ìMň Armillary Sphere (1:1) P7 GɌ Ɍ ìň͈éƼP͵˲ɗňˢ ľ:C?·XZ#Z9YŹ XŹ·:ň%P ˊ9˥ɚƮoŅ=ϝŋ@365¼̑ 8oXƷ=ŋV°PVLc 7 GɌZɌůPʂčͦɌ:5o+βϏľŶƙ˲dz͔\#Ź·Yēň% #ɍD(ƙE ł-·365¼̀ɰŲ S9Ʒ=ŋ?ϟ LɌZL?ɌZͥ˛čͦɌůǩͦɌľ`5̌͵Cūɫƭ˛ƕ9Ź·Vͥň% PRȓƙ·365¼̑ Horizon Circle A horizontal ring with 4 wei, 8 gan and VͥoZPƭů͛Ͳ5CYēň9ūɫƭ˛ƕ Meridian Circle A vertical split ring along the north-south 12 zhi (totalling 24 cardinal points) Fìň͈ȴʙˊĭŁʔP~RɗǺ(=7ìňɒçĦµ̮ʌ"dzGÓɗȜ̑ direction with graduations of 365¼ degrees inscribed on the outer surface and 12 fenye on each side (As the ancient Chinese determined (kingdoms and regions) on the inner surface The Armillary Sphere is an astronomical instrument for that there are 365¼ days in a year, the full measuring the position of celestial objects. It comprises circumference of the sky is assigned as three sets of rings. The outermost one is called the 365¼ degrees) Liuheyi (Sphere of the Six Cardinal Points) which consists of the Meridian Circle, Horizon Circle and Fixed Equatorial Circle welded together securely on a supporting framework. The middle one is :ň the Sanchenyi (Sphere of the Three Stellar Objects) with its four components, namely, the Sphere of the Solstitial Colure Circle, Equinoctial Colure Six Cardinal Points Circle, Mobile Equatorial Circle and Ecliptic Circle joining together and rotating as a whole PʂčͦɌ around the polar axis. The innermost set which can rotate within the Sanchenyi around the .P̸čͦ polar axis is called the Siyouyi (Sphere of the \ŋVLòēEWŋ Four Movements) with the Hour-angle Circle, ̀XWŋo Celestial Axis and Sighting Tube. Fixed Equatorial Circle This is a replica of the Armillary Sphere of the Yuan Corresponding to the celestial Dynasty (1279-1368) which was reproduced in the equator with graduations of Ming Dynasty (1368-1644) and is currently locating at 100 marks for 12 double hours, the Purple Mountain Observatory in Nanjing. It has been so also called the ring of 100 marks adapted for use at the latitude of Hong Kong.
香港太空館制作produced by Hong Kong Space Museum ͤM( Operation IJ"òQ"͛^ª ʵʎǒįéƼP͵=ɗƥ͉ƕȭͥ˛čͦɌβ.ɗLV To measure the coordinates of a particular celestial object, we first use the Sighting Tube to locate the first determinative star to the west of the target. Then rotate the Mobile Equatorial Circle so that PɬT"͛Φ,ƿͥ˛čͦɌ̶ŝOɬ̑ĦVͥɌ̶ŝBɫ̑"ŝʑŇ the determinative star aligns with the mansion it belongs. After that, use the Sighting Tube to observe P̸Äƿ˲ the target star. Its celestial coordinates, namely, the “mansion extension” and “polar angle”, can then be read from the Mobile Equatorial Circle and the Hour-angle Circle respectively. L?Ɍ ǩͦɌ φơP̸ˊ9ɫůǩͦɌ .ǩͦɗƮo Pƭ 9Ʒ=?7ŋ@ ̈́?Mυ?Ġɗ8o ȴɫƭɗŅ˸ LVPɬMLVV˥ę Equinoctial Colure Circle ʕΉ͛ A ring passing through Ecliptic Circle Ň#^ƕȭ the celestial poles 9 A split ring Celestial Axis and equinoxes North corresponding of the Ecliptic to the ecliptic with A split bar along Circle 28 lunar mansions the polar axis allowing and 24 solar terms the Sighting Tube to LɌ marked on the turn on its centre ˊ9Ʈo inner surfaces φơǩͦɌ Vͥo ͥ˛čͦɌ M0Ġ ˊ ˊ9Ʈo South .P̸ ͛ Ņ=ʓP̸ˊɫǤ ʓP̸ˊɫǤŋ čͦ\ŋLVPɬ ʕ #NJ ŋ<ŲP1825/8̑ <ŲP1825/8̑ @ȓT(·ʍˢ Solstitial Colure Circle ɗůƥ̑ Hour-angle Circle A north-south split ring Mobile Equatorial Circle A north-south split ring Sighting Tube A rectangular tube intersecting with the solstices of Corresponding to the with graduations of 1825/8 Vͥň the Ecliptic Circle and having Yēň celestial equator with degrees for half circle with a circular hole 5 at the centre serving graduations of 182 /8 degrees for Sphere of the markings of the names starting from the ÄÅÆÇÈÇMÉÊMËÆÇ half circle which start from the and boundaries of south celestial pole as a pointing device south celestial pole on each side Three Stellar Objects the 28 lunar mansions ÌÉÍÈMÎÉÏÇÐÇÑËÒ
香港太空館制作produced by Hong Kong Space Museum #ɍD(ɗčͦÄƿùͫ"3Oɬ̑4ů3Bɫ̑4Ķƿ0#ɍɰPčͦʛʎ͉ɢ?· #ɍǰͫŴ.
LVPɬÈɬεEēƥ͉P͵ɗOɬ̶̶͈̑P͵Ä^ȟβʑɗƥ͉ɗčˬ¿B Traditional Chinese Naming for Directions
ɫ̑˄̶͈P͵ÄP̸9ɫɗnć North
9
In the ancient Chinese equatorial coordinate system, the positions are expressed in mansion qian
乾
gen extension and polar angle. Ancient Chinese divided the region along the celestial equator into 艮
zi
ren
gui 28 lunar mansions from each of which a determinative star is chosen as a reference. The mansion ren gui
癸 壬 V°
extension of a celestial object is the difference in right ascension between the object and its nearest hai
子
癸 壬
chou 4 wei (dimension)
determinative star to the west while its polar angle is the angle measuring from the north celestial pole. zi
xin 辛 qian 丑 亥
hai
甲 jia gen 子
chou
乾
P̸9ɫMNorth celestial pole 艮 P 丑 亥
xu 8 gan (stems or
yin
xu 寅
戌 Heavenly Stems)
PolarBɫ̑ angle
yin
寅 戌
xin
甲 辛 jia
P͵ West you you 卯 卯 Celestial 酉 酉 ȅ East mao object mao VLc geng 庚 乙 12 zhi (branches or
yi shen 申 辰 Earthly Branches) shen 申 辰 chen ƥ͉ 未 巳 坤 巽 chen LVV Determinative geng kun wei 午 star 庚 si 24 cardinal points
未 巳 yi čͦɌ wu xun 乙 Celestial equator wei 丁 丙 Oɬ̑ 午 si 丁 ding 丙 Mansion ding wu bing bing extension kun坤 巽 xun ˊ South
香港太空館制作produced by Hong Kong Space Museum ¨òē?·õõŋ #ɍǰͫòNJŴ. È_òē?·ʉZŅ_òͪÈͪV ŋEŋùEŋβʳdz:?&E ŋǜò Traditional Chinese Naming for Time ē@õõ ŋ
òēMýMÈòēòͪMýM ŋŋùMýMMýM1/6 ŋüMïMõõ ŋ M VLòēM 12 double hoursM ̺(òNJMùòü ( ) How to divide 12 double hours to 100 equal parts (ke)? time hour
Each double hour is divided into two hours: the initial and central one. Each hour is represented by 4 M M zi 23-01 big marks and 1 small mark (meaning 1/6 of a big mark). Therefore 12 double hours can be divided into 100 marks. M M chou 01-03 ( 1 ) 12 double hours x 2 hours per double hour x 4 big marks and 1 small mark 12 x 2 x 4 /6 = 100 big marks M ɩM yin 03-05
M @M mao 05-07
MēM chen 07-09 VLòē 12 double hours chou (01h-03h) zi (23h-01h) M M si 09-11 ʉ ʉ MGM wu 11-13 central initial central initial M M wei 13-15
M 'M shen 15-17
M ĞM you 17-19 ŋïM1/6 ŋ ŋ 1 small mark = 1/6 big mark 4 big marks M 3M xu 19-21
M 香港太空館制作produced by Hong Kong Space Museum Mʊ M Want to Know More Gnomon (1:2) The gnomon of the Ming Dynasty (1368-1644) was modified in theQing Dynasty (1644-1911) with an ʊ͈#ɍ D^b͈ ŧ8ɗP~ňˢ%3ʊ4ů34Ͳ5ʊ͈ɚ3ɗƿà increase in its height. Atop the gnomon was a copper leaf with a round pinhole. At noon, sun ray ͈ˊ9DZɗW"ĶƼ̑Rǐʙ²ʊòǒ±²ɗƇ ɗʕ̑ʊC"ĶéƙZE reached the gui through the hole so that the length of the shadow of the gnomon could be measured. As the height of the gnomon was increased, the gui was not long enough for measurement. So an -ɗʕ̑ZƜƙLVV˥ęɗ°ıFʊ͈ẵˊĭŁʔP~RɗǺ(ʊ=ç additional standing gui was erected at the northern end of the gui. Since then, the total length of the ͤM( gnomon’s shadow could be computed by simple geometry. E-#GƇ ʕɗ ͈0` ģɗ͈"ͮϋOʌ"dz9 łȣ"9 ʊƇʕ ȲγGÓϋĪdz9 łȣ"ˊɗȲƇ ģɗEPĦʠ total length of ʊȍ shadow of gnomon height of gnomon ɛEĠĠ ʕ ʊȍ 3Ƈȍ ̌±dz7cǺ(ǒçɗʊò¨ʊµȍ\@ě̐#NJLjEȓTGòRǐƇ length of gui height of gnomon height of shadow ʊ ˬͮȓT²ŏ=ʧCɚʵéƼʊƇɗʕ̑ʊ5ơ̏Äͨʑʕ̑"ďǒ"9 on standing gui biao (gnomon) N5E_3ǹŧ8ɗi <.ʧCˀ2ʊƇʕ The gnomon is the oldest and simplest astronomical instrument used in China. It is composed of a vertical biao (gnomon) and a north-south aligned ruler gui lying horizontally to measure the length of the gnomon’s shadow projected by sunshine. The gnomon can be used to determine the direction, length of a year and dates of the solar terms, etc. This is the replica of a gnomon produced in Ming ʊȍ Dynasty which is currently displayed at the Purple Mountain Observatory in Nanjing. 3 height of gnomon standing gui Operation The day at noon with the longest shadow is the winter solstice while the one with the shortest shadow 3Ƈȍ ʕ is the summer solstice. However, this only applies to the regions to the north of the Tropic of Cancer. height of shadow length of gui The day with the shortest shadow does not fall on the summer solstice for places located south of on standing gui the Tropic of Cancer like Hong Kong. Mgui ʊƇʕ total length of shadow of gnomon 香港太空館制作produced by Hong Kong Space Museum čͦ. Equatorial Sundial (1:1) 9 ù ü čͦ. A3'4 %=ůEăǼͲ5=@òNJŋ̑Ǽ˥ɚdz=čͦ. North ɗ=Ä̸čͦ=A=ɗDz˗ć̑·Hõ̑ÝBʳȜ̑ = GRǐ Horizon F͈ẵ9ĭ̀®Růɻˁɗčͦ=çĦ¹µʌ"dzGÓȜ̑ Direction of the Sun at noon during summer solstice ͤM( Ǽ Rǐʙ²ǼòO ʓ=\ɗ±ƇʧC̶ŝʳòɗòNJ̈́?υ?°NJRǐɤʙ² Stylus =ù9=ü`υ?̈́?°NJ˄ɤʙϟ=ùˊ=ü =ùčͦ=ü An equatorial sundial is composed of a template with time markings and a stylus erected perpendicularly Template (parallel to equator) to the template. The template is parallel to the equator, i.e. inclined at an angle of 90 degrees minus the 90˚- latitude. 90˚- latitude ɢ͗ This sundial is a replica of the one placed outside the Hall of Supreme Harmony in the Imperial Palace in Ȝ̑ Beijing with adaptation made by referencing to the latitude of Hong Kong. Latitude 0GRǐ Operation Direction of the Sun at noon Read the time from the shadow cast on the template as the Sun shines on the stylus. Between the vernal čͦ Equator during winter solstice equinox and autumnal equinox, the Sun casts its shadow on the northern face of the template. During the period between the autumnal equinox and vernal equinox, the Sun casts its shadow on the southern face. ˊ ̸ South Earth 香港太空館制作produced by Hong Kong Space Museum ɛEĠĠ gò¿ɡ̌ MEquation of Time Adjustment ?ʰMMinutes ʓʑ2ɗòNJ·3ŝRǐò4Äaμ̶0ɗƿʍòNJCƦ@ǒ"cϋ͈ ·ƿ 15 ʍòNJ ɭC"δ5͈E_Ŷ:ɗRǐčͦ="gϐ̑ͤĶ ` ̌_òȲ 9"cˬ̑ɗĠϝʳ(cEòNJ 10 ǒͯ0ɗˋ͈ŝɗRǐͤȭʡȯ̸ūRǐ<ƕɗ'ͦ·̛ȓͤϐ̑Ħ 5 "gıFX̸"fgh̑DzćūRǐ<ƕ̈́?Mυ?ĠʛʎRǐDz˗dzčͦͤ ̀ϋͤȭčͦ=ɗ±Ƈ͞gɗϐ̑`M0ʛʎRǐdzčͦ 0 ͤϋͤȭčͦ=ɗ±Ƈ͞gɗϐ̑AIJ¨cEòȲ9ɗȅϛȲÄϛȲ -5 ͞ȅϛɗRǐbɤ͞·ȡͯ0ɗòNJbɤ͞ -10 ¨ʓʑ2ɗŝRǐòƕ·aμǒ0ɗƿʍòNJʧǠ5O"\ŅǞ ƆAg ò¿Mˬ̑¿ɗɡ̌ -15 Want to Know More -20 123456789101112 The time obtained from the sundial is called the “true solar time” which may be different from the KMMonth watch time. This is because the watch time can be considered as a reading obtained from a fictitious aμòNJMïMòNJMuMgò¿ɡ̌MuMˬ̑¿ Sun moving along the equator at an average speed. In addition, different regions within the same time Watch time = Sundial time + Equation of time adjustment + Longitude adjustment zone have the same watch time. The sundial, however, displays the true motion of the Sun. The Earth orbits the Sun in an ellipse and thus at an uneven speed. In addition, due to the Earth’s axial tilt of 23.5 degrees, when the Sun P~<Ȓɗˬ̑·ȅˬgf̑ÄGÓòȲɗƿʍˬ̑ȅˬõ̑β¿hgw̑"fxõ̑ crosses the equator at both equinoxes, it is moving at an angle tilted to the equator. Therefore the βʳdzò ˬ̑¿·ugy?ʰ projection of this tilted motion onto the equator is slower than its mean motion. However, when the Sun is at both solstices, it moves parallel to the equator. Therefore the projection of this parallel ĵ wʓ\Ϗ͝ʑɗgò¿ϐ·ufgh?ʰ ͯ0ɗòNJ͈Gò˄ motion onto the equator is faster than its mean motion. Even within the same time zone, people in aμòNJ.·ZGòxgf?ùAòMuMfgh?ʰMuMgy?ʰü areas to the east would find that the Sun is in a more westward direction as compared to that viewed by people in areas to the west. So, the sundial time in the eastern part of a time zone would be faster The longitude of the Astropark is 114.3˚E, having a deviation of 5.7˚ from the standard meridian of Hong than that in the western part. Kong of 120˚E. As 360 degrees correspond to 24 hours, the longitude adjustment is +22.8 minutes. To convert the watch time from the true solar time, we need to make two adjustments as mentioned For instance, on 1 July, the equation of time adjustment is +3.5 minutes from the above graph. If the above, namely, the equation of time and longitude adjustment. sundial shows 12 noon, the watch time should be 12:26.3 pm (i.e. 12 hours + 3.5 minutes + 22.8 minutes). 香港太空館制作produced by Hong Kong Space Museum ͉M MStar Dial (1:1) ˥ęù°ü òŋ ͉XC͈ſNJ9"Φȩ͉́"ƙòŋɗE òņF͉͈ẵǺ(ɗ ͉̌ Solar terms (date) Time ǔ͟pxç(CʤxɈƦŌǰZĶ Kocab ͉%Ņ_c^ȓǺͲ5XǺŋ@òŋ9Ǻŋ@ŲP̑ƵVVL®"?LVV ˥ę#NJ@E˸(͉͛&" ͤM( jÄ IJ"òɰXǺ ʉŋùAGſü͛.ɗ9Ǻ˥ę̑Ƶ͛ȭěǺ9˦͉̌ùAjÄü Ursa Minor ÄC ͉ùAjÄǎ9ɫ͉üIJŅ͉c̺#Ǻ=ʠʊǒ̶ɗʧ͈ʳòɗòŋ The star dial, also called the pole-star dial, is an instrument for determining the time at night by observation of stars. This star dial is reproduced according to the records of the Ming Dynasty (1368-1644) but the original artifact was in existence no more. The star dial is composed of two concentric discs. The outer disc has time markings while the inner C ͉ disc has graduations of the circumference of the sky, listing the 12 zodiacs and 24 solar terms and Polaris having a slit for alignment of stars in the middle. 4P° Operation Today’s date i z l tia ni Align the central of the double hour zi (midnight, Chinese character is “ ”) of the outer disc with the l i ʫ tra cen suitable solar term of the inner disc. Turn the dial so that Kocab ( Ursae Minoris) and Polaris ʠʊ ( Ursae Minoris) can appear in the silt at the same time. The time could then be read from the Pointer pointer. 香港太空館制作produced by Hong Kong Space Museum ɛEĠĠ 9ɫ͉ʛʎɗ͉Ä jÄɤ"gϐϐòDū9ɫ͉˛ƕEɌ`͉ɗͤ(x <ƕ ̹ʧ͈̒ɕdz\(͉͵ͤĻNJ͉\gŋ\òŋ̑IJ"òO ˛ƕŏ. Revolution EP̛ ̧͉͞ˁEP ͉Äɗ˲ʧCʑ2òNJ ̸ɗ˲ :?ʰ2̺ "ͮ%dz̸ƕɗcòbɤ<ƕ͉ÄÈ˟bɤ͞ˁE˟:?ʰǨͨcE˲ Position of Earth The star appears 4 minutes F͉ 9"°ǺĶɡ˥ϋÈPɗòNJ¿̈́ after one day ſ earlier than it did G in the previous night Want to Know More Midnight Circumpolar constellations such as the Ursa Minor revolve around the Polaris once about every 24 hours. The star dial makes use of this motion and has graduations of 24 hours evenly marked on the dial surface so that turning the star dial for alignment with the Ursa Minor will tell the time. However, as the Earth has not only rotation but also revolution, constellations will appear 4 minutes earlier each night than the previous one. To correct this daily difference, it is necessary to adjust the ƕ star dial with the date (solar terms) dial. Rotation Rǐ Gſ 二十四節氣M Solar TermsM 日期MM Date 二十四節氣M Solar TermsM 日期 M Date Sun Midnight 3̈́M Spring Commences M 4 FebM 3υM Autumn CommencesM yyM 8 Aug ʞM Spring ShowersMHM 19 Feb ΞªM End of HeatM yfM 23 Aug ̸ ͱࢳM Insects WakenM fxM 6 Mar )́M White DewM HyM 8 Sep Earth ̈́?M Vernal EquinoxM fM 21 Mar υ?M Autumnal EquinoxM HfM 23 Sep ̌ǺM Bright and ClearMhM 5 Apr ÝM Cold DewMõyM 8 Oct ȊʞM Corn RainMõM 20 Apr ď 香港太空館制作produced by Hong Kong Space Museum M MMoon Dial (1:1) Want to Know More The Moon rises and sets daily like the Sun due to the Earth’s rotation. In addition, the Moon revolves XR͈ϖͮΦé̸˲`ʑ2òŋɗ òňˢF͈ẵ̺"dz9ĭ around the Earth, resulting in its appearance delayed by an average of 48 minutes each night. ̀®ȷϧ®ɗɒç`5 However, as the orbit of the Moon is an ellipse and the orbit is tilted, the time of moonrise and moonset can vary greatly from day to day. Therefore adjustments must be made in accordance with ephemeris %Ņ_c^ȓǺů#^ͥʊSY_ϛ?Ͳ5ZǺ·òŋǺŋ@VLòē\Ǻ· so as to use the moon dial accurately. βǺŋ@fõPMfxõ̑Ħõ̑˲\"2Eɚʊ ͥʊ ͤM( Vernier IJ"òQȂƙɗˊ9M̹Ȝ̑Tȴʙ+ƥˬ̑ʊ,ɰͥʊŶƙβǺ ɗβ.˲ư̂"ɚʊʃȭ ͥʊÄβǺcòƕȭͥʊÄ̸5Eɚȣòʓɚ ̸ ʊòŋǺ\ǒ̶ɗ˲̶ŝòŋ ɚʊ G noon 12:00 Pointer Moon ɛEĠĠ 0˚ βǺ û ̸ȆKÈP ̸ƕ`ȅH̋Xbɤ Dū̸<ƕ˲Ϧ͞ˁE˟gζ2y? Moon phase disc New Moon ʰ"ͮ%dz̸ɗ'ͦM̛ȓ5\^Ä̸ɗ'ͦ5nć"Ϧ̸ɗ2ØòNJ \ƶ First ÈPbC"β¿̖ FǠẵ͍ï(2cư̂ CÉ2͞ʍȂɗòŋ 6:00 Quarter Zƶ 90˚ Third Quarter 270˚ 18:00 The moon dial or lunation dial was a chronometer based on observation of the position of the Moon. This one is a replica of the instrument displayed outside the Palace of Benevolent Tranquillity in the Imperial Palace in Beijing. òŋǺ ˦M Full Moon The moon dial is composed of two concentric discs and a vernier. The lower disc is the time disc with Time disc 180˚ graduations of 12 double hours. The upper disc is the Moon phase disc with markings of 30 days and 360 degrees. A pointer extends from the location at zeroth degree. G ſ midnight 0:00 Operation 90˚-ɢ͗ Align the moon dial along the meridian and adjust to the correct latitude. Rotate and fix the vernier at 90˚- latitude 9 ˊ the corresponding degrees on the Moon phase disc according to the table of lunar angular distance to the Sun. Then turn the Moon phase disc and the vernier together by the pointer until the vernier North South aligns with the Moon. The time can then be read along the pointer on the time disc. 香港太空館制作produced by Hong Kong Space Museum IMň Upward Looking Bowl Sundial (1:3) Iň͈7(P~˰¬Ϝ$ə"çɗP~ňˢ""ΦéRǐ"ƙòŋMΦéE Iň ͵͈E_ɚÇϐfYɗ#ɢ≮@ EȉIDZɗÿ ňȶŋ@LVV9 ́Ȏ ˩ŋ@čͦÄƿ©Iňˊ@EɚÃ"#^̮@EȝCˊ9Mȅƕȭɗ́ Rotatable plate ȎȎ#@ET.Iňɗ#^Ġ West ͤM( Φéòƕȭ́ȎÄǐN˥ɚɗ˲RǐύͮT5γdzÄƿ©\ʓ`ɚʵ̶ŝR ˊ ǐɗ˲ÄƿĦé2ŝRǐòFXEòϖͮǼT5γČɧΦéEɗͮĩ South éƙE?MEβɗòŋůï3 "é͑ɚʵΦδ̱ĸɗǐN čͦ Equator The upward looking bowl sundial was an astronomical instrument designed by the astronomer Guo Shoujing of the Yuan Dynasty (1279-1368) for observation of the Sun to determine the time and for viewing of solar eclipse. 9 North The main body of this sundial is an empty hemispherical bowl facing upwards which is around 3 metres in diameter. The rim is engraved with 24 cardinal points and the inner wall with a grid of equatorial coordinates. A rod extends from the southern rim to the centre of the bowl with a rotatable plate at the end which can turn along the north-south and west-east directions freely. The plate has a small hole corresponding to the centre of the sundial. Operation ȅ Turn the rotatable plate until it is perpendicular to the Sun so that the sunlight passes through the East hole and projects on the grid. The position of the Sun and the true solar time can be read directly from the grid. During solar eclipse, the progress, magnitude and time and position of different phases can be measured easily with the projection on the grid. The hazard of looking at the bright sunlight directly can thus be avoided. 香港太空館制作produced by Hong Kong Space Museum ÄčͦEƺʓ̶ŝɗòNJ͈ŝRǐòǠ cgò¿ůˬ̑¿ ɤʑ MHorizontal Sundial (1:1) 2aμ̶0ɗòNJ %ɗ=ůDz˗ɗǼͲ5YćȎɗ˗=ǤŧǼɗ("̶9Pɫ Just like the equatorial sundial, the time obtained from the horizontal sundial is the true solar time. ϋ͈ẵˊĭŁʔP~RɗǺ(=7Ϝ$əŧň\ɗɒç`5 Adjustments in equation of time and longitude have to be made to give the watch time. ͤ( ΦéYć˗==\ɗRǐ±ƇʧCʑ2òNJ gò¿ɡ̌ MEquation of Time Adjustment ɛEĠĠ 9Pɫ ?ʰMMinutes óÉÈËÆMôÇñÇÒËðïñMÅÉñÇ 15 Ĭ\͈¨čͦɗ=±ƇE=\ǒ"=ɗ òNJȣĦʠg?/ čͦ 10 íîÍïËÉÈðïñMÒÍÑòðïñ The horizontal sundial is composed of a horizontal template and an inclined 5 stylus. The inclined side of the triangular plate acts as a stylus pointing at 0 the north celestial pole. This instrument is a replica of the horizontal sundial of the simplified armillary sphere designed by the astronomer -5 Guo Shoujing of the Yuan Dynasty (1279-1368) which is now placed at the Purple Mountain Observatory in Nanjing. -10 Operation Ȝ̑ -15 Time can be obtained by observation of the projection ÷ïËðËÍòÇ -20 of the inclined plane on the template. 123456789101112 KM Want to Know More Month ˊ aμòNJMïMòNJMuMgò¿ɡ̌MuMˬ̑¿ùgy?ʰü Actually, the horizontal sundial is a 12 ÄÉÍËÆ Watch time = Sundial time + Equation of time adjustment + Longitude adjustment (22.8 minutes) projection of an equatorial sundial on a horizontal surface. So the time 13 markings on the template are 14 õÉÈðöÉÑËïñMÒÍÑòðïñ not evenly distributed. 18 17 16 15 香港太空館制作produced by Hong Kong Space Museum The direction determining table is an astronomical instrument designed by the astronomer Guo Ā MDirection Determining Table (1:1) Shoujing of the Yuan Dynasty (1279-1368) to determine the direction and latitude. Ā͈%7(P~˰¬Ϝ$ə"çɗP~ňˢ""éƙMȜ̑ It is a square plate surrounded by a trench for levelling. A pole is erected at the centre. A total of 19 concentric circles of equidistance are engraved on the plate. Ā·EȝȎŲD@Ú"ƙ#^ιEéƇɗƫùÃü#^Ǥē@ H_ıƥɗc^ȓ Operation ͤM( To determine the direction, lay the table horizontally. After sunrise in the morning, mark the intersection formed by projection of the pole top and the outermost circle to the west. One after éƙòQ¨ĀijDZ\G2̛̗ƫ ɗƇÄ XɌ=β: another, mark all intersections formed between projection (shadow) of the pole top and all the òβ:ĠȘEƿǔư̂įEʳƫ ƇÄX͡LɌZ͡YɌıɌβ:ògEE concentric circles. Similarly, mark all intersections made between the circles and projections of the pole top to the east in the afternoon. Lastly, join the two intersections on each circle for all 5"ƿǔcƺȅ=ɗƇG̛ÄγɌβ:òb \(2ƿǔ ̛¨È_γɌ the 19 circles. Bisect the lines and join their mid-points will give a line showing the north-south ȅŅƿǔβϏŝ#NJ˲Ϗȣʧʑ2ˊ9 #GRǐ direction. éƙȜ̑òĀ #^ē P̸čͦ The Sun at To find the latitude, draw two perpendicular lines representing the pole line and the equator at the centre of the table. Then draw two lines parallel to the equator line on each side with a Ņ˸: ɚ ȣ ?7(ʊ Pɫ Celestial equator summer solstice separation equal to the inclination of the ecliptic. Each of the lines will intersect with two points MPčͦT̰ǩč:ć on the outer circle, representing the directions of the Sun at summer and winter solstices. Hang 0#GRǐ ǩč:ć čͦ\Z Ȋ Eȣ the table vertically along the meridian plane. At noon on either solstice, attach three pegs The Sun at ÄγɌβ:dzŅĠÈĠ?7 Inclination of separately at the centre of the table and the two intersecting points. Rotate the table on the winter solstice (ʊZ0LòRǐɗ the ecliptic centre until the shadows of the three pegs align. The then inclination of the pole line is the latitude. ¨Ā ˥ɚɲʾ P̸9ɫ G=Ħdz0ǎ # éƙȜ̑ North celestial pole éƙ GòĀ #^MγɌβ: Ġ Finding Determining E½ "Ā #^·ƭ^ 9 the Latitude the Direction N ƕȭĀ IJY½ ɗ Ƈ 7 ̪ 9ɫȣ ɗ ȍ ̑ʧ ͈ʳ Ȝ̑ Ȝ̑MLatitude 香港太空館制作produced by Hong Kong Space Museum M͵ MHuman Sundial Ʈ̂?7ž#ȣɗbE.ʳPɗKʓĐ͵ɗ±Ƈ̶ŝòNJ Stand with one foot on each side of the centre line at the current month. Then read the time from your shadow. ?ʰ MMinutes gò¿ɡ̌ MEquation of Time Adjustment 15 10 5 0 -5 -10 -15 -20 123456789101112 KMMonth aμòNJMïMòNJMuMgò¿ɡ̌ ùˬ̑¿M͵ɗŋ̑c̷ʡCȴδčͦ.ü Watch time = Human sundial time + Equation of time adjustment (Longitude adjustment is already made on the time markings of the human sundial. Please see the equatorial sundial for details) 香港太空館制作produced by Hong Kong Space Museum