Bulletin 09.2 English summary
R. Hooijenga.
Contents of the May 2009 Bulletin, nr. 100
On the occasion of our 100th edition, I have decided
to go the extra mile and compile summaries as material came in. This way, you can enjoy this extra-thick Bulletin even
more without having to wait for the next issue.
Not only that, but now that the ‘ordeal’ of summarizing two issues in such short
succession is over, I plan to make this the rule.
Contents of the May 2009 Bulletin, nr. 100
Summer field trip, 20 June 2009. D. Verschuuren. i
This year’s trip will be quite special, including a visit to the Munster Cathedral with its
astronomical clock and to the old Town Hall, where the Eighty Years' War ended in 1648.
Lunch will be served at Pinkus Muller, near the Cathedral. Then on to Ibbenburen and the
large Ludger / Bloemenbeek monument.
Miscelaneous. Editors. 3
Member Bote Holman knighted.
Download a Word document with extra information on the use of the Astrolabe (see the link provided).
Download this bulletin as a colour PDF file (see the link provided).
Yearly dues are up.
Nicola Severino finds important News about Planetary Hours. F.J. de Vries. 8
(See the original for footnotes)
Dial by Caramvel Lobkowitz with end of 6th planetary hour.
De Vries has been interested for years in planetary hours, and wrote two notes in our Bulletin
as early as 1992.
Over the years, other gnomonists joined in the work.
In 2007, Arnaldi found some interesting literature, prompting De Vries to write a paper in the Bulletin
and a note on the Zonnewijzerkring website.
Until recently, a single figure in the 1925 Drecker book was the only known illustration
planetary hours. That has changed since Severino found three illustrations in ancient
literature.
Antique, temporal, or unequal hours correspond to one twelfth of the daylight period on
any day. Sometimes, planet symbols would be on the dial, and frequently these hours
would be called planetary. However, Drecker, referring to Sacrobosco (1230), defines a
planetary hour as the period in which half a sign of the zodiac, comprising fifteen degrees
of the ecliptic, rises above the horizon. Maurolicus (1575) and Agrippa (1533) also quote
Sacrobosco.
Like temporal hours, there are twelve ecliptical planetary hours during the daylight
period, and twelve during the dark. But unlike temporal hours, which change length over
the year, planetary hours change length over the day. The figures explain using an
astrolabe, and show a complete set of planetary hour lines.
Severino’s first find, in a 1644 book by Lobkowitz, shows a horizontal sundial with one
planetary hour line, for the sixth hour. The other curves are for hours that are multiples
of one ‘ordinary hour’ earlier or later.
His other two discoveries are astrolabe tympanum designs with ecliptic planetary hours,
one of unknown origin from around 1508-1520, the other by Finé, 1553.
Severino also found tables for the beginning of all ecliptical hours by Kretzschmayer,
1626. It is important to note that this author refers to these tables as tabulae horarum
planetariarum, that is, tables of planetary hours.
De Vries concludes that, in addition to hours based on the solar diurnal arc, there
definitely was a planetary hour system based on the ecliptic. He thanks Nicola Severino for
sharing his discoveries.
A closer look at the Prinsenhof Plans. F.W. Maes. 22
Original plan from 1730.
The Prinsenhof dial is one of the best-known and most beautiful sundials. The vertical
dial declines 28 degrees towards west. It is rather hard to read because of all the data it
provides in a single display.
A summary lists: local time (on the perimeter, using the style); Babylonian, Italian, reversed
Italian hours; length of day, sunrise, sunset (using the nodus).
There is a “manual” on the sides of the Gate, and the year 1731.
In 2003, it became clear the Leeuwarden ‘Tresoar’ keeps the original 1730 plans for
this sundial. For just a few Euros, Maes received a scan. The record consists of a single
folded 40x32cm sheet. (The back shows two drawings of a polar dial.)
The drawing header mentions latitude, but not wall declination. The table enables one to
calculate the declination, but that mentioned on the dial itself is half a degree greater.
Fig. 6 shows de difference this would make to the hour lines – not negligible. Is the
drawing correct? Maes projected it onto his calculation for the stated declination; it fits
almost perfectly. He does not know how the the lines were constructed; perhaps the polar
dial drawings have something to do with it.
Unique analemmatic sundial in Culemborg F.W. Maes. 30
This is the first analemmatic in The Netherlands featuring a raised date strip. Without it,
one’s shadow would not reach far enough on a sundial of this size: the major axis of the
hour point ellipse is 7 meters.
Around the hour points is a yellow Hollander circle of 9 meters diameter, which effectively isolates
the design from the northeast-southwest streets.
Stone slabs in the circle indicate the cardinal points.
The axes of the ellipse, likewise in Hollander, extend almost to the circle and end in a block of LED lights.
Suggestive ‘feet’ show where to stand. The sundial indicates civil standard time, not summer time.
Mosaic sundial. F.J. de Vries. 33
A painting of the sky with sun, moon and stars was the basis for an oblong, octagonal,
horizontal sundial in mosaic. Borsje converted the idea into a working plan.
Link for some more details.
Astro Clock (part 2). B.P.U. Holman. 34
This instalment describes the construction and operation of the clock. An important
feature is that on its dial, the sun remains in each sign of the zodiac for as many days
(from 29 to 32) as in reality. This makes it possible to include a calendar in the display,
which shows the values of as many as ten variables, including the equation of time.
B2008.3, Equation of Time calculation postscript. F.H. Fockens. 42
The original paper disregarded the influence of moon and planets. More importantly, the
calculation was not yet quite precise. Jean Meeus provided a modification.
– Finally, a correction to equation 11 is repeated here.
Largest vertical sundial in Brussels, Belgium. W. Leenders. 48
This remarkable concave cylinder sundial was built in 2005, on the front of a new
building. The dial face, on the middle part of the front, is 6,5m wide and 3,3m tall; it occupies
the fifth and sixth floors.
De Graeve made the first design and supplied geographical data; Leenders calculated the pattern.
Both are committee members of the Flemish Sundial Society.
While a cylinder sundial is relatively common (think of the shepherd’s dial), a dial on the
inside of the cylinder surface is quite rare. Leenders’ calculations were cross-checked
using a different method by De Vries, and later compared with one by Savoie for a full
cylinder (cf. Hollander’s Sundial Glass).
The hour line pattern is adjusted for longitude and daylight saving time (together
1h43m), so that in summer the dial reads civil time, except for the equation of time,
which in summer hardly matters.
There are three date lines for the seasons.
The customer made the nodus ball rather larger than designed. Its shadow is now 35 minutes
wide, and judging the centre is less precise than necessary.
The concave surface results in a relatively compact dial. A flat dial using the same nodus
distance would have been 45 times as big.
Since recently, there is a comparable sundial in New Haven, CT, built with the help of
F.W. Sawyer. This is a direct south, half cylinder; the Brussels sundial is a quarter
declining towards SSW. And the nodus did get its optimum size, in contrast to the
Belgian one.
Almost cylindrical is the 1987 Disney sundial in Buena Vista, FL by Isozaki. Its gnomon is extended
to outside, and has a corresponding pattern on the outside of the building as well as on the inside.
Calculation of a sundial on a concave cylindrical surface. W. Leenders. 50
The algorithm described outputs shadow coordinates for date and time fed into it.
Phase one calculates coordinates on the vertical plane behind the cylinder using wellknown
equations.
Phase two projects these onto the cylinder surface.
Finally, in phase three, the cylinder is unrolled, producing measurements along its surface.
A century of synchronized clocks. NRC. 54
Until 1909, each city or region in The Netherlands kept local time: that of the sundial that
was used to set the church clock.
On 1 May 1909, all clocks were set to Amsterdam time, which was GMT plus 19 minutes
and 32.14 seconds, corresponding to the longitude of the Westertoren.
Holland was a participant in the Washington International Meridian Conference of 1884, but apparently
could not decide whether to adopt the time of the London time zone, or that of the Berlin
time zone. It was not until the German occupation in 1940 that Central European Time
was introduced.
Kite sundial. J.A.F. de Rijk. 56
This sundial, cut out of an A4 sheet of thick stock and folded into shape, is well suited to
illustrate the relation between horizontal and vertical dials. It may be good to brace the
construction with a strip of cardboard against the vertical back.
Incorrectly set up pole style sundials. H.J. Hollander. 58
One frequently finds sundials that are not aligned well – or at all. Hollander presents an
elegant method to determine the resulting errors over the day and year. To this end, he
uses a “spider” dial, which is a round dial with a perpendicular gnomon. Normally, the
gnomon is vertical, and one reads time at the intersection of the gnomon shadow with
the actual date circle. In this case, and on our latitude, the hour lines are quite wavy and
reminiscent of the legs of a spider.
When one aligns the spider dial gnomon in parallel with a correctly set up pole style, the corresponding
hour line pattern is that of an equatorial sundial. It is marked on the dial
face. With the gnomon subsequently aligned in parallel to that of the erroneously placed
sundial, the hour line pattern on the spider dial disk is, naturally, different.
It is now a simple matter to read the difference for any desired date and time by
comparing the two patterns.
Figure 2 shows the errors in a dial for 52 degrees latitude used on 22 degrees, but still
aimed north. Figure 4 is for a dial for 12 degrees west declination, used with 50 degrees
east declination. This is the actual situation for the sundial in the figure 3.
Annual meeting, Utrecht 21 March 2009. Secretariat. 60
- Twenty-four members were present.
– The Zonnewijzerkring will be present on the large NEMO (Amsterdam) exhibition on IYA2009.
New handouts were printed and flags made.
– Appingendam Museum asked for sundials on loan for an exhibition on Time.
– De Rijk has added the NWO (Netherlands Organisation for Scientific Research) prize to his
trophy-cabinet. He will use the €12k5 prize money to have a Huygens telescope built (a
30m affair without tube), as well as a sun simulator for testing table top sundials.
Vincent Icke is involved in the telescope venture; members Sasbrink, Vesters and Pals volunteer
to help with the GHL sun simulator.
– Holman proposes to have the summer field trip in Munster, Germany and to visit the astronomical clock and various sundials.
– The Society may subsidize sundial projects in certain circumstances.
– Chairman De Groot resigns according to schedule, and is re-elected.
- Holman shows a presentation on his project “Art in Signs (of the Zodiac)” and his Italian
prize, and one on his Astro Clock.
– Maes has, through Mrs. Witte, some (pocket) sundials for sale.
- In Culemborg, he helped build an analemmatic sundial with a raised date strip.
- For the restoration of the Echten dials he is raising money.
- Maes is also guiding the correction of the Arnhem folk museum analemmatic.
- Finally, a Belgian sundial is very much like Maes’ design of the multiple-polar style dial.
– De Vries is, with Severino, involved in investigations into the origin of Planetary Hours on sundials. Fer’s calculations and interpretations add much to the understanding of old text and graphics. See elsewhere in this Bulletin.
– A number of sundials by v.d. Belt are on display in the Eindhoven Public Observatory.
– Sasbrink mentions the Restoration Fair in Den Bosch.
- At the conclusion of the meeting, chairman De Groot presents a bottle of Sundial Wine to
Holman, for winning the Italian competition, and one to De Vries, for his contribution to
knowledge about sundial history and the use of planetary hours.
Notes, 2008 statistics and 2009 estimates. Treasurer. 64
The society celebrated its 30th birthday in 2008. Members received a sundial glass and a
book listing all accessible sundials in the society’s database.
Printing costs have gone up slightly [mainly because of thicker Bulletins!].
The Zonnewijzerkring Policy Plan. Treasurer. 66
A formal description of what the Society is and does. The four statutory goals are
explained in more detail.
Literature. Vd Hoeven, Maes, Verschuuren. 68
Contents of Bulletin 99, January 2009. R. Hooijenga. 77