~~NOTOC~~ ===== The 6" Merz refractor ===== ==== History ==== * Purchased in 1838 by [[history:Kaiser]]. * Manufactured by George Merz in the Optical-Mechanical institute of Fraunhofer, Utzschneider and Reichenbach. * It used to be on top of the academy building. * It was used to observe (small) planets, comets and binaries. * The original wooden base was replaced by a metal one in the 1930s. {{ :telescopes:kaiser-opstelling_oude_sterrewacht.jpg?200|}} {{ :telescopes:6_duims_1908_zw.jpg?200|}}On the southern side of the roof of the Old Observatory you can find the smaller of the two prominent domes which was build in 1860 and rebuild in 1874/1875 as well as in 1932. It houses the oldest telescope we have at the Observatory, the 6 inch Merz-refractor which is even older than the Observatory itself. When [[history:Kaiser]] became director of the Observatory in 1837, the instruments at the observatory were in very poor condition. Kaiser closely followed the German astronomer [[wp>Friedrich_Georg_Wilhelm_von_Struve|von Struve]], who had just ordered a telescope from Merz. Ultimately Von Struve decided not to buy the telescope and Kaiser took his chance and bought it in 1838. It was manufactured in the Optical-Mechanical Institute of Fraunhofer, Utzschneider and Reichenbach in Munich by George Merz (1793-1867). The back then Imperial Russion Observatory in Tartu (Dorpat) has a telescope that looks very similar to our original 6". Some people believe that the telescope was manufactured by [[wp>Joseph_von_Fraunhofer|Fraunhofer]] himself. This cannot be true because he died in 1826. As said before, it was build by the firm G. Merz & Mahler. However, Fraunhofer certainly started the manufacturing of the optics. His name can be read near the eyepiece (({{:telescopes:6_duims_eyepiece_holder.jpg?300|}})). Fraunhofer was a partner in the firm Utzschneider & Fraunhofer. Utzschneider was the businessman, the others gifted scientific technicians. Merz was a student of Fraunhofer and he took over this firm from Utzschneider in 1838. ((sources [[wp>Joseph_von_Fraunhofer|1]],[[http://www.werkgroepleidsesterrewacht.nl/page.php?7|2]], en [[http://www.plicht.de/chris/35fraunh.htm|3]])) It was put on the roof of the Academy Building, which still functioned as the Leiden Observatory at the time. The telescope arrived at the observatory the 18th of October at 9 o'clock in the morning, packed in five crates. It survived the journey with only minor damage to the declination circle and was installed in the academy building by 1 in the afternoon. The only problem was that Merz did not provide a micrometer for the telescope, rendering it useless according to Kaiser. However, he ordered one from Merz telling them to deliver it with haste. However, like he said in his book even Kaiser had to admit that a respectable company like Merz would not postpone anything without good reason.(({{:books:het_observatorium_te_leiden.pdf|Het observatorium te Leiden}} pp 103)) At the same firm, Kaiser ordered a very precise clock, but unfortunately this clock was so sensitive, that it was disturbed by the big clock tower that stood next to the observing platform on the Academy building. (The platform is gone, but the clock is still there). Kaiser mainly used his telescope to observe (small) planets and comets to predict their orbits and to observe binairies. The main reasons he bought this telescope was its parallactic or [[wp>Equatorial_mount|German equatorial mount]] and its clock driving mechanism because of which objects could be followed automatically during observations. The original mount was made of pine wood with a mahogany shell(( {{:telescopes:6_duims_tartu_fraunhofer_mount_1833.jpg?200|}})) ((Iets over de korteling voltooide groote kijkers uit München, voor het Keizerlijk Observatorium, op den Pulkova, bij St. Petersburg, door F. Kaiser te Leiden, (Alg. Konst- en Letterbode No. 30 en 31, van het Jaar 1839). pag. (8-9): [...] Het verdient eene bijzondere melding, dat ook de buis des grootsten kijkers uit hout is zamengesteld. [...] de houten buizen uit München bezitten, behalve grootere ligtheid, eene ongeloofelijke standvastigheid. Zoo heb, in de koudst van den winter, het voorwerpglas van de kijker te Leiden, [...] nog geene de minste afwijking bespeuren. Te München worden de buizen uit reepen oud en zeer droog dennenhout zamengesteld, die in elkander gewerkt en door lijm aan elkander worden verbonden. Dan worden zij, in weerwil van hunne ontzaggelijke lengte, op een draaibank gebragt, volkomen rond gemaakt en eindelijk op de sierlijkste wijze met mahony bekleed.)). The original base was replaced in the 1930s by a metal one.(({{:telescopes:6-duims-mount.jpg?300|}})). The story goes that at the end of the 1930s, there was an astronomer who wished to observe an eclipsing star. The astronomer prepared the telescope. When he was ready to observe the star, he soon discovered that the only cloud in the sky that night just conveniently situated itself in front of his star. The astronomer became so angry that he kicked at the wooden base of the telescope and broke it. Now if people kick it they break their foot rather than the telescope :). This is a funny explanation that I would certainly tell when giving a tour. However, in the annual report of [[http://articles.adsabs.harvard.edu//full/1932BAN.....6..193D/0000195.000.html|1931]] the replacement of the wooden base by a steel one is explained by the fact that the wooden base severely limited the area of sky that you could observe convienently. I (Gilles) assume that the story of kicking the mount has some truth to it but it likely didn't happen in the end of the 1930s because by then the base would have been made out of iron. They did not only change the base while renovating the telescope. They also put a second smaller telescope on there which functions as finder or followscope and added an automatic tracking system. ---- ====Observing==== When you observe with the 6" telescope (and all the other telescopes we have) be mindful of yourself, the telescope, the visitors and your surroundings. Make sure you do not hit the telescope with anything and nothing hits the telescope. It has a great historical value and you do not want to be the person to break it. If something happens to the telescope, contact the WLS immediately and write it down in the logbook. However, the logbook is also meant for fun stuff so if you did some cool observing, please right down what you did! {{ :telescopes:weightdrive_6d_uitterdijk.jpg?direct&250|Weightdrive}}{{ :6duims.jpg?200|}} ===Short facts about the telescopes=== ^ ^ Main telescope ^ Finderscope ^ |Lensdiameter| 166 mm (6 Parish inches) | 70 mm | |Focal length| 2566 mm | 700 mm | |Field of view| Depends on eyepiece | 2 degrees | |Magnification | Depends on eyepiece | | === Set-up and tracking systems === * The telescope is placed on a German mount which means it has to be diverted in some cases (also called a meridian flip). Make sure you practice this by daylight! When you are planning to observe for a long time, it is important to make sure the telescope will not collide with the base and cause irreparable damage. * The tracking system or drive for the hour-angle is mounted to the base and can be turned on by plugging it into the socket. The brakes for the hour-angle are the two round screws on the ring where you can read off the hour-angle. DO NOT TURN THESE TOO TIGHT. They need to be tight enough to let the telescope follow along with the tracking system but no tighter. The same holds for the black knob that is the brake for the declination which can be found close to the eyepieces. * The hour-angle can be fine-tuned infinitely, with the flexible rod either from the left- or right side. The declination however only can be fine-tuned over a range of a few degrees. When at the end of its range, the declination has to be unlocked, the fine-tuning brought back to its middle position, and relocked again. This is a disturbance of the observations so check the position of the fine-tuning before you start. * Focussing can be done by turning the little wheel on the side of the eyepiece. * Be careful: the telescope is at the moment not very well balanced and may move a bit on its own. In general take care when moving the telescope, in order not to his visitors === The dome === * Only move and open the dome by using the wheels meant for moving and opening it. * Warn people when you are about to turn the dome. * Before opening the dome, make sure it does not rain and make sure you remove the pin. Put this pin on the table so you do not lose it. Don't forget to put it back in when you finish. * Always leave the dome with the opening facing towards the north/the roof. The reason for this is that the opening is also the emergency exit. You do not want people to fall of the roof while trying to escape. === Check before leaving === * Have I written my name in the Logbook? * Did I close the opening of the dome and leave it towards the north? * Have I left the telescope in the position that I found it? * Have I cleaned up the eyepieces and put the fillereyepiece back in? * Have I turned the heating (back) on? * Did I leave the hatch open? * HAVE I TURNED TO TRACKING SYSTEM OFF? (this one is very important) === Eyepieces === Eyepieces and zenith prism are stored in the small cupboard at the side. Focusing is done as usual. An inexpensive eyepiece is always left in the telescope as a cap. It is also good enough for showing a church clock in daytime. ^ F ^ Model ^ Magnification ^ |32 mm | Plössl | 70x | |15 mm | Plössl | 150x | |7-22 mm | WO Zoom | 100 – 320x | | - |Barlow | 2x | Note: More eyepieces, filters, and other peripherals are available for more specialized observations.