MIRA 30

June 1993



HIPPARCHUS


CRATER . . . . . . . . HIPPARCHUS
LOCATION  . . . . . 6°S  5°E
DATE  . . . . . . . . . 1993 / 4 / 28
TIME  . . . . . . . . . 20.35 UT to 21.25 UT
MOON  . . . . . . . . 6 days old
LUNATION . . . . . 870
COLONG . . . . . . . 357
SEL. LIBRATION  -5.9 long.  4.9 lat.
OBSERVER . . . . . IL Clarke, Warwickshire.
CONDITIONS . . . Clear, strong wind, seeing 3/5
INSTRUMENT . . . 102mm Refractor, 10mm Plossl +1.8 Barlow = x180

This large ancient enclosure, HIPPARCHUS (138km in diameter), is in a sad state of repair, with very broken walls, it lies near to the centre of the visible side of the moon.  It has been worn down by the impact of numerous meteorites and the passing of aeons of time, until today it is only visible briefly, as the terminator passes by, at very low angles of illumination.  Within a day or two, as the sun rises and the sun angle changes, it soon becomes faint and indistinct.  The crater in the south wall is HALLEY (36km) with all of its floor in deep shadow.  HORROCKS (29km) is embedded in the south east wall.  Just away from the east side of Horrocks was the crater PICKERING (15km), this looked to be a new fresh crater in this area of old structures.  A sharp valley cut through the eastern wall of Hipparchus, Rukl's Atlas of the Moon shows two of these valleys close together.  The floor has been flooded by lava possibly from the Sinus Medii through breaches in the northern wall linking it.  Across the western floor of the crater were numerous markings, some looking like buried or flooded craters, all of these marking had the appearance of very shallow features indeed, requiring a sun only a few degrees above the horizon to be visible at all.  The central crater cast a long shadow over the floor from its western rim, while to the south ran a short rille like mark.  In the western dark shadow area two bright peaks shone brightly.  Hipparchus was a early 2nd century BC Greek astronomer who made one of the first star maps.



A Historical Note
by Vaughan Cooper

During the early 1940s, the Journal of the British Astronomical Association devoted a few columns to letters sent in by members under the title of 'Astronomical Queries', while the Editor would endeavour to obtain authoritative answers.  The following extract is submitted purely for passing historical interest only, as it was a query sent in by one of our own members (who apparently wished to remain anonymous) and published in the JBAA, March 1942 Vol.52 No.2. Which incidental in those days was priced at 3/-, 15p for younger members. The extract reads as follows along with the reply: "A member of the Astronomical Society of the Technical College, Coventry while observing Saturn on 1941 October 28th. at 20h. 20m., discovered a luminous patch which extended in length and varied in brightness.  The phenomenon lasted about 15 minutes.  Did any others observe this?  What is the explanation?  Answer- Eliminating the possibility of the phenomenon being due to aircraft, the only other explanation is that it was the trail of a fireball.  Such a trail could persist more than 15 minutes, and in many cases these trails have lasted for much longer than this.


Perhaps the fireball, if such it was, was observed by others.  If so, details should be sent to the Editor -
M. Davidson





BAA campaign for Dark Skies

The leaflet reproduced below is from the British Astronomical Association outlining their plan for cutting light pollution.  This is now a serious problem for some of the worlds major observatories, especially in America.  All of us who look at the sky will know how much the stars have seemed to dim in just a few short years, not just because we're getting older, but being hidden behind a creeping orange glow from every road, town and city. This sky glow is light which is being wasted and this is energy we are paying for.  Most of this is caused by bad design and poor fitting of lamps which direct the light in a haphazard way to where its needed.  Most of it in some cases, lighting up the undersides of passing aircraft!  Of cause some light will get up into the sky no matter how good the lamps are by reflection off the ground.  But this would be a small amount compared to the amount now being wasted.  If you would like to obtain further information, just write to the BAA. 


baa light pollution






How to follow a short-period variable star
By Tristram Brelstaff


1/  Draw or copy this blank graph on to a sheet of paper and keep it in a safe place.

2/  On every clear night when Lyra is well above the horizon use the comparison stars shown in the following chart to estimate the magnitude of Beta Lyrae.  For each observation record the following details in your note book:



The Date;
The Time (use GMAT = UT -12h = BST -13h);
The Estimated Magnitude (to the nearest tenth);

3/  At the end of each nights observing, calculate the JD (Julian Date) of your observation.  First look up the JD for day zero of the month using the table below.  Add to this the day of the month to give you the JD for 0h GMAT of that day.  Then convert the time (GMAT remember) to decimal parts of a day and add that on to give the JD of your observation.  As an example, 1988 August 26th 11h  55m GMAT becomes
JD2447374+26+(11+55/60)/24 = JD2447400.497



4/  Now compute the phase of your observation relative to a particular zero-point JD and to the period of the star.  It is convenient to take JD 2440000 as the zero-point JD and the period of Beta Lyrae is 12.937 days.  The phase is found by

  Phase = Frac  / JD-ZeropointJD \
                      \———————— /
                       \      Period      /


The Frac (Fractional part) of a number is the difference between it and the largest whole number that is less than or equal to it.  So, for instance, Frac(1.7) = 1.7 - 1.0 = 0.7 but

Frac(-1.7) = -1.7 - (-2.0) = 0.3.   The phase of the above date would therefore be


Frac / 2447400.497-2440000 \ =Frac(572.04)
                                  \ ————————————/
                                   \           12.937           /            = 0.04

5/  Plot your observations at the appropriate place on the graph.  If the phase is less than 0.5 then you can also plot another point at the same magnitude but one cycle later on the phase coordinate.   Thus an observation at phase 0.04 could also be plotted at phase 1.04.  You will need to make 30 or 40 observations to form a decent light-curve.


This shows a part of a record sheet of observations taken of the star BETA LYR.  The data can now be put into a graph to form part of the light curve.





Poets' corner

'The Stargazer's Anthem (with apologies to Rudyard Kipling)

If you can watch the skies while all about you,
Folks laugh, and shake their heads, and smirk with glee;
And tap their temples knowingly, and doubt you,
And look at you as they have looked at me...


If you can stay outside, and not mind being
Frozen stiff, and chilled right to the bone;
And not be daunted by haze or bad seeing,
And never curse or grumble, swear or moan...

If you can smile, and not fly into rages,
When clouds appear from sunset's dying glow;
And the one clear night you get in simply ages
Coincides with moonrise - don't you know...

If you can stay on course without complaining.
When all the heav'ns seem so clear and bright-
Then rush outside, to realize it's raining,
So there's no more observing for tonight…

If you can do the things that I have told you,
And still appear to be both calm and sane-
The Universe's beauty shall enfold you,
And a starry night shall be yours once again.

So let them laugh - it's still the same old story,
And forgive them of their mockery and mirth;
And remember that a night of star-filled glory
Means more than all the treasures of the Earth.

So listen to the things that I advise you,
And persevere until the very end;
And then you'll find (and it may well surprise you!)
That you are an astronomer, my friend!

Julie Peck
St Helier, Jersey
July 1991 / Popular Astronomy






Bode's Law and The Celestial Police
by Mike Frost


I'll start with Bode's Law, which isn't a law and wasn't discovered by Bode.

It was an interesting curiosity first pointed out by Johann Daniel Titius in 1766. We'll come to Bode later.  Titius took the arithmetic "sequence" 0,3,6,12,24,48,96..., where each number is double the previous, added 4 to give, 7,10,16,28,52,100... and finally divided by 10 to give the following table:


Planet                Distance from sun in                           Bode's Law
                       Astronomical Units (AU)                     Prediction in AU

Mercury                    0.39                                                 0.4
Venus                       0.72                                                 0.7
Earth                        1.0                                                  1.0
Mars                         1.52                                                1.6
Jupiter                      5.20                                                 2.8
Saturn                      9.54                                                10.0

The predictions are in remarkable agreement with actual planetary distances. However, there are two problems with this table - first, the original sequence is not a proper geometric sequence, the 0 at the front doesn't fit.  Extrapolating the sequence back gives 1.5,3,6,12,24... which would give a distance for Mercury of 0.55 AU - a long way out.  Second there was a gap in the table in between Mars and Jupiter.  No planet was observed at 2.8 AU from the sun.

For these reasons Titius' table went largely unnoticed, until 1781, when William Herschel discovered a new planet, Uranus.  When the orbit of "the Georgian Planet", as it was originally called, was computed, it was found to lie at 19.2 astronomical units from the sun, in excellent agreement with the next number in the table, 19.6.  The person who pointed this out was of course Bode.  At first he did so without crediting Titius, and so the "law" came to have his name attached.  Personally, I have my suspicions that the real reason the law is named after Bode is because everyone knows where to put the apostrophe in Bode's law, but Titius'/Titius's law is altogether more controversial!
"Law" was altogether too strong a name for the sequence - not only was it still doubly flawed, but there was no hint of any deeper theory behind the numbers.  Nevertheless, the extra entry for Uranus convinced many that there might be something to Titius' table, and attention turned to the gap between Mars and Jupiter.  Was there a planet there waiting to be discovered?
In September 1800, a group of mainly german astronomers met in Lilienthal, and decided to search the skies, to try and find the missing planet.  They were nicknamed the "Celestial Police", and were led by Johann Schroter, who you may know better for his work on the solar photosphere.  Then there was Wilhelm Olbers, of the paradox fame.  The secretary of the Police was Baron Franz Xaver von Zach, a Hungarian aristocrat.  The Celestial Police set to work systematically to observe the ecliptic, the region of the sky in which all the planets move (any planet not moving in the ecliptic at 2.8AU would be quickly pulled into line by the gravitational attraction of Jupiter).
The textbook writers seem to take a strange delight in recounting that the search was then won by an outsider!  On January 1st 1801, Giuseppe Piazzi of the Palermo observatory in Sicily was compiling his own catalogue, when he came across a 6th magnitude star not on it!  He tracked it over a period of a few days, then fell ill and lost it, but had enough observations to be able to announce the discovery of a new planet, somewhere in the Bode gap! He named it Ceres, after the greek god of agriculture (and Sicily).  The world Ceres is pronounced just like the baseball championship.
It might seem unlucky on the Celestial Police, to have their prize discovery made elsewhere by accident, and then lost again before they could confirm it!  However this is very unfair on Piazzi, who must have been a very dedicated observer to be at work on the first night of the new century, when I suspect that most of the rest of Europe was suffering a hangover!  Anyway, there was no animosity between Piazzi and the german astronomers, indeed in later years Piazzi joined the Celestial Police.
The Celestial Police may have been peeved to be beaten to their goal by a stranger, but there was still a difficult task before them - the recovery of the new planet from the few observations made of it, over a tiny span of its orbit.  In this endeavour they had a formidable ally, the brilliant mathematician Karl Friedrich Gauss, who was just beginning his career.  Gauss took the computation of Ceres' orbit (another apostrophic nightmare!) as a challenge to his intellect, and as so often in his life, his solution to the problem, the "least squares" method of curve fitting, was to prove enormously useful by itself (other famous Gauss discoveries were the bell shaped "normal curve" in statistics, the first proof of the fundamental theorem of arithmetic, "every polynomial equation has a solution", and much work in the infant theory of electrostatics).
Anyway, Gauss produced a prediction of Ceres' orbit, and on Dec 31st 1801, forsaking his own new year's celebrations, Olbers relocated the planet, only half a degree from where Gauss had said - at last a success for the Celestials! Olbers was not content with this, and over the next ten years he discovered two more planets in the Bode gap, namely Pallas and Juno.  Harding, an assistant of Schroter, discovered a fourth. Vesta. All were rather smaller than Ceres.  Ceres itself wasn't exactly huge, only 600 miles in diameter.  Inevitably, speculation continued that the four new planets, or asteroids as we now know them, were the remains of something larger.  Had there once been a full sized planet in the Bode gap. which was shattered to pieces in some catastrophe?  It was a beguiling theory, and one which has had its proponents, serious or pseudo, ever since.  Although interest in the Bode gap decreased after the first four asteroid discoveries (the Celestial Police disbanded in 1815), searches continued, and in 1845 a fifth asteroid, Astraea, was found, the first of a steady stream.  Currently over 4000 have been located, mostly photographically. There are many interesting features to their distribution - mostly the result of Jupiter's influence - resonance gaps swept clean by Jovian gravity, the Trojan asteroids pinned in the Lagrangian nodes of Jupiter's orbit, and the "Earth grazers" knocked out of regular orbit by Jupiter and Mars, in towards the inner solar system.  However, the estimated total mass of all asteroids, discovered and yet to be discovered, still falls well short of planetary size.  It seems likely that the asteroids are detritus left over from the formation of the solar system, rather than a planetary cataclysm.
So what of Titius' table?  The asteroids were only a partial success, but Neptune was a disaster.  At 30.1 AU it is nowhere near the predicted value of 38.8 AU (Pluto, curiously, comes in at a mean value of 39.4 AU).  These days the Bode-Titius law is regarded solely as a historical curiosity.
And the Celestial Police?  Well, in 1923 the astronomical community held its "medal-ceremony" for the pioneers of asteroid discovery.  The thousandth asteroid to be discovered was called Piazzia, in silver medal place the 1001st was named Gaussia, and the bronze medal and the 1002nd asteroid went to Olberia. Bode, the "Eddie-the-Eagle" of asteroid hunting, wasn't even in the running!



SCHILLER


CRATER . . . . . . . SCHILLER
LOCATION . . . . . 52°S  39°W
DATE . . . . . . . . . 1992 / 1 / 16
TIME . . . . . . . . . 19.00 UT to 20.00 UT
MOON . . . . . . . . 12 days old
LUNATION . . . . . 854
COLONG . . . . . . 53
SEL. LIBRATION  -5.7 long. -3.1 lat.
OBSERVER . . . .  IL Clarke, Warwickshire.
CONDITIONS . . . Good, seeing 3/5      
INSTRUMENT . . . 102mm Refractor 10mm & 7.4mm Plossl +1.8 Barlow = x135, x180, x243

SCHILLER is a strange looking crater, at first glance it looks like it is the result of two craters joined together, it's 181km (113 miles) long by only 77km (48 miles) wide and because it's at 52° south and lies across the line of sight, this makes it looks even thinner.  It's floor is 3800m deep, very smooth and flat with only a small hilly area at the NW end.  This area looks like a collection of low hills or craterlets which was mostly covered by shadow.  I could see only one small crater on the floor near the west wall where the feature widens.  Why Schiller is the shape it is, is a mystery.  Some think it is a fusion of two craters, but there is no evidence of any continuation of the wall between the two half's.  The eastern wall contained a few small craters and a large shadow area covered the floor at the south end.  The east wall cast a fairly smooth shadow onto the floor of Schiller indicating few hills.  The south wall blended into the surrounding area at the top of the crater wall with a gap or valley linking to a crater at the end of the main axes of this feature.  The western wall looked to be made of a series of low dome hills casting shadows on to the mare.  A shallow crater was prominent on top of the wall at the NW end.  On the sunlit walls could be seen a step like terrace, with horizontal lines of shading, but this was very faint and not at all easy to see.  A faint darker area at the bottom of the west wall was possible a rough area of fallen rock.



EYE on the SKY

Summer, well the rains got warmer and the nights have got shorter, so it must be.  This is the time of the year that most amateurs forget all about the night sky.  Living as we do at this latitude gives us long sunny evenings without any really dark skys for well over a month each side of the 21st of June.  Astronomical dark is when the sun lies more than 18° below the horizon, and this does not happen at 52° North for about 70 days of the year.  Even the moon is hard to find being low down in the sky as it follows the ecliptic.  The sky is just a very dark blue, with maybe two or three of the brightest stars showing.  So if you are out around midnight, you'll find there is a soft glow of light from the north which hides all those deep sky objects you read about in the American astronomy mags.  Their stars shine bright because most of the states lie at far lower latitudes than us. Hence dark skies. So nothing to observe.  So we all pack our scopes away. All, that is, apart from the ones who are into solar observing.  I must admit that I have never had a real go at this part of our hobby as I'm only too well aware of the dangers of pointing a pair of binoculars or a telescope towards the sun.  Even the finder scope on the side of the main tube has burnt and singed a few folk who forgot to cover its front!

The best (and safest) way to look at the sun, is to project its image on to a sheet of white card a foot or two behind the eyepiece after fitting a sun-screen made from sheet of stiff card around the telescope or binoculars to create a shadow patch covering the area where the image will fall.  The image of the sun is focused onto this surface and any spots will show up easily.
A drawing can then be made of any spots visible.  I am always surprised at how faint this projected image can be and it needs careful study to spot the smaller spots.  A quick check by projecting the image with one half of a pair of binoculars will show whether the sun has any markings that day.  The sun has now passed the peak of this sunspot cycle but so far has not had many days with a clear unblemished face.  So do have a go at this branch of astronomy and send in your results for the other members to enjoy.

(IC Ed)