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MIRA 107

Old Views, New Views
By Ivor Clarke

Above the Moon depicted in 1881 and the view from the Orbiter 2 space craft on 24 November 1966 of the 100 km Crater Copernicus, this was called the 'Picture of the Century'.
Below a painting by Chesley Bonestell of a view on Mars from the icy polar cap looking towards the setting sun and from the Curiosity Mars rover of Aeolis Mons and the Murray Buttes at the base of the central mountain in Gale crater in 2016.

When astronomy and observation is impossible on cold, wet or cloudy nights (and in the Land of Lockdown), then is the time to catch up on reading and rereading books which I'm sure we all have and collected over the years.  I'm sure too, that many of you will have many favourite books, from well thumbed star guides to great picture books of deep sky images and the planets and their moons.  One of the pleasures is just looking at the pictures in them; it's a rare astronomy book without pictures.  If you have any old books on astronomy then looking at these images, often drawn and painted yesteryear and comparing them to todays views.  How things have changed.
When you have been interested in astronomy as long as I have, it’s easy to have lots of “old” books.  Even ones printed 25 years ago can now be well out of date and if they contain illustrations and photographs, they can look old, soft and dated compared with todays images.  Just look at photographs of the planets from the 1950's and 60's taken with some of the best telescopes at that time and compare them to todays digital images, often shot by amateurs on telescopes readily on sale!  It was only in the early years of this century that digital astro photography took off.  So with some of my collection of books going back to 19th cent, you can see they can be very wrong indeed in the information portrayed in them.

The comet of 1858 which was called Donati's comet is the frontispiece from The Stars book of 1881 is a loverly engraving of an evening scene with a crescent Moon low in the sky is very striking and a beautiful phenomena.

The oldest books I have are a small pair of green books called Wonders of the Heavens from 1881, one volume is called the Sun, Moon and Planets and other The Stars.  Both are about 230 pages with 46 and 40 engravings in each.  No author is credited with these books.  In MIRA 83 I have a story on Old Astronomy and some of the engravings from these books are shown, like the one of a Lunar Landscape with its strange tall pinnacle like towers for mountains, which was the frontispiece from the Sun, Moon and Planets volume.  On such a surface no one could safely land and the stars are out shining brightly!
Not all the information in these books are wrong however, as the orbital periods and distance are not out by much, but the number of moons around the outer planets are miles out.  For instance Jupiter is credited with only 4 moons and Saturn 8.  Now over 60 are known in each planets retinue.  In The Stars volume almost all the galaxies and are called spiral nebula and named after whatever constellation they are in and none have a Messier number.  Other nebula such as globular clusters and planetary nebula are called by the constellation name too.  Indeed most of them look to our eyes as odd shapes, not at all like what we have become accustomed too.  Back then all the observations would have been made by eye and didn’t have the advantage we have of having long exposure colour photography to resolve the dim mists of gas and dust that fill the space unseen with the eye.

This engraving of the Andromeda galaxy, M31 (NGC224) is also from The Stars book.  All soft fuzzies, galaxies or gasses nebula was classed into the same category as "nebula" even when they were very different in size and appearance.  M31 and was considered in the late 19th century to be "as wholly wanting in stars."  It was described as "this oval and whitish appearance, which, very brilliant in the centre, grew paler towards the edge."  The two smaller elliptical satellite galaxies of M31, M32 (NGC221) and M110 (NGC205) are missing from the engraving.

The first book I had on astronomy as a child was from a second hand bookshop when on holiday in Margate, The Story of the Solar System by GF Chambers.  This was also Patrick Moore’s first astronomy book, printed in 1895 it came with 28 engravings.  The first chapter on the Sun was 40 pages long and when you realise that no one at that time had any idea how it could radiate so much energy for such a long time.  It was the observation of sunspots, prominences and other features that was covered in the chapter.  But they knew the size and volume as 1,305,000 times Earth’s and the distance, 93,000,000 miles.

Bonestell painted this for the The Conquest of Space book, the space ship was very similar to a rocket used in the film Destination Moon, produced by George Pal which came out in 1950.  The film had the backgrounds on the Moon painted by Bonestell.  This view of the V2 shaped rocket with wings in a crater on the Moon surrounded with high mountains was very like the film view.  On the Moon you don’t need wings on a rocket, they are just extra weight. 

Newer books followed; and one I really liked was The Conquest of Space, the text is by Willy Ley and paintings by Chesley Bonestell.  This was printed in 1952 and contains some of the most famous space artwork ever done.  Most of the paintings were done around 1948 and many of them used in articles in the American Life magazine.  The first part of the book contains paintings of a launch of a V2 type rocket to the Moon and views of the lunar surface from the windows of the rocket.  Along with a view of the V2 shaped rocket with wings in a crater on the Moon surrounded with high mountains.  On the Moon you don’t need wings on a rocket, they are just extra weight.

Two more paintings by Bonestell, left Saturn seen from the satellite Japetus, the moon is about half the size of our moon and around 2,210,000 miles from its planet.  Saturn lies above the belt stars of Orion.  Below is Mars from Deimos showing the south polar ice cap and the dark feature Syrtis major with a few canals.  Deimos orbits Mars at 12,500 miles in 1.25 days and with the very low gravity the 3 astronauts have to be careful that they don't jump off into space!

Other paintings in the book were of views of the planets from various moons and views of planetary landscapes.  He also did a wonderful view of Saturn from its satellite Japetus, these are still stunning paintings to see and when you realise these are 70 years old and 10 years before Sputnik!  He also painted Mars from Demos with three astronauts fooling about in the microscopic gravity with a gigantic Mars with a few canals and the polar icecap.  On the surface he painted a view down a straight a canal like feature disappearing into the distance.  They are nice paintings and he even had the colours checked by a professional astronomer.

One of Chesley Bonestell's best known paintings done around 1951/2 for the American magazine Life, is of a large wheel type space station with a solar collecting heating mirror along its top with a central bar with a space taxi docking port.  Also is a space plane which was a Von Braun designed supply ship and nearby and a space telescope.  The space station would be in a 2 hour orbit just over a 1,000 miles high.  Seen here above the Panama Canal with Cuba and Florida in the distance, note that the edge of the Earth is a sharp line compared with the view below of the International Space Station at 230 miles high in a 90 minute orbit over an icy cloudy seascape.

One of his best known paintings done around 1951/2, is of a wheel type space station with a Von Braun designed supply ship nearby and a space telescope in orbit just over a 1,000 miles above the Panama Canal with Cuba and Florida in the distance is a classic.
One of the problems artists have is visualising a scene if you don't understand what it is made of and how it's formed.  They have to imagine what it will look like in the lighting they think will be there at the time.  Where will the shadows be and the high lights?  Are the colours right?  They are trying to draw views with no reference pictures.  When Bonestell painted the Earth from orbit he made sure he got the coast lines correct but he had no idea of the colours which we now know exist in shots taken from orbit.  So he painted most of the land green as he thought it would look from orbit with a little cloud cover and the sea a uniform blue.  Both of these colours are correct in small areas, but with lots of other details and colour over the land areas.  But back in 1948/52 no-one had anyway of knowing otherwise.
Of cause it’s easy now to pick holes in these pictures, now we have all seen photographs from orbit and from on the lunar surface as well as Mars.  But back in the late 40’s and early 50’s no one had seen the Earth from space and could not have released the wonderful colours seen from orbit.  Also at 1,000 miles high it was in a radiation zone from the Van Alan belts.
As science progress and we go further out into the solar system we will see more wonders from our space craft that will surprise us.  So spare a thought for the astro artist who goes there before trying to depict the scene, no wonder we all have enjoyed the journey.

Seeing the Unseen
or Peaking/Peering through the Dark/Cloud and Dust

By Paritosh Maulik

Optical images of astronomical objects often shows dark areas.  Dust and cloud block star light and cause these dark regions.  Nebulae are collection of gas and dust.  Radiation from a star makes some of the regions glow.  Star light also gets reflected and scattered by this cloud. Nebulae are the birth places of stars and planets.  These nebulae are very cold regions, the apparent empty space is full of interstellar dust.  Optical images give only partial information about the details of nebulae and dust.  Colder nebulae can emit radiation in infrared and radio wavelengths.  By observing in infrared and radio range we can learn about the detailed processes occurring in the gas cloud.

The temperature range of astronomical sources can vary from 106 to 101 K.  Anything above 0 K radiate electromagnetic energy

100% opacity means, nothing gets through.  X-ray and gamma rays (short wavelength) are absorbed by the atmosphere and can only be observed from above the atmosphere in space borne telescopes; in the range of 0.01 to 10 nano metre (nm), (3×1016Hz to 3×1019Hz).  Visible light, 400nm (4 x10-7m, violet) to 700 nm (7 x 10-7m, red), is less affected by the atmosphere and can be observed from ground level and as well as from space.  Space borne telescopes are less prone to the disturbances due to the atmospheric dust and temperature variation.  This is a rather narrow wavelength range.  Observation in near infrared can be carried out from very dry areas; telescopes above the cloud level, such as Hawaii, Chile and the Canary Islands.  Earth's atmosphere is largely transparent to a wide band of radiation in the range of millimetre to radio wave (about 1mm to 10m), and can be observed from the ground, but a drier location with low precipitation level is preferred for the observation in the millimetre range.  For the observation in the far infrared range, we have to use space borne instruments.

Why should we observe in the long wavelength range and What's special about it?
Stars like red giant, eject materials by radiation pressure or stellar wind.  Stellar explosions can also eject material.  With time, these accumulate in the relatively cooler temperature of the interstellar medium either as carbon or silicate grains.  These grains further accumulate elements like hydrogen, oxygen, carbon, nitrogen.  Eventually an icy mantle consisting of water ice, methane, carbon monoxide, ammonia forms around these grains.

This is a plot of opacity or obscuration, versus wavelet plot (wavelength in logarithmic scale).  Some of these radiations are absorbed by the atmosphere and do not reach the Earth.

Under the action of UV radiation from stars, a layer of organic compound develops over the outside.  
The size of these dust grains are comparable to the wavelength of UV (10 – 400 nm) to blue light 450 -495 nm) and are more like soot from a candle flame.  As a result, the light scattered from these grains is mainly blue.  This is why the reflection nebula appear blue.  However blue light is predominantly absorbed by these grains and the light transmitted by these grains is mainly in the red range of the spectrum, making the grins appear reddish.  
Although the dust grains amounts to only about 1% of the mass of the interstellar medium, these play a major role in the star formation.
1) In the rarefied environment of the interstellar medium, atoms may not interact with each other, but the surface of these grains can act as meeting sites of atoms and can form molecules.  Some of the energy of collision is used up in formation of molecules and some of it are absorbed by the dust grain.
2) Ionised gas is difficult to collapse under gravity.  UV radiation may ionise some, but not all of the molecules on the dust grain and the grains absorb some energy of the radiation.  Thus the grains reduce the overall ionisation.  In this way dust  gains helps gravitational collapse of gasses to form stars.
3) Interstellar dust absorbs the energy of collision and and absorbs some of the UV radiation.  As a result the overall temperature of the gas cloud is kept low.  Grains emit the excess energy as infrared and if the gas cloud is transparent to the infrared radiation, the temperature is maintained low; this helps gravitational collapse.
The most abundant gas in the interstellar medium is hydrogen and the typical temperature of the gas cloud is around 10°K.  This hydrogen is in molecular state, H2.  If radiation increases the temperature of the molecular hydrogen, H2, to around 100°K, molecular hydrogen breaks down to neutral hydrogen atom; H2 → H + H. (This state is called HI; H-one).
A cloud, very close to a star, can have a temperature of the order of 10,000K.  At this temperature, hydrogen atoms can ionise and in the process can emit a light of wavelength 656.3nm. (HII state; H-two).  Hydrogen in each state, emit radiation at characteristic wavelength.  Anything above 0K can emit electromagnetic radiation.  Depending on the temperature, the radiation could be from, gamma rays (short wavelength) to radio (long wavelength) range.

How crowded/dusty?
On Earth the density of air is around 1019 molecules/cc, compare this with the typical density of interstellar space, 0.1 atom/cc.  However in the densest region, it can go up to 10,000 (10*103) molecules/cc.  Although in the vastness of space, this amount dust is negligible compared to what we have on Earth, accumulation of dust leads to the formation of stars and galaxies.

Chemical compounds show characteristic wavelength "windows" in the spectrum, that is how we identify the compounds

Can we see it or not / What can we see
If the gas cloud is close to a star, the radiation from the star can heat the gas cloud to tens of thousands of degree; the gas ionises and emits radiation in the visible range.  For example, the Orion nebula, is an emission nebula.
As we have discussed earlier that a dust cloud can scatter light mainly in the visible blue region, for example the Pleiades.  Such nebulae are called reflection nebulae. 
Visible light from the star may get blocked/absorbed by dense interstellar medium and appear as a  dark patch in the nebula, the Horse Head nebula is a good example, a dark area against bright emission area.  Although it is visibly dark, the dust gains can get heated up and radiate in the infrared range, which is invisible to the eye.

How can we look through the dusty layer
We are familiar with infrared cameras, as used in the wildlife filming or (false) colour image of heat loss from a building.  Some infrared astronomy can be done by the terrestrial telescopes (located in dry areas or above the cloud level), using detectors sensitive to infrared range.  Near-Infrared beam is transparent to dust and we can see what lies in the dark areas obscured by dust.  In the image below, blue stars as seen in the visual range is replaced by red giants when seen in infrared.
In the dark globule Bernard 68 in the southern constellation Ophiuchus, the central dark area is obscured in the optical range, but the near infrared image allows to see the background stars. These are not part of the system.  New star formation would occur in the dense cloud.  Spectrum analysis would identify the nature of the cloud.
As we move into longer wavelength, mid to far infrared (5–210µm; (5–210)*103nm), we get images due to the heat radiation from planets, comets and asteroids.  Visual and optical telescopic images of these objects are due to the reflected Sun light.  Cold dust emit infrared and therefore by spectral analysis, we can identify the species.  Like the optical spectroscopy, there are both emission and absorption lines in the spectrum.  These provide information on the formation of planets and stars.
Next, we will look into still longer wavelength, microwave and radio telescopes.

Dark globule Bernard 68 in southern constellation Ophiuchus.  The central dark area is obscured in the optical range, but the near infrared image allows to see the background stars.  These are not part of the system.  New star formation would occur in the dense cloud.  Spectrum analysis would identify the nature of the cloud

Radio and Micro-wave Range
As we move into signals from the still longer wavelength sources, we come to microwave and radio sources.  Karl Jansky was working in Bell laboratory on the cause of the interference in radio telegraphy in the 1930s.  He designed a radio receiver, which might look like a Heath-Robinson set up by today's standard.  He noticed three types of signals, two of these were due to thunderstorms and the third one of these, with a periodicity of 23h 56 seconds, appeared to originate from the centre of the Milky Way.  This time period is important as it is the sidereal time, the time it takes for the Earth to rotate once on its axis.  This indicates that at every 23h 56 seconds the antenna was pointing to the source.  The results were published in 1933 and was the first reported evidence of extra-terrestrial radio source.  Although it was a very interesting result, it did not attract much attention.  There are some reports that Nikola Tesla might have detected a radio signal from an extra-terrestrial source.
Grote Reber, a radio engineer and amateur astronomer, inspired by Jansky's results, using his own resources and time, build a 9.5m parabolic dish, looking like a “conventional” radio telescope of today (like the Jodrell Bank telescope), in Illinois, Wisconsin.  This was a big engineering feet, considering it was an effort by an individual.  Frequency and wavelength are related and the detector in the radio telescope is tuned to receive signals in certain frequency range(s).  Reber did not get any result at higher frequencies, 3300MHz, but got signal at lower frequency of 160MHz.  This was an interesting observation in its own right.  Higher the frequency (shorter the wavelength), higher is the energy of the source, but the signal came from a source with lower frequency.  By the late 1930's and early 1940's Reber published contour maps of radio sources in the sky.  He was a remarkable individual, most of his earlier work was done independently.  Later on moved to Tasmania and continued working on radio astronomy. 
James Stanley Hey, was working with radar for the British army during the war.  There were reports of jamming of radar signals.  He noticed that the direction of the jamming of signal was following the Sun.  At that time the Sun had very active with sun-spots.  Hey concluded that Sun can act as a radio source and interfere with the incoming signal.  George Clark Southworth from the US also reported that the Sun can act as a radio source.  In 1945 Hey noticed short bursts of radar signal, 5–10 per hour from about 96.5km (60 miles) height.  Hey concluded that these are from meteor trails and such trails could be detected both during the day and night.  After the end of the war, spare radars were available and there were people with experience of working with radar, so radio astronomy took off.

Composite infrared image of the centre of our Milky Way galaxy. It spans 600+ light-years across and is helping scientists learn how many massive stars are forming in our galaxy’s centre. New data from SOFIA taken at 25 and 37 microns, shown in blue and green, is combined with data from the Herschel Space Observatory, shown in red (70 microns), and the Spitzer Space Telescope, shown in white (8 microns). SOFIA’s view reveals features that have never been seen before.
Credits: NASA/SOFIA/JPL-Caltech/ESA/Herschel

How are the Radio Signals produced?
Essentially there are three processes
Thermal: Vibration of atoms and electrons, the constituents of (almost everything) of matter, depends on its temperature.  This vibration produces electromagnetic energy.  The higher the temperature, the higher is the frequency, the shorter the wavelength.  A star is hot, it emits electromagnetic waves in the optical rage (shorter wavelength cf. radio range), we can see it in the naked eye or by optical telescope.  But if the temperature is low, vibration does not produce waves in the optical range, but at longer wavelengths.  As an example, a human body of surface area 1m2, with a temperature of say 27°C (300K), produce only 0.01 photons per second at visible light wavelengths, greater than 0.75µm (750nm), but the human body can produce over 1000 photon below 10GHz radio range (3 cm).  Therefore a human body although at a lower temperature, it can emit radio signal. 
Non-thermal: When a charged particle moving in a magnetic field, changes direction, it emits radiation.  If the speed of the particle is slow compared to the speed of light, it is called cyclotron radiation and if the speed of the particle is comparable to the speed of light, as in the case with, black holes, cosmic rays, neutron stars or plasma jets, the radiation is termed as synchrotron radiation.  This radiation is associated with magnetic fields and is polarised in nature. 
Change in the electronic state:  Molecules can rotate (spin) or vibrate only in certain energy levels and if there is any change of energy level, the molecules emit (or absorb) energy in millimetre wavelength levels.  The rotation here does not mean rotation in conventional sense, but it is more like a change of direction within the molecule in atomic scale.  For a hydrogen atom this change in spin is associated with an energy level corresponding to 1420.4MHz, or ~ 21cm wavelength.  This is the oft quoted 21cm hydrogen line.  The spectrum, plot of energy vs. wavelength, shows well defined peaks and therefore is used to identification of species.

Alignment of dust grain along the magnetic field imaged by SOFIA, superimposed on an infrared VLT, Chile, image of Orion nebula.  Magnetic field prevents the collapse of dust grains.

Layout of the telescopes across the globe used in the recent detection of the black hole; Event horizon telescope

A hydrogen molecule is symmetrical, two equal weights of hydrogen atom.  A hydrogen atom is light; atomic mass 1.  A hydrogen molecule, would need about 500K to change the rotational state.  But the typical temperature of the molecular cloud is only around 10K.  Hence the emission from hydrogen is difficult to detect.  But in a molecule like carbon monoxide (CO), there are two atoms of different atomic weights.  This molecule is a lot heavier than hydrogen.  The atomic weight of carbon is 12 and that of oxygen is 16; the molecular weight of CO=12+16.  Such a molecule will emit stronger radiation in millimetre wavelengths.  It has been found that in the interstellar cloud the ratio of a hydrogen molecule to a carbon monoxide one is about 10,000 to 1.  So it is easier to monitor the radiation from carbon monoxide and then extrapolate to hydrogen distribution.  There are a host of other molecules present in the interstellar cloud which emit in the radio frequency range.  By spectral analysis we can identify the compounds present.  Some of these do not form under terrestrial condition. 
The power of the thermal radiation decreases with increases in wavelength, whereas that of the non-thermal radiation, increases with decrease in wavelength.  These two processes produce continuum, or broad band spectrum, i.e. the spectrum covers a wide frequency/wavelength range.
So if we collect spectrum covering a wide wavelength range and plot the energy vs. wavelength, we can distinguish between the thermal and non-thermal source.

Left to right  1/ Combined image of galaxy, stars, dust and spiral arms.  2/ Radio image, cold hydrogen gas blue.  3/ Warm mid-infrared image, dust red.  4/ Stars green

Web Addresses for further information

Two great events of 1990

By Geoffrey Johnstone
The launch of the Hubble Space Telescope and Voyage’s Pale Blue Dot

The first great event of 1990 was the April launch of the Hubble Space Telescope.  Edwin Hubble died in 1953 and it was fitting that the telescope should have been named after him.
What I was not aware of was, a space telescope had been suggested in 1946 by Lyman Spitzer (1914 to 1997), who subsequently had a space telescope named after him.  That telescope operated from 2003 to 2020 and was dedicated to infra red observations.  The Hubble was something else entirely and is still in operation 30 years after its launch.
The story of the flawed mirror is well known and due to a quirk of fate was polished to the wrong figure.  After weeks of testing NASA had to admit a mistake had been made.  I remember Patrick Moore being very scathing about the error during one of his Sky at Night programmes.  He thought any self respecting amateur astronomer could have detected the error in five minutes.  To do so they would have needed the mirror on its edge and there was no facility for standing a 2.4 metre mirror on its edge.  Hubble was launched into quite a high orbit so at first was thought to be inaccessible.  So the first fix was to write some clever software to adjust for the poor figure of the mirror which was producing only blurred images.  They were still much better than Earth based telescopes that had to look through a wobbly atmosphere, but far from what was expected.
The first Shuttle mission to correct the flawed optics took place in 1993 when COSTAR was installed after several gruelling space walks.  To fit it they had to remove another instrument that was thought to be less important.  The result was immediate and spectacular, as it was then possible to obtain images of stars with a resolution 0.05 arc seconds.  The 1993 mission also replaced the wide field and planetary camera which by this time was using out of date technology.  Further servicing missions took place in 1997, 1999 and 2002.  A fourth mission was proposed for 2005, but following the Columbia disaster it was cancelled, as it was thought to be too dangerous.  However when the director of NASA changed the mission was reinstated, and flew in 2009.
Since the Space Shuttle programme was cancelled due to the ages of the fleet there has been no way of any further servicing possibilities.  For the moment and the immediate future Hubble is safe enough and working well, but at some time in the mid 2030’s the orbit will degrade such that it will re-enter and burn up.  As it is a large object some of it is bound to hit the ground.  It may be possible to attach remotely a package that will either boost it to a higher orbit or perform a controlled re-entry over the pacific. 
For the moment long live the Hubble Space Telescope particularly as there are plans for it to work in conjunction with The Webb Space Telescope, should that instrument ever gets launched.  The Webb is vastly more complicated than its predecessors because of which the launch date continues to be put back.  The orbit that the new telescope will be in is inaccessible to any servicing mission so it has to work straight out of the can!

The other great event of 1990

(Other great events include Nelson Mandela released from prision, Margaret Thather resigned, reunification of Germany, Iraq invades Kuwait and Tim Berners-Lee begins World Wide Web)

The second great event of 1990 was the amazing image from Voyage’s imaging team, called the Pale Blue Dot.  This image was taken on the suggestion of Carl Sagan.  I wonder who is old enough to remember Carl Sagan for his popularising of Astronomy and his famous novel Contact.  I particularly remember him from his “lectures to young people” from the Royal Society one Christmas.  Sadly he died in 1996.

The following is from the internet, copyright © The Planetary Society.


Look again at that dot.  That's here.  That's home.  That's us.  On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives.  The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every "superstar," every "supreme leader," every saint and sinner in the history of our species lived there - on a mote of dust suspended in a sunbeam.
The Earth is a very small stage in a vast cosmic arena.  Think of the rivers of blood spilled by all those generals and emperors so that, in glory and triumph, they could become the momentary masters of a fraction of a dot.  Think of the endless cruelties visited by the inhabitants of one corner of this pixel on the scarcely distinguishable inhabitants of some other corner, how frequent their misunderstandings, how eager they are to kill one another, how fervent their hatreds.
Our posturings, our imagined self-importance, the delusion that we have some privileged position in the Universe, are challenged by this point of pale light.  Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity, in all this vastness, there is no hint that help will come from elsewhere to save us from ourselves.
The Earth is the only world known so far to harbour life.  There is nowhere else, at least in the near future, to which our species could migrate.  Visit, yes. Settle, not yet.  Like it or not, for the moment the Earth is where we make our stand.
It has been said that astronomy is a humbling and character-building experience.  There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world.  To me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we've ever known.

Carl Sagan, Pale Blue Dot, 1994
Copyright © 1994 by Carl Sagan
Copyright © 2006 by Democritus Properties, LLC.

This image of Earth is one of 60 frames taken by the Voyager 1 spacecraft on February 14, 1990 from a distance of more than 6 billion kilometres (4 billion miles) and about 32 degrees above the ecliptic plane.  In the image the Earth is a mere point of light, a crescent only 0.12 pixel in size.  Our planet was caught in the centre of one of the scattered light rays resulting from taking the image so close to the Sun.  This image is part of Voyager 1's final photographic assignment.

A Satellite of Venus
By Mark Edwards

As Venus is so prominent in the evening sky I have been taking a lot of photographs of it recently, some more successful than others, but the one that really caught my attention was this one:-

Venus was so very over exposed that it didn't show its true half Venus shape, but below was a curious bright dot.  Checking Venus's position against a star chart showed that there were no bright stars or other planets in that position, so what could it be?  Since when did Venus have a moon?
Well, since 1645 to be exact!  From four observations made between 11th November 1645 and 22 January 1646 a Neapolitan telescope maker, Frencesco Fontana reported that he had seen not one, but two moons orbiting Venus.  In his book, Novae Coelestrium Terrestriumque rerum Observationis published in 1646 he described their appearance: "This is a new discovery not yet published in my opinion, but it is true that they do not always appear, but only when Venus is shimmering.  These little dots were not always seen in the same situation on Venus, but they moved back and forth like fish in the sea."
One of the moons appears in a drawing in the Novea Coelestrium:-

Although some have claimed that Fontana was not a reliable observer, his book suggests otherwise as he accurately described the phases of Venus and Mercury and Jupiter's belts and made the best moon drawings of the time.
All these observations were made with a telescope that was unusual as it used two convex lenses that he claimed to have invented himself in 1608, three years before the generally accepted first one that Kepler had described in 1611.  This claim is written around his portrait in the book:-

The inscription reads: "Franciscus Fontana Neapoli, novi optici tubi astronomici inventor A. Dom MDCVIII Aet. suae 61" (Francesco Fontana inventor of the new astronomical tube in the year 1608 at the age of 61).  There seems to be some confusion as to whether he claimed to have invented the telescope at the age of 61, or 19, depending on which way up the figures are read.  
After Fontana's discovery of Venus's satellites many more astronomers saw these satellites during the 17th and 18th centuries, one of whom was G.D. Cassini, director of the Paris observatory and the discoverer of his famous division in the rings of Saturn.
Cassini wrote in his journal on 28th August 1686: "At 4:15 am while examining Venus with a telescope of 34 feet focal length, I saw at 3/5 of its diameter to the east an ill-defined light, which seemed to imitate the phase of Venus, but its western edge was more flattened.  Its diameter was very nearly 1/4 that of Venus.  I observed it with attention for a quarter of an hour, when on quitting the telescope for five minutes I could not find it again, the dawn being too bright."
Cassini was not the only one who could not find it again, as after 1768 there were no further observations of such satellites of Venus.  This was probably helped by the fact that no moon was seen during the transit of Venus in 1761.
The commonly accepted explanation for the appearance of these illusive satellites was that they were due to reflections within the optics of the telescopes being used, except that two observations made by Peter Roedkiaer at the Copenhagen Observatory on 3rd and 4th March 1764 might have been a pre-discovery of the planet Uranus which was close to Venus at the time.
So if my curious dot was not a satellite of Venus, what was it?  Well, as I suspected it didn't disappear when I took another photograph with the lens cap on the camera, so its true nature was revealed as a hot, or stuck pixel in the camera's sensor.
Looking back at previous photographs it wasn't there when I bought the camera a year ago, so it had obviously failed in the meantime.  Annoyed that I would now have to subtract it from every picture that I took from now on, I did what everyone does these days and googled the problem.  Sure enough I found a YouTube video that claimed an unlikely solution.
My camera is a Canon 200D SLR and the claim was that if you put the camera in manual clean sensor mode that removed the hot pixel.  That seemed unlikely as all cleaning the sensor does is to remove dust by vibrating it.
However, I tried it and it worked!
Eventually I found hidden away in the manual for the camera in the section on activating the sensor cleaning manually, this note:-
"Dots of light may appear on images if the sensor is affected by cosmic rays, etc. By selecting [Clean now], their appearance may be suppressed."
It would appear that stuck pixels are removed by using the average of pixels around them and substituting that value for the missing one So if you take a picture and a star lands on that pixel it will not be registered, but the picture will look normal in other respects.
Doing some more research it would seem that most makes of new SLR cameras include such a feature, so the next time that you have appeared to have discovered a new satellite or supernova you can easily get rid of the annoyance Of course making sure that you have first checked that it is there on a dark frame and not really a new discovery!
Now that I have a clean sensor the question arises as to how can I avoid such damage in the future?  From experiments that people have made it would seem that storing your camera in a lead box makes no difference as 20m of concrete is required to shield it from cosmic rays.  The only thing that can be said is that flying with it in a plane is a bad idea as that removes some of the shielding effect of the atmosphere - not difficult to avoid in these difficult times!

What is a Month?  And other Stories
By Geoffrey Johnstone

January in Roman mythology was Janus.  February was Ferrua the Feast of Purification.  March was named from Mars, the god of war.  April was Aprilis, perhaps from the Greek Aphrodite or a pagan underworld goddess.  May was named after Maia, the Roman goddess of the spring.  June was Juno, queen of the gods.  July commemorated Julius Caesar, born in Rome on July 12 or 13 in 100 BC, and August Augustus Caesar, born in 63 BC and died in 14 AD.  September was from the Latin word for Septem meaning 7.  (now the ninth month).  October stems from the Latin word Octo meaning 8.  (which is now the tenth month), while November was from the word Novem meaning 9. (which is now the eleventh month).  Finally December was from the Latin word Decem meaning 10. (which is now the twelfth month).  Well that’s got that straight then!
A calendar month is a convenient means of dividing a year into twelve and has no other significance, whereas lunar months are concerned with the orbit of the Moon round the Earth.  The orbit of the Moon is not a circle but an ellipse therefore it moves in its orbit at a varying speed.  When at its closest it is said to be at perigee and when at its furthest apogee.  When at perigee it moves slightly faster than it does when at apogee.  The Sun tugs on the Moon so that the point of perigee changes by three degrees each orbit (ie. Perigee precesses in a clockwise direction, making one complete circle of the Earth in 8.85 years).  To complicate matters further the orbit of the Moon is tilted with respect to the Earth’s by 5 degrees.  Taking all this into account means that there are several kinds of month.
If you observe the Moon close to a bright star, 27.32166 days later it will be close to that same bright star.  This period is known as a sidereal month.  The period of time when the Moon returns to exactly the same phase is 28.53059 days and is known as a synodic month.  The period of time from one perigee to the next is 27.55455 days which is 5.5 hours longer than a sidereal month and is known as an anomalistic month.  As the Moon’s orbit is inclined to the Earth’s orbit there are two occasions each month when the Moon passes through the plane of the Earth’s orbit.  One descending and one ascending.  These time are known as the ascending and descending nodes.  The times between consecutive nodal passages is called a nodal month and is 27.21222 days.  These nodes also precess round the Earth, but in an anti-clockwise direction taking 18.61 years to make one rotation.
When three solar system bodies are in a straight line as seen from above they are said to be at syzygy.  The Sun, Earth, Moon or Sun, Moon, Earth for example.  If you can picture syzygy occurring at one of the nodes an eclipse will take place.  About 14 days before or after every solar eclipse a lunar eclipse will be seen from somewhere on the Earth’s surface.
So what is a month?  Sidereal, synodic, anomalistic or nodal.  When we refer to a lunar month we normally refer to a synodic month. (time between consecutive identical phases).  That is 28.5 days.

Smart people the Americans
A friend gave me some copies of The New Scientist and I am having fun trolling through the penultimate page called Feedback, So I thought I would share this item with you.
The US administration is keen to address the impact of climate change on American businesses, principally on the way in which the environmental regulations are impinging on their profit margins.
Thoughtfully US politicians are eager to fill in the looming knowledge gap with their own free spirited theories. National Public Radio reported that Republican senator Scott Wagner told constituents in Pennsylvania “I haven’t been in a class in a long time” – at which any sensible politician would have stopped talking “but the Earth moves closer to the Sun every year, you know, the rotation of the Earth."
Adding to his alarming heliocentric model, Wagner said, “We have more people. You know, humans have warm bodies. So is heat coming off? Things are changing, but I think we are, as a society, doing the best we can.”

You Are Older Than You Imagine
All hydrogen in the universe apart from a tiny amount was created in the Big Bang.  The Human body is made up of 60% water. Therefore as each molecule of water is made up of two atoms of hydrogen and one atom of oxygen, all that hydrogen, plus any other atoms of hydrogen in the body, are 13.7 billion years old.
The first stars lit up between 8 and 11 billion years ago, known as the cosmic noon.  The largest stars rapidly used up their hydrogen fuel, producing the heavier element up to iron. Finally those stars became unstable and blew up as a supernova, in the process producing all the elements heavier than iron.  The products of the explosions enriched the interstellar medium, together with the products of other exploded stars.  From these clouds of material the second generation stars were formed, of which the Sun and its retinue of planets would have been one. 
As the Earth is over 400 thousand million years old, the iron in your blood, the calcium and phosphorus in your bones together with all the other elements that are needed to make you function, are a good deal older that the age of the Earth.  We are all made of star stuff.
Since we have been encouraged to recycle in order to save the Earth, then we should, since we have been recycled, probably many times over.

Get the Girl to Check the Numbers
Sometimes I read an article in a science magazine or Astronomy Now and almost fall asleep reading it.  I may even read the article and at the end can’t even tell you what it was about.  Then sometimes the opposite happens and the subject is so fascinating that I feel energised at the end of it.
A couple of weeks ago I had to take my sister to a hospital appointment and sat outside in the car. I always keep a few old copies of The New Scientist handy for such occasions and read two pieces that were particularly interesting.  One had the title that I have used for this piece of prose.  The article was about the life of Katherine Johnson.  It is very doubtful if you would have heard of her, I certainly hadn’t.  Then in the April copy of Astronomy Now, there were two obituaries.  One was Heather Cooper who was featured in last months MIRA the other was Katherine Johnson who had just passed away at the ripe old age of 102.  If it hadn’t been for the old copy of New Scientist that I had just read, her death would have been of passing interest only.
Katherine Johnson was born in 1918.  She was born as Katherine Coleman on August 26, 1918, in_White Sulphur Springs, West Virginia, to Joylette and Joshua Coleman and was the youngest of four children. _Her mother was a teacher and her father was a lumberman, farmer, and handyman.  She was particularly bright, but black.  She was at high school by the age of 10 and left college at the age of 18 with a degree in Mathematics and French.  This was the USA at its most segregated, Cafes, transport, and work places.  The only work open to people like her was teaching which she did for a while. 
In 1952 she heard that there were jobs on offer at Langley aeronautical lab part of NASA’s predecessor.  Here they were turning out data on jet engines, wing shape designs and all manner of aeronautical problems.  Such employees were human computers, before the electronic version became available.  She was hired in 1953.  There was no stigma to black people at Langley although she was expected to use the blacks own toilet and café.  She refused to use the black ladies room and ate her lunch at her desk.  Johnson’s talent was obvious from the start and within two weeks had won a plumb job in the Flight Research Division, working alongside aeronautical engineers.  Apparently she was confident, amusing to work with and was completely accepted by the other staff. 
When on 4th October 1957 the Soviet Union launched Sputnik into orbit, panic spread through the USA.  After this event Langley became the hub for space research, particularly after President Kennedy’s famous speech. 
The engineers began crash courses on everything to do with space, trajectories, orbital dynamics, propulsion, re-entry and more.  Meetings were held behind closed doors and Katherine Johnson was sidelined.  She kept asking to join the meetings, yet the women computers were thought of as calculators not thinkers.  She also raised questions about their research and so realising that she was a thinker as well as a calculator they let her into the meetings; and so she became part of the space programme. At the same time the USA’s first astronauts moved into the office next door.  At this time she worked with Ted Skopinski and their job was to look at the problem of spacecraft trajectory.  Using dozens of equations they showed how to calculate the location directly beneath a spacecraft at every second of its voyage.  It was a huge task and took nearly two years, yet when they wrote up their results it was a major advance in mission planning.  It enabled astronauts to know exactly when to trigger the retrorockets to re-enter the atmosphere. 
Getting a spacecraft into orbit and back again safely was a big ask and when it was time for John Glenn to make that first risky orbital flight, he fully understood the issues.  By this time a new fangled IBM computer was being used to crunch the numbers and Glenn didn’t entirely trust electronic computers.  To him real computers were people not machines, so he is reportedly said.  “Get the girl to check the numbers,” only then would he fly.  Johnson set to work re working the numbers.  After a day and a half meticulous working through a whole pile of data, she and Glenn breathed a sigh of relief: The numbers checked out.
Johnson watched Glenn’s triumph parade and then went back to work, as backroom personnel usually do.  She went on to achieve much more though.  She calculated the timing for the lunar landings and later worked on the Space Shuttle programme. 
In 2015 her achievements were finally recognised by receiving the Presidential Medal of Freedom from Barack Obama.  A book Hidden Figures: The True Story of Four Black Women and The Space Race. has been published by Margot Lee Shetterly.  This book is about Johnson and some of the other NASA computers.  The book has also inspired a film.

Books by Dava Sobel

Dava Sobel has written several books on astronomy.  I particularly remember the one titled Longitude where she describes the first sea going accurate clock developed by Harrison to determine longitude from anywhere on Earth. The book was made into a dramatised documentary for TV and was screened several times around the time of the millennium. 
Her book The Glass Universe, has bearing on my piece about Katherine Johnson as it describes the female computers and the discoveries that their work lead to.  It describes particularly those ladies that worked for Edward Pickering known colloquially as ‘Pickering’s Harem’.  At the age of only 31 he became director of the Harvard College Observatory.  He was fond of saying that “a magnifying glass will show more that a telescope will show in the sky”.  Pickering was interested in photometry which involved taking glass photographic plates 8 inches by 10 inches and then examining them under suitable magnification.  He gave up using men as computers as they weren’t meticulous enough and anyway women were cheaper to employ.  Equal pay was unknown in those days.  The funds for the research were provided by two widows, Catherine Wolfe Bruce and Anna Palmer Draper.  The Henry Draper Catalogue of stellar spectra is famous in its own right.  Most of the work for this was done by Pickering’s Harem, in particular Williamina Fleming. During her time with Pickering Fleming she discovered over 300 variable stars, and classified more than 10,000 stars using a system that she devised herself.  Another of Pickering’s famous ladies, Annie Jump Cannon, was even allowed to operate the telescope herself.  She developed a system of stellar classification that is still in use today.
In 1912 another famous computer Henrietta Swan Leavitt made one of the most amazing discoveries of all time.  Just by examining these glass plates she found a relationship between the brightness of a particular class of variable stars that varied with the length, or period as it’s more correctly known, of its change in brightness.  This immediately enabled astronomers to find the distance to distant galaxies as long as this class of variable star could be found there.  Leavitt would have received the Nobel prize for this discovery had she not passed away fairly suddenly.  Nobel prizes are not awarded posthumously. 
The Glass Universe is available as a kindle book for £4.99 or £ 18 pounds as a Hardback copy.