This explains that the Moon does not have a massive core, but rocky in nature and the rocks have been through a severe heating process.
Now this is the accepted theory of the formation of the Moon. Theoretical modelling of planet formation also suggested that at the later stages of planet formation such impacts were common.
Since the lunar rocks went through a severe heating process, and if this material contained any water, the heat should have evaporated most of the water. However, there are oddities. Some recent analysis suggests that some of the minerals collected by the Apollo 17 mission contains reasonable amount of water.
It may be argued that this water was carried to the Moon by icy comets or watery meteorites. Geological origins of these mineral does not support the scenario of water carrying comets or meteorites. Considering the fact that the Moon was so hot to start with, yet volatiles are not that much less compared to that of the Earth.
Structure of the Moon
Apollo astronauts carried out seismographic experiments on the Moon to understand the makeup of the structure beneath the surface. In such experiments, propagation of seismic waves though the Moon is analysed. The basic conclusions were
1) Moon has a layer structure like other terrestrial planets, Mercury, Venus, Earth and Mars. Such structures are produced when a molten mass solidifies and the layers separate according their density; the heavier materials sink to the bottom.
2) The innermost core is metallic and its diameter is about 1000km. It is mostly solid and therefore the Moon does not have any magnetism, while the magnetism of the Earth is due to its molten iron core. Above the inner core there is a 1000km thick silicate mantle. The outer crust facing the Earth is 30 – 45km thick and the side away from the Earth is about 10 – 15km thick.
From Earth, some areas of the lunar surface appear dark while some are bright. The dark areas are relatively smooth and are made from basalt, solidified lava flow, formed a few billion years ago. These areas are called maria (sea). The lighter areas are much older and full of craters of various sizes. These areas are known as tarre (highlands).
Geology of the Moon
From seismic experiments it appears that, the core of the Moon may be molten. At present the Moon has hardly any magnetism, but the signature of the lunar rocks indicates that there was some magnetism in the past. Geological activities such as volcanism or Moonquakes have all but ceased. The only seismic activity on the Moon now is due to the tidal pull of the Earth.
When the Moon formed about 4.6 billion years ago, it was bombarded by meteors, left over from the formation of the early Solar System. This intense bombardment caused about upper 100km of the surface to become molten and it remained so for about 600 million years. As this molten surface began to solidify, the rocks began to settle down according to their density. This is called differentiation.
The fracture and the melting of the surface triggered volcanism and continued from 3.8 to 3.1 billion years ago. By then, the most of the debris of the Solar System had been captured and planets formed; meteor activity on the lunar surface has slowed down.
Lava from the volcanoes flowed into the low laying areas and during this process a lot of craters also got covered; only the very big craters remained uncovered. The highland areas were not covered by the lava flow and still today bear the witness of the meteor activity as craters. Since the highland areas were not subjected to any geological activities these represent the early stages of the formation of the both Earth and the Moon.
Lunar far side, image taken by Moon Reconnaissance Mission, NASA
The Soviet Luna 3 probe in 1959 was the first to image the far side of the Moon and then the US missions took higher resolution images. The far side is mainly cratered and very little is maria or flat land. One of the explanations is the heat sources were on the near side of the Moon and there were more irruptions. Another explanation is, the Earth protected the near side of the Moon from meteor bombardment and since there was no such protection on the far side, more bombardment occurred on the far side covering it with craters. The Earth also shields the near side of the Moon from the Solar wind and there is higher concentration of helium (He3). It has been suggested that this could be a potential fuel for fusion reactors.
The bright appearance, or albedo (Latin whiteness), of the lunar surface is due the impact of the meteorites. Then space weathering causes such bright areas to get darker with time and the albedo decreases. Meteor impact erosions also alter the features of the craters and the formation of a later crater can cover another earlier crater.
The Earth and the Moon
By the time the Moon has gone through one rotation about its axis, it has completed one revolution around the Earth as well. This is the reason that we see on the same face of the moon all the time. The Moon is said to be in synchronous orbit with the Earth, that is, the Period of Rotation is same the Period of Revolution
Due to the tidal locking, only the near side is visible to us, but the invisible side is not dark, it sees the Sun; it is also a radio blackout area from the Earth. Hence sometimes the far side is called dark side, but it is in fact a radio “dark” side. During librations, the wobble of the Moon, we can see about 8% of the far side. Since the far side of the Moon is radio dark, it has been suggested that it could be ideal site for radio telescopes; however the lunar dust could be a serious problem for such a venture.
Effect of Magnetic field on the Moon
Although the Moon does not have its own magnetic field, it can come under the magnetotail of the Earth. The influence of the magnetic field of the Earth extends far beyond Earth.
This magnetic field takes an elongated shape due to the solar wind and in the direction of the wind away from the Sun. It is called a magnetotail and is full of hot charged particles (plasma). The sunlight charged particles, the electrons bombard the surface of the Moon and the Moon gets negatively charged. On the dayside of the Moon, the ultraviolet photons from the Sun interact with the electrons and majority of the electrons leave the surface and the build-up of charge is kept at a relatively lower level. But, on the night side the charge level can build up to a very high level. This can lift the dust particles from the surface and can produce a nasty shock. Some satellite images of the moon have shown such a dust cloud (for further details see
Tidal force on Moon
The gravitational effect on the Earth by the Moon causes deformation. This deformation causes by the large volume of water on the surface of the Earth to rise as a tide. Earth being more massive than the Moon, the gravitational effect of the Earth on the Moon is much higher; about 20 times more than the Moon’s effect on the Earth today. Soon after the formation, the moon was about 1/10th of the present distance from the Earth. The present average Earth – Moon distance is 384,400km. The early stronger tidal force of the Earth on the Moon is likely to have caused the Moon to elongate toward the equator of the Earth. Being hot soon after its formation, the Moon was softer as well; a soft Moon was easy to deform. Soon after its formation, the Moon was rotating fast and was closer to the Earth. Then with time the centrifugal force due to this rotation caused Moon to move further away. About 400 million years ago during the Devonian period, the Earth was also rotating faster. The day used to be 21 hours long and there were 460 days in a year. This is being corroborated by the daily growth ring of Devonian fossil coral Pleurodictyum. There are approximately 400 growth rings on this coral.
The Apache Point observatory in Texas measures the Earth – Moon distance daily by Laser Ranging method. A Laser beam is fired at the Moon. The laser light is reflected back by reflectors left on the Moon by the Apollo missions. Most of the photons of the beam get lost and only a few return. This measurement is not that straightforward. Imagine that the Earth is stationary and the Moon is rotating. The beams reflected from the surface of the Moon undergo Doppler shift. The surface approaching the Earth causes blue shift and there is red shift from the receding side. Therefore the frequency of the transmitted beam is not the same as that of the reflected beam. By now the observatory has collected about 40 years of data. The Moon is receding from the earth by about 3.78cm per year.
The fast rotation of the Earth gives it stability or rotation. As the Moon moves further away from us the Earth rotation will slow down; as a result the weather patterns on the Earth would be unstable; for example, the Polar Regions will see longer winter and the massive ice build-up, whereas away from the Pole it will be baking hot. As the season change, the polar ice will melt and oceans will rise leading to flooding of wide spread areas. For the areas away from the Poles, it will be longer and much cooler winters. However this futuristic dooms day scenario will not occur for another hundreds of millions of years yet.
Currently the Earth – Moon distance is about 400 times the Earth – Sun distance and the Moon is about 400 times smaller than the Sun. This allows the total eclipse of the Sun, but as the Moon moves further away from the Earth, we would lose the phenomenon of the total eclipse. The Earth is in the Goldilocks zone from the Sun. The comets brought water to the Earth, but the Moon caused the tides; coastal regions alternate from wet and dry areas and it may be that the life began in the inter-tidal zone.
The Moon, our nearest astronomical neighbour, a segment of the Earth, holds the record or part of it, of the formation of the Earth. We owe our predictable weather to a large extent to the Moon. If the Moon was not there, life on the Earth might not have survived.
A Couple of Recent Lunar Missions
There have been many missions to the Moon, both unmanned and manned. Rock samples have been bought back, but there remains plenty of unknowns. Here we shall look at two recent Lunar missions
The solar system as been up and running for about 4.5 billion years. All terrestrial planets have undergone changes; this makes it difficult to understand the early evolution of terrestrial planets. The Lunar rock samples brought back to Earth suggests that there has been very little changes on the Moon and also the Moon is the “easily accessible”. Therefore the Moon is an ideal place to understand the early geological history.
Chandrayaan–1 India Space Research Organisation
In October 2008, Indian Space research Organisation sent its first lunar mission, Chandrayaan-1 to the Moon. It carried instruments from several different countries. It was to operate for two years, but suffered a premature failure, but on the whole, it was a mixed success.
The mission carried a Moon Impactor Probe to find a suitable landing site for the future mission. A projector was released about 100km away from the surface and as it fell, it recorded and sent information back to Earth via a satellite. Data from this probe detected the presence of water in the lunar soil.
A NASA instrument called Moon Mineralogy Mapper (M3) has identified some iron bearing minerals.
During its 3,000 orbits around the Moon, 70,000 images were collected. Some of the images were about 5m resolution. It also detected the landing sites of the Apollo missions. It also captured the full image of the Earth.
X-ray imaging: A solar flare caused x-ray fluorescence of aluminium, magnesium, and silicon. This was detected by the x-ray camera.
During the mission the spacecraft began to sense higher than expected temperatures. This was partly corrected by altering the angle to reduce the heat received from the Sun and switching off some of the instruments. But it did not quite solve the problem. The root cause of the high temperature was radiation from the Sun and infrared radiation reflected from the lunar surface.
During this period, the spacecraft was orbiting at an altitude of 100km. Then the craft was raised to an altitude of 200km. This allowed it to study perturbation of the orbit, variation of the gravity field of the Moon and imaging over large areas. It was hoped that the higher orbit would keep the temperature low. Originally the system assumed that the temperature would be 75°C at 100km altitude, but in reality it was operating at a higher temperature and this was perhaps the major cause of the failure.
Then there was a setback. There were two altitude detecting systems, taking bearings from the star, failed. Then spacecraft guidance was transferred to the backup system which operated with taking the reading from the Sun and a ground station. This was partially successful. Some of the instruments were partially damaged earlier and radiation from the Sun also added to further failure.
A radar system called Miniature – Synthetic Aperture Radar was on board. This instrument is capable of distinguishing water ice from other form of water. The results from this instrument were only partially successful. It looked at more than 40 darkened craters near the North Pole of the Moon. It could not estimate the total quantity of water, but concluded that the ice must be very pure and reasonably thick such that the radar could pick up the signal. It may also be possible that the water may not be present as liquid water, but may be mixed with rocks.
Chandrayaan -1 mission carried an instrument called SARA (Sub keV Atom Reflecting Analyser) developed by European Space Agency and Indian Space Research Organisation. Its aim was to study the interaction between the solar wind and the Lunar surface. It was expected that the hydrogen nuclei in the Solar wind would react with the oxygen in the lunar minerals and would produce a compound like hydroxyl (OH) and water (H2O). The results were somewhat a surprise. One out of 5 hydrogen nuclei was not absorbed and escaped the weak lunar gravity and rebounded to the space as a hydrogen molecule. These early results were useful information for the future ESA Bepi Colombo mission to Mercury, which would be carrying two similar instruments.
The mission was launched on 29th October 2008 and was scheduled to operate for two years, but the communication was lost after nearly ten months (312 days). The likely cause of the failure was overheating damaged the power supply.
For details of the mission see
NASA launched its GRAIL (Gravity Recovery And Interior Laboratory) mission in September 2010. Its aim is to understand the geology of the Moon by high resolution gravity mapping; resolution better than 10 mGal in grids of 30 x 30km. 1 Gal or Galileo is the measure of acceleration and is defined in SI units as 0.01 m/s2; a mGal is 1g.
The flight to the Moon took three months. It was launched in September and arrived in the lunar orbit in December; the Apollo missions on the other hand took only three days to reach the Moon. The slow journey was chosen to reduce the fuel requirement, to protect the instruments and to enter the lunar orbit at a slower speed. Once in the lunar orbit, two near identical spacecrafts, named Ebb and Flow, each about the size of washing machines, weighing about 200kg each, were released at 24 hour intervals. These two crafts orbit the Moon in formation, in a near elliptical polar orbit in 11.5 hours. The distance of separation between two crafts is maintained between 175 – 225km and for high resolution gravity mapping the crafts are maintained at an altitude of 50km. All these tight requirements meant that the launch window was one second and there were only two possible launch times in one day. Any deviation between the distance of separation of the spacecrafts is due to the localised variation of the Lunar gravity and from this data a gravity map of the moon is drawn.
The major aims of the mission are to understand
1) The crust and the lithosphere; lithosphere is the slab under the crust.
2) Since its fiery formation, the Moon did not cool uniformly.
3) Localised areas of the Moon appear to show higher gravity, possibly due to high mass concentration and hence name MASCON's. Try to get a better understanding
4) Formation of larger rocks from the assembly of smaller rocks.
5) Lunar magnetism.
6) Effect of tide due to Earth on the moon.
7) Estimation of the size of the lunar core.
There are basically two major instruments in the system,
1) Lunar Gravity Ranging System (LGRS) This instrument is responsible for monitoring the distance between the two orbiters and converts the distance signal into gravity variation. This data is then sent to the ground station. This concept was originally developed for the NASA - German GRACE mission for the gravity mapping of the Earth.
2) MoonKAM (Moon Knowledge Acquired by Middle school students) Its aim is to image the Moon for students and outreach.
The mission gathered more than about 99.9% of the scientific information related to lunar crust to core in a time less than originally anticipated. Originally, the mission was to operate between two lunar eclipses. During the eclipse there will darkness to operate solar panels and drop in temperature. But, the performance of the mission so far has given enough confidence to extend the mission. The crafts would be lowered to an altitude of 23km to plot an even higher resolution gravity map. These crafts would clear the highest features by only about 8 km. The current plan is to continue the mission during 30th August to 3rd December, 2012.
For more information about GRAIL