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Transit instrument. (The fundamental apparatus of any self-respecting observatory.)
See NORTHERN SKIES: The Auroral Observatory based on Rousay, Orkney.
John Vetterlein became a member of the British Astronomical Association in 1951. Having little money at the time (he was still attending school) he joined the Computing Section of the Association, to which he has continued to make contributions up to 2012. He has also contributed to the Mercury & Venus, Auroral, Minor Planets, Comet, Solar and Lunar Sections over the years. He was the BAA's area representative for the Campaign for Dark Skies up to the time of his resignation in July 2013. He is a former Fellow of the Royal Astronomical Society (1957 to 1972 - Honorary Auditor 1960/61).
A Personal Cosmology
I recall an occasion, many years ago now, when a number of us were sitting in a Lyons Corner House having just attended a meeting of the British Astronomical Association. A well publicized amateur astronomer of the time had written a book which had been scathingly reviewed by a professional. One of us had a copy of the book from which he read extracts, much to our collective amusement. We too were rather cruel, I think. The author of the book had promised to explain—in layman’s terms—all about Special Relativity; but when it had come to the chapter where all was to be revealed, we were told that the subject was “beyond the scope of the present book.” This, at least, was honest—if belatedly so.
The claims I make for my own booklet are summed up in the title. We all have a right to a little bit of cosmology. This is my contribution, based on some sixty years thinking about things.
There are more things in heaven and earth, Horatio,
William Shakespeare: Hamlet, Act I Scene V
Infinity - the chicken and the egg.
All those stars we say are out there,
(The author: Cobbett’s Field)
Assigning an age to the “Universe” (in years or any unit one cares to choose) falls into the same category of folly as Geocentric Theory once did. It is no more than a Homo Sapiens centred illusion tied to the apron strings of “Big Bang”, a time-based aberration of thought as distinct from a purely spatial one.
Maximum Elongations for Mercury & Venus
Venus reaches maximum elongation (E) from the Sun on August 20 2010.
There is a curious sentence appearing in the later editions of General Astronomy by Sir Harold Spencer Jones (it does not occur in the first edition of 1922). From Chapter X, second paragraph under Mercury, we have: The stellar magnitude of Mercury at greatest elongation varies between -1.2 and +1.1, according to distance.
This loose statement (uncharacteristic of the meticulous former Astronomer Royal) struck me immediately. It is quite clearly factually wrong since even within the wide range of Mercury’s elongations such extremes in magnitude could not be reached. It prompted me to compare the characteristics of phase and magnitude for the two inferior planets at their maximum elongations from the Sun.
Examining the data for Mercury from May 2010 to July 2013 (21 elongations) we see that Mercury has a magnitude of +0.6 on June 12, 2013 (phase 38.3%, elongation 24.3˚) and on February 16 of the same year, a magnitude of -0.5 (phase 52%, elongation 18.1˚).
Not surprisingly Venus, with its highly symmetrical orbit, demonstrates very little variation between maximum elongations, thus: phase 48.4% mag. -4.3 and at phase 51% mag. -4.4. The extremes in elongation values themselves are likewise consistent, falling between 45.4˚ and 47.1˚ approximately.
The other notable difference between the two planets is that maximum brilliance occurs for Mercury close to superior conjunction (mag. -2.3 in the most favourable circumstances) whereas for Venus maximum brilliance (-4.7) occurs when the phase is around 25% to 27%. Theoretically both planets when centrally transiting the Sun’s disc will reflect no sunlight towards Earth at all (Venus with its atmosphere will scatter some light earthwards) and so may be considered to be black bodies with an infinitely high stellar magnitude.
Some of this poses a little difficulty to compilers of internet information on Mercury where ranges in magnitude for the planet are variously quoted as anything between +5.0 and something approaching -2. Wikipedia, at my suggestion, have adopted a maximum brilliance for Mercury indicated by a visual magnitude of -2.3. The other end of the scale is more problematical!
I have written extensively over the past fifty years concerning the visibility of Mercury. I give a more recent reference from the Journal of the British Astronomical Association: http://adsabs.harvard.edu/full/2006JBAA..116..271V
Ideally, for a good daylight view, the planet should be high in the sky and at a reasonable apparent angular separation (elongation) from the Sun. As noted in the above letter, it is possible with small apertures with the object glass suitably screened from direct sunlight, to see Mercury close to the Sun’s limb. However this should only be attempted by experienced observers and preferably with the planet east of the Sun so that in the case of drive failure the Sun itself is NOT brought into the field of view.
Here is a recent image obtained using a Minolta Dimage F200 digital camera taken through the eyepiece of a 120mm f/7.5 apochromatic refractor (see below). Seen with the eye the image was at times a good deal clearer than this.
Today it is possible, using dedicated CCD equipment, to secure images of Mercury (in daylight) that would have been thought unattainable fifty years back. The reader should search the web for examples of Mercury imaging.
I do not have such equipment since I would find it difficult to use a laptop or other computer “wired up” to the telescope. Most of my work on the aurora, minor planets and comets, may be covered using digital cameras harnessed to telescopes or suitable lenses attached to the camera—wide angle and long-focus telephoto lenses, for example.
Iridium fleet of artificial Earth Satellites to be upgraded.
So, our skies are to be invaded by even more of these flashing objects. Astronomers are well aware of the problems these things pose for both visual and photographic observations of the night sky.
To have a near point source of light flash at you through the telescope with the brightness of a full moon can impair vision for minutes.
It is now almost impossible to image parts of the night sky without picking up a satellite or two. When engaged on a project for asteroid No. 433 Eros a few years ago, nine out of ten frames were streaked with satellite trails. In one frame there were no fewer than five trails!
This may be fun for some, but for the serious student of astronomy all this clobber is a curse. And all for what? To give folk down here the means of communication from sauna to mountain top, from one end of a school bus to the other!
2010 June 02
The standard instrument for positional, photographic work in professional observatories comprised two refractors of equal focal length, one for guiding the other acting as the "camera".
These would be long focus instruments in order to provide large scale photograph from which the positions of stars, minor planets etc. could be determined to a high order of accuracy (1/100 arc-second).
The principle is emulated in this small version where 100mm and 120mm apochromatic refractors of identical focal lengths (900mm) have been mounted in parallel on an EQ6 equatorial mount.
The larger aperture instrument (f/7.5) is used with a digital camera attached at the prime focus (not shown) with drive corrections being made on the 100mm scope using an illuminated filar micrometer (not shown).
Today there are autoguide systems that make manual guidimg unnecessary. Everything has been reduced to armchair stuff where the observer may sit in the comfort of a consul without any need to know where to look in the sky for the object under investigation.
This "at distance" approach may have its merits but it is hardly the way to get to know the night sky, just as a satnav device will not give you much idea of how you get to your destination, always assuming you get there!