Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.armaghplanet.com/pdf/Astronotes/Astronotes2008/Astronotes_Mar_2008.pdf Дата изменения: Tue Sep 20 18:49:13 2011 Дата индексирования: Tue Oct 2 01:26:41 2012 Кодировка: Поисковые слова: x-ray background

March 2008

ASTRONOTES
Incorporating FRIENDS' NEWSLETTER The Light Fantastic Can I really see the Moon during the day? The Night Sky in March Life on Mars Is space tourism too dangerous?

ARMAGHPLANETARIUM


2 Astronotes March 2008

The Light Fantastic
Image Credit: Deborah S Krolls

All the colours of the rainbow as revealed by Isaac Newton's experiment of projecting white light through a prism. Indigo, a relatively obscure tone, is included only because Newton, deeply interested in the occult, thought that there should be seven colours in the rainbow as he thought 7 was a number of mystical significance.

oscillating together through space. Hold this image in your mind- I'm going to flatly contradict it in a moment or two. Every EM wave has a frequency (how often per second it wobbles) and a wavelength (how far it travels between wobbles). These are linked; a high frequency EM wave will have a short wavelength while a low frequency wave will have a long wavelength. For example, the waves carrying the data to your computer in a domestic wireless network may be buzzing away more than two billion times per second (2GHz) and have wavelengths about 15 cm (6 inches) long. (Try multiplying two billion by 15cm, you will get a speed in cm/s; turn it into km/s. Does the answer look familiar?) In contrast, a broadcast radio station may transmit the news and music at 96 MHz (i.e. 96 million oscillations per second) in waves 3m or so long. (Try that multiplication thing again.)

By Colin Johnston, Science Communicator Before the modern era of technological astronomy, to know anything about the Universe beyond our planet we relied on light. We had to see planets, stars, and so on, to know they existed. Astronomy was based entirely on light. What then is light? This is a question which occupied the minds of some of the greatest scientists. Many early ideas have been discarded, now we have a good idea of the nature of light. Historically the two rival ideas were that light was either a stream of tiny bullet-like particles or a wave wobbling its way through space. The light we see (visible light which is not the tautology it sounds) is only part of the electromagnetic spectrum, a great sweep of radiations which also includes radio, infra-red, ultra-violet, x-rays and gamma rays. This is the celebrated Electromagnetic Spectrum. Unlike sound, all electromagnetic radiation can travel through completely empty space at about 300 000 km/s (186 000 miles per second), the fastest speed possible. Any electromagnetic radiation does indeed travel in the form of waves. The obvious question is "waves in what?" and the least-complicated but rather unsatisfying answer is "in itself". An electromagnetic (EM) wave is a pair of co-joined electric and magnetic waves

"electromagnetic radiation does indeed travel in the form of waves "
The EM spectrum discriminates radiations by their wavelength or frequencies. Let us take a walk through the spectrum. Radio waves are relatively long wavelength (the Extremely Low Frequency signals used to communicate with submerged submarines are 3000-6000 km long!). Shorter wavelength (say 1m to 1 mm) radio waves are termed microwaves (look at the back of your microwave oven; you ought to find the microwave frequency in MHz somewhere), shorter still waves include the infra-red bands and then in the middle of the spectrum we have the familiar ROYGBIV (Red, Orange, Yellow, Green, Blue, Indigo, Violet) which Isaac Newton showed to make up white light. This is the `proper' light we are all


March 2008 Astronotes 3

The long and the short of it Electromagnetic waves from radio to gamma rays. familiar with, most of the Sun's radiation falls in this comparatively narrow band of wavelengths. Green light (in the centre of the visible band) has a wavelength of about 0.00055mm about 1/10 the diameter of a red blood cell. Moving beyond violet, we pass into the invisible ultra-violet, as the waves shorten we enter the realm of X-rays and gamma rays. suggested strongly that light was actually a stream of tiny particles after all. It was for pointing out this explanation that Einstein was awarded his Nobel Prize rather than his better-known theories of Relativity. The particles were even named photons. So light is either a wave or light is a stream of particles. Which is the right answer? Again the answer, derived from quantum mechanics (a can of worms I have no intention of delving into here) seems an unsatisfying cop-out. Light is both at the same time. Weird though this may seem, something can be a wave and particle at once (although this can only be observed on very small scales). Astronomers are accustomed to this. You will read about, say, a telescope designed to focus gamma ray wavelengths on to a detector which counts the number of photons it picks up. In future Astronotes we will examine just how scientists pursue astronomy outside the visible wavelengths.

"By the start of the Twentieth Century it was certain that light was a wave."
By the start of the Twentieth Century it was certain that light was a wave. Many experiments confirmed it. Then some experiments indicated that a beam of light shining on a metal surface could knock electrons out of the metal. This was inexplicable by the wave theory, in fact it

Can I really see the moon during the day?
By Paul O'Neill, Education Support Officer Working in a Planetarium leads to you being asked all manner of queries from those puzzled by the Universe beyond. Here is just a sample of questions I have been asked. Can I see the moon during the day?

Image Credit: NASA


4 Astronotes March 2008 the case of exo-planets). Is Astrology the same as Astronomy?
Image Credit: © Henry Firus, Flagstaffotos

No. Astronomy (also called science with strong links to is the belief that stars have our lives and personalities. science. Is space hot or cold? The Moon over cumulus clouds photographed in daytime Yes you can ­ kind of. We can see the moon because it reflects a small part of the sunlight which falls on its surface. It's all about contrast. Usually during the day the sky is so bright that the small amount of light from the moon is drowned out; while at night it appears bright because the sky is so dark. Sometimes you can see the moon in the morning or late afternoon sky because there is still enough contrast. The same is true for stars but since they are even dimmer we need quite a dark sky to see them. Does the moon have a dark side? No it doesn't. Gravity has `locked' the Moon in such a way that from Earth we only ever see one side of it but the far side of the moon does receive the same amount of sunlight as the near side. It is not dark. Why do stars twinkle? Actually the stars themselves don't twinkle. They appear to because their light gets disturbed by turbulence as it passes through the Earth's atmosphere. This random movement in the atmosphere causes the star's light to be bounced around in such a way as to give an illusion of twinkling. Are planets the same as stars? No. Stars are massive balls of very hot gas which produce their own light. Planets are either balls of rock and metal like the Earth or larger balls of cold gas like the planet Jupiter. Planets do not produce light; we can only see them because they reflect the light from the sun (or other star in

Astrophysics) is a physics. Astrology an influence over Astrology is not a

The answer is neither. Space is a vacuum ­that is empty space - and so does not have a temperature. Only matter and radiation can have a temperature. What is a light year? It's not a measurement of time, it's a distance. In a vacuum light travels at 300 000 km (186 000 miles) per second. There are 60 seconds in a minute, 60 minutes in an hour and of course 24 hours in a day; so 24 hours equals 85,400 seconds and one year equals 31,536,000 seconds. This means that at roughly 300 000 km per

The far side of the Moon photographed with Apollo 16's mapping camera. We can see the eastern edge of the familiar near side at the left and the strange and heavily cratered far side of the Moon. Lacking the nearside' s familiar dark seas or maria, the far side looks very different from the near side (but it isn't dark).

Image Credit: NASA


March 2008 Astronotes 5 of these images are useful for imagining a black hole. A star is a massive ball of extremely hot gas; deep in its core thermonuclear reactions (like exploding H-bombs) are trying to blow the star apart; but the equally powerful force of gravity is trying to crush the star. When the star runs out of fuel gravity takes over causing all the gas to collapse in on itself. For a star like our Sun the result is a white dwarf ­ the material is so dense a pinhead amount of it would weigh more than a super tanker. For stars much larger than our sun the collapsing process goes out of control ­ producing an object so small yet so dense its gravity sucks in everything ­ even light. This object is a black hole.

Image Credits: NASA/JPL-Caltech

A supermassive black hole at the centre of a galaxy. The blue colour in this artist's impression represents radiation pouring out from material very close to the black hole. The greyish structure surrounding the black hole is made up of gas and dust. second light travels a staggering 9 460 800 000 000 km (5 879 000 000 000 miles) in one year; this distance equals one light year. Many of the bright stars you can see in the night sky are tens or hundreds of light years away.

Could a comet or asteroid hit the Earth? Yes it could; in fact it almost certainly will. The effects may well be devastating for humanity. Chances are the object will hit one of the oceans (because they cover the majority of the Earth's surface). The resulting tsunami will have enough power to annihilate several cities. The immediate death toll might be hundreds of thousands with millions more made homeless. A `nuclear winter' could result from the impact causing famines and extreme weather conditions. One or two decades ago governments did not take this threat to our survival seriously but now some are beginning to take notice.

What is a black hole? When we think of a hole we imagine a hole in the ground, in a wall, in your pocket etc. None

The Night Sky in March
By Colin Johnston, Science Communicator I like asterisms. These prominent patterns of stars are often easier to see and point out than constellations. Not only that, they usually encompass several constellations. Once you have found the asterism, you have found the constellation, this can be useful in a sky murky with light pollution. At this time of the year, the southern sky is dominated by a huge asterism called the Winter Circle. This is made of stars from Auriga (the Charioteer), Taurus (the bull), Orion (the Hunter), his dogs (Canis Major and Minor) and Gemini (the Twins). Starting at the top of the circle we have Capella in Auriga. Capella (the Little Goat) is 42 light years (12.9 parsecs) away, meaning the light we see from it now left there in 1966. Capella is actually a binary star system of two giant G-class stars. These orbit one another so tightly that it is difficult to separate them in a telescope. Both are running out of hydrogen and are leaving the Main Sequence. Before long they will swell into bloated red giants.


6 Astronotes March 2008 cooler than the sun's. An aging star, Aldebaran has completely left the Main Sequence and burns helium rather than hydrogen in the centre of its nuclear furnace. Rigel is at the `five o'clock' position in the Circle. Blue-white Rigel is a B-class supergiant star. Tens of thousands of times brighter than the Sun, it is one of the brightest stars in this region of the Milky Way, only Deneb is more luminous. We are not quite sure just how bright Rigel is because we are not sure how far away The Winter Circle encloses Orion and passes through other several promi- it is but it seems to be somewhere between 700 nent constellations. It also passes through the relatively obscure constellaand 900 light years away tion of Monoceros (the Unicorn). Note the Pleiades outside the circle at the (215-275 parsecs). Rigel extreme right. is part of a trinary system Moving clockwise, the next star is Aldebaran (the of stars; a pair of companion stars, both B-class, Follower), the brightest star in Taurus. Aldebaran, orbit it too. Rigel is part of the extremely easy to a K-class giant star appears distinctly orange. identify constellation of Orion If you look closely you will see a scattering of stars around Aldebaran. This is the Hyades star cluster, but Aldebaran is not part of this grouping. Aldebaran is 66.7 light years (20.4 parsecs) away while the cluster is more than twice as far away at about 151 light years (46.3 parsecs). The star appears orange because its surface is

Image Credit: Colin Johnston , Science Communicator (Image created with Starry Night software)

"... African people called the Dogon knew about Sirius B long before Europeans "

Rigel a blue supergiant star, viewed from a distance of 1AU in this artist's impression. Note the sunspots.

Sirius, the Dog Star (appropriately enough it is a member of Canis Major), lies lowest in the Circle. This is, of course, the brightest night time star. It is bright because it actually is unusually bright; more than twenty times as bright as the Sun and it is close, only 8.6 light years (2.6 parsecs) away. Sirius has a companion white dwarf star (the Pup) which is visible only to large telescopes. This faint little star was first observed in the 1860s, but in the 1970s writer Robert Temple popularised the idea that members of an African

Image Credit: Will Fox


March 2008 Astronotes 7 ish-coloured F class star is about half again as massive as the Sun but about 7 times or more as bright. Like Sirius, Procyon also has a faint white dwarf as a companion.

Image Credit: NASA, ESA, H. Bond (STScI) and M. Barstow (University of Leicester)

"... why not go outside and see if you can find this giant wheel in the sky? "
We finish the Circle with Pollux and Castor in Gemini. These stars are in no way identical twins. Pollux is a single giant K-class star about 34 light years (10.7 parsecs) from Earth. It is a yellowish orange in colour and is orbited by a planet more than twice as big as Jupiter. Castor, a very hot white A-class star is about 50 light years (15.3 parsecs) away. Castor is a member of a sextuple star system. This is not as racy as it sounds; it means that Castor is one of six individual stars bound together by gravity (the other five are too dim to be seen with naked eye). If tonight is a nice night, why not put on your hat and coat, go outside and see if you can find this giant wheel in the sky and show it to your friends!

Sirius A as seen by the Hubble Space Telescope The faint, white dwarf companion, Sirius B is just visible in this over exposed image. The cross-shaped diffraction spikes and rings around the stars are artifacts produced within the telescope's imaging system. people called the Dogon knew about the Pup long before that. Had the Dogon's ancestors learnt this first-hand from space travellers from Sirius? Thanks to Temple's sober style, this idea was treated with rather more seriousness than it really deserved, but is not believed to be correct today. Next we have Procyon in the remarkably uncanine-looking constellation Canis Minor. At just 11.4 light years (3.5 parsecs) away Procyon, like Sirius is a near neighbour of the Sun's. A whit-

Moon Phases, Mar 2008
Fri 7 March Fri 14 March Fri 21 March Sat 29 March NEW MOON First Quarter FULL MOON Last Quarter

Life on Mars?
By Alyson Kerr, Education Support Officer One of the biggest news stories last month concerned the `sighting' of a humanoid figure on the Martian landscape. Once again, the world's media blew it out of proportion. Despite their willingness to lead you to believe otherwise, it was not a first encounter with an alien life form but a rock that slightly resembled a humanoid figure. The pictures in question were taken by NASA's Mars Exploration Rover, Spirit. The image is actually a small part of a large panorama of the West Valley taken last September. Spirit is looking westwards from its position on top of


8 Astronotes March 2008 Home plate, past the Columbia Hills on the right, towards its original landing site. The conspiratorial rock is little more than five metres away from the camera and is certainly a `giant' at approximately 10cm (4 inches) tall. course, have been frozen in place by the subfreezing Martian temperatures (-55 °C on average) but this would mean that we would have an incredibly small, cold, and probably dead Martian on our hands. Humans have always had a propensity for seeing things that aren't really there, giving significance to insignificant patterns, this is called Pareidolia. Stories of images of religious icons appearing in food or on textiles are commonplace in society so it is not surprising that this is now transferred to Mars.

Image Credit: NASA

Bigfoot on Mars This is the innocent rock that is causing all the commotion. It has been likened to past images of `Bigfoot', as well as the statue of the Little Mermaid in Copenhagen. While it does have an obvious human shape, it is still quite obviously a rock. This seemingly innocent photograph has stirred up the age old debate about life on Mars with some people looking past the facts and using this as the proof. Let's take a moment to look at the facts. The Spirit Rover actually took a series of images of the same panorama with different filters on the camera, so our alien friend was either incredibly patient to hold the same pose for the six minutes it took to capture the images or he is, let's say, a rock? He could, of

"If there was life on Mars ...surely we would have found it by now"
As an exciting and extraordinary place that we are still learning about, the imagination can run wild, but we must learn to see the truth. If there was life on Mars, especially life more significant than bacteria, surely we would have found it by now. Opportunity and Spirit have been exploring the Martian surface for four years and have not encountered life, nor did we expect them to. Any life that may be discovered will be in the most basic form rather than a walking, talking humanoid (even a small one). Mars has so much to offer as we explore it, focusing on the science rather than the fiction is the way forward!

Two Good Reads
By Coin Johnston, Science Communicator Anyone interested in the possibilities of life elsewhere in the Universe, will enjoy Surendra Verma's `Why aren't they here?' In a chatty narrative (which occasionally rambles a little too far off course) the book discusses theories about extraterrestrial life from those of Aristotle up to the recent dubious reports of alien microbes descending in red rain in lndia. Sadly the publishers have neglected the editing and proofreading processes; there are occasional obvious howlers but I would not be put off by this. It is a thought provoking read which leaves the titular question open but suggests many possible answers. `The Cloudspotter's Guide' is not really astronomy, being a discourse on those fuzzy grey things which all too often hide the night time sky from


March 2008 Astronotes 9 us. I found reading it to be an education. Once, I couldn't tell altocumulus from cirrostratus but this book has given me a whole new appreciation of the many types of clouds and their role in our atmosphere. Rather than ignoring or even abhorring clouds I can now relish (and identify) their varied forms and appreciate their majesty. Illustrated with photographs, charts and fascinating anecdotes, this is certainly the wittiest nonfiction book I have read in ages. You can learn a lot from it too; perhaps even how to predict a clear sky. `Why aren't they here?' by Surendra Verma, Icon Books, 2007, ISBN-13:978-1840468-06-9

`The Cloudspotter's Guide' by Gavin Pretor-Pinney, Sceptre, 2007, ISBN 9780340895900

A not so giant leap for mankind?

Image Credit: © Virgin Galactic

Flying into the Future Scaled Composites' designs are truly magnificent vehicles and the company is not afraid of unorthodox layouts. White Knight two's unusual twin fuselage layout has not been used for a production aircraft since the 1940s vintage He111Z and P-82 Twin Mustang. Opinion Piece by Colin Johnston, Science Communicator With great fanfare, space tourism company Virgin Galactic has unveiled the vehicles their fare-paying passengers will ride in as they ascend into space. Built by the supremely adventurous company Scaled Composites, the pair are engineering marvels. The huge yet elegant White Knight Two jet aircraft has a 43 m (141

Image Credit: Amazon.co.uk


10 Astronotes March 2008 ft) wingspan. Its payload is the SpaceShipTwo spaceplane, a considerably larger offspring of the SpaceShipOne which won the Ansari XPrize in 2004. Observers were surprised to see that SpaceShipTwo is not a simple scale-up of its fish-shaped predecessor. It looks distinctly different, resembling more the 1960s X-20 (the cleverly named Dynasoar), a vehicle which was cancelled before it ever flew. If all goes well, in the near future a White Knight Two will carry a SpaceShipTwo spaceplane to an altitude of 15 km (9.3 miles) and release it. The SpaceShipTwo will fire its rocket and blaze upwards, reaching a peak altitude of 110 km (68 miles) before gliding home. The six passengers will have the time of their lives, enjoying a few minutes of micro-gravity and stunning views of the Earth. The age of routine spaceflight will finally have arrived. Hopefully.

Spaceship Two Like its prize-winning predecessor, the craft uses the patented feathered re-entry system. But is an experimental rocket plane ready to carry passengers? craft. The major aircraft building nations between 1940 and 1975 spent a lot of money researching rocket planes, including flying a series of experimental prototypes. Nazi Germany even put one into mass production. More than 400 bat-like Me 163s were built to defend the Third Reich from Allied bombers (although only a few dozen were used operationally). Yet SpaceShipTwo is the first production rocket plane in decades. Why? Part of the answer is that developments in jet engine technology sidelined the rocket as an aviation powerplant. However there was another important reason: rocket planes crashed very often. A liquid-fuelled rocket engine is a very complex piece of engineering with many components capable of potential failure. A rocket plane is full of very explosive propellants and flies at high speeds where any structural failure would bring disaster before any pilot can react. The Me 163 referred to above is said to have killed more German pilots in accidents than Allied aircrew in combat. Here are some numbers. They cover only rocket planes belonging to the UK and USA as those of other nations are not well-documented. In a thirty year period starting in 1947, just 16 rocket planes of six basic types made 499 flights (compared to thousands of jet aircraft making tens of thousands of flights). Ten of these aircraft were lost in crashes, five of them fatal. Two of these crashes can be attributed to pilot error and can be ignored. The rest were the result of technical problems with the rocket plane itself. These

"SpaceShipTwo will not fly into orbit or dock with the ISS"
Just to clear up a common misconception, SpaceShipTwo will not fly into orbit, nor can it dock with the ISS or any future orbital hotel. Limited to a maximum speed of 4000 km/h (2500 mph), it simply cannot reach the velocity of 28 000 km/h (17 400 mph) needed for a Low Earth Orbit (as one wit has pointed out Virgin Galactic passengers will not reach LEO, never mind LIBRA, VIRGO or any other constellation). An orbital vehicle could be designed to fit under White Knight Two, but to meet the weight considerations it would be of necessity a tiny, one-person pod, not unlike an early space capsule. Rather than holidays in space, Virgin Galactic is selling the ultimate in exciting but brief stunt flights in a rocket plane. My main reason for being sceptical about the claims of Virgin Galactic (and its rather insubstantial competitors) is the possible safety of rocket planes (or lack thereof). There once was a vogue for rocket-powered aircraft. Their speed, rate of climb and ability to attain great altitudes was superior to even jet air-

Image Credit: © Virgin Galactic


March 2008 Astronotes 11 figures indicate an accident rate of about 1 in 62! This risk may be acceptable for volunteer test pilots, but are fare paying passengers prepared to face it? Note also that this loss rate is almost exactly the same as that of the Space Shuttle (two fatal crashes in 120 flights) and the Shuttle's safety record is one of the reasons for its imminent retirement. been avoided thanks to lessons learned, but they were very specific to the designs of the vehicles involved. We do not have enough experience of rocket-powered craft operating at the edge of space. SpaceShipOne was retired after only three flights above 100km. Passenger aircraft must make thousands of test flights before they are certified. I am not sure that Scaled Composites can afford to do this with SpaceShipTwo. I am sorry to say this but sooner or later a space tourism craft will be lost and almost certainly passengers will be killed. What happens next? Our society is very safety conscious and the vehicle's owner will find themselves in court (remember only the very wealthy will be able to afford space tourism tickets ­ their relatives may be able to afford the sharpest lawyers). Rather as fear of being sued for malpractice has allegedly forced some doctors out of medicine, we may find space tourism companies shutting shop to avoid litigation.

"16 rocket planes made 499 flights ... ten of these aircraft were lost in crashes"
Perhaps this does not mean there are grounds for concern. Travel by conventional aircraft was once very dangerous, but nowadays by several yardsticks it is among the safest modes of transport. If a similar improvement to rocketpropelled aircraft has occurred - and I have no doubts that this is achievable - the safety of space tourists will be assured. However it is unclear if such improvement has happened. Sad to say, but the safety of modern Boeings and Airbuses is based in part on the lessons learned through thousands of air accidents. Some of the historical rocket plane accidents could have

"the first crash of a space tourism vehicle will do to spaceflight what the Hindenburg crash did for airship travel "
I very much hope that I am wrong but I suspect space tourism in the Virgin Galactic mode is a false dawn. I fear the first crash of a space tourism vehicle will do as much harm to commercial spaceflight as the Hindenburg crash did for travel by airship. (For a less gloomy prognosis, see my colleague Wendy McCorry's article `Holiday with the Stars' in the May 2007 issue of Astronotes.)

Image Credit: NASA

Rocket Plane Mishap NASA's X-15s were superb research aircraft. On 9 November 1962, an engine failure forced pilot Jack McKay to make an emergency landing in the second X-15. The aircraft's landing gear collapsed flipping the X-15 on its back. McKay's injuries eventually forced his retirement from NASA. The X-15 was repaired to fly again.

(In writing this piece I referred extensively to the excellent article `Rocket Plane Roulette' by Jeffrey F. Bell found at www.spacedaily.com/reports/Rocket_Plane_Roulette_999.html. However I am slightly less pessimistic than Dr Bell as I have included the relatively safe HL-10 and X-24 craft in the analysis of rocket plane accidents)


12 Astronotes March 2008

Image of the Month
Image Credit: ESA

This giant mirror will soon be launched into space by the European Space Agency. This is not to let our planet admire her beauty but to study the Universe throughout the infra-red wavelengths, including wavelengths never examined by any previous telescope. The mirror is part of the Herschel Space Observatory, an exciting new ESA mission that has been under development since 1982. Herschel will look at dust discs around stars where planets may be forming, young stars and proto-stars, ancient distant galaxies, and much more. Hershel may once again revolutionise our view of the Universe just as Hubble has done.

With a diameter of 3.5m (about 11.5 ft), this is the largest mirror ever flown in space. In comparison the Hubble Space Telescope's is 2.4 m (about 7.9 ft) across, so Herschel's mirror has over twice the area of Hubble's. It is hard to believe that this flawless mirror is made from twelve separate silicon carbide petals brazed together and coated with a reflective aluminium layer, forming a remarkably lightweight mirror. Herschel will be launched later this year. The Planck microwave background satellite will be sent into space on the same Ariane 5 booster. (Caption by Colin Johnston, Science Communicator)

www.armaghplanet.com
Astronotes, Incorporating Friends' Newsletter is published monthly by Armagh Planetarium, College Hill, Armagh, Co. Armagh BT61 9DB Tel: 02837 523689 Email: cj@armaghplanet.com Editor: Colin Johnston ©2008 Armagh Planetarium All rights reserved