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(25.18°N 121.53°E, 828m, Clear midnight SQM@Alt 45° N<avg. 19.9>/ S<avg. 19.4> Bortle scale 5)
左起Nikon Monarch 10x56, Pentax 75SDHF (3"), Takahashi FC-76(3"), Pentax 105SDHF(4"), Skywatcher 150(6"), Takahashi Mewlon-210(8.3")
※眼視對比門檻值會隨著每次觀測的條件而有所變化，因此Difficulty level 也可能變動。會影響門檻值的有觀測使用的口徑、倍率、濾鏡、觀測時天體的仰角及天空背景亮度，以及天空透明度。The visual contrast threshold may vary with each observation condition, hence the difficulty level can also fluctuate. Factors affecting the threshold include the aperture and magnification used for observation, filters applied, the elevation angle of the celestial body during observation, the brightness of the sky background, as well as the transparency of the sky.
※下拉選單無法於內崁文件中使用，所以無法在此使用測試功能。 The drop-down menu cannot be used in embedded documents, so testing cannot be done here.
※觀測皆以眼視手動對照星圖尋找深空天體。手動尋星沒有困難。 Observations are made by manually comparing star charts to locate deep-sky objects. Manually finding deepsky objects is not difficult.
※本資料庫雖於鞍部建立也適用於在同樣有Bortle 5等級或更暗的夜空地區觀星参考。 Although this database was established at AnBu, it is also applicable as a reference for stargazing in areas with Bortle 5 or darker night skies.
※［下載 download］Yangmingshan Anbu(Bortle 5) 300 Deep Sky Objects 觀測清單（Skysafari List .skylist格式）。
※ (2023)NEW 資料庫深入圖表分析，觀測建議 （請點選連結） In-depth analysis of the database. ：
(Part 1) Variation characteristics of the sky surface brightness at Anbu.
（2）鞍部三百個深空天體觀測數據分析- 星系、星雲的眼視觀測 /extended objects(Part 2) Analysis of the observational data of the 300 objects, including analysis of visual threshold of extended objects such as galaxies and nebulae.
（3）鞍部三百個深空天體觀測數據分析- 星團的眼視觀測(part 3) Observation of Clusters
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數據分析 Data analysis
classification by size
從350個深空天體的大小統計圖可見，絕大多數都小於60'，大於90'僅16個，其中超過兩度的更只有七個。
From the size statistics chart of 350 deep-sky objects, it can be seen that the vast majority are smaller than 60 arcmin, and only 16 are larger than 90 arcmin. Among them, there are only seven that exceed two degrees.
*這個值並非是天頂的SQM數值而是觀測某天體時指向該天體的天空背景SQM值，所以是包含四面八方各仰角的數值，如果你的觀測次數夠多，應該會得到接近的結果（觀測目標大多不會是在最暗的方位與時間）。
* This value is not the SQM value at the zenith, but the SQM value of the sky background pointing to the deep-sky object being observed. Therefore, it includes values at all angles and elevations. If you have enough observation data, you should get similar results (the observation targets are mostly not in the darkest direction and time).
*300下方標示27表示使用最高倍率介於150至300間的共有27個深空天體
*27 is marked below 300, indicating that there are a total of 27 deep sky objects using the highest magnification between 150 and 300.
可以輕易看出在筆者於鞍部的小型望遠鏡（8"以內）深空天體眼視觀測中，最常使用的倍率在 80與 150倍（根據使用者的望遠鏡焦長與目鏡焦長的規格，有可能無法完全參考複製這個倍率值，但仍可得到接近的倍數。）。請參考資料庫統計圖表分析，裡面有關於使用倍率的更詳細的統計與說明。
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355 Objects 以天體大小分類，並簡單分為：
星團星體 cluster&stars、
星系 galaxy、
星雲 nebula
- 有(r)記號為反射星雲，(OC)為疏散星團，(PN)為行星狀星雲。 關於M天體與NGC天體介紹請參考messier-objects.com、 wiki Messier objects ＆ NGC、Finest NGC Objects
- 有✭ 符號的是個人認為草山目視必看的精彩天體 (Most spectacular deep sky objects for visual observing at Yangmingshan )。
- 有鏈結的天體是至少有過一次素描的（可直接點選以下天體編號瀏覽素描與眼視觀測日誌， click the object number to see sketch and journal），共計有300個（2022/09/01）。請注意素描的視野會因望遠鏡的光學結構與有無天頂鏡而方向有所不同。
Linked objects have been sketched at least once (click the object number to see sketch and journal), totaling 300 as of September 1, 2022. Please note that the field of view of the sketch may differ in direction due to the optical structure of the telescope and the presence or absence of a Star diagonals. - 球狀星團以及星系的實際眼視大小會比標稱的大小還小許多，請參考統計圖表中以r_h, r_eff的分析
The actual visual size of globular clusters and galaxies is much smaller than their apparent size listed in wiki. Please refer to the analysis in the statistical charts using r_h and r_eff.
NGC40,NGC1501,NGC1535,✭NGC2392,NGC3132,✭NGC3242,NGC6302,NGC6445,✭NGC6543,NGC6572,NGC6818,✭NGC6905,✭NGC7009,NGC7027,NGC7662,NGC4361, NGC2440, NGC6210, NGC6153, NGC6565, NGC6537, NGC6741, NGC6751, IC4846,NGC6567 (全都是PN) (25/25)
介於1’與10’間的共175個 ：
M2. . ✭M4, M9, M10, M12, M14, M18(OC), M19, M24(OC), M26(OC), M28, M29(OC), M30, ✭M36(OC), M40(Multiplestars), M53, M54, M55, M56, M62, M68, M69, M70, M71, M72, M73(OC), M75, M79, M80, M93(OC), M103(OC), M107, NGC559(OC), NGC654(OC), NGC1502(OC), NGC2129(OC), NGC2169(OC), NGC2362(OC), NGC2343(OC), NGC2482(OC), NGC5053, NGC5986, NGC6144, NGC6242(OC), NGC6268(OC),NGC6281(OC), NGC6388, NGC6440, NGC6541, NGC6604(OC), NGC6712, NGC6723,NGC6356(OC) NGC6939(OC), NGC6989(OC), NGC6997(OC), NGC7510(OC),M32,M49,M58.M59, M60,M61,✭M64,✭M66,M74,M77,✭M84.M85.✭M86,✭M87,✭M88,M89,M90,✭M91,M95,M96,M98,M99,M100,M102,✭M104,M105,✭M108,M109,NGC289,NGC1232,NGC1300,NGC1374,NGC1379,NGC1380,NGC1381,NGC1386,NGC1387,NGC1389,NGC1399,NGC1404, NGC1541,NGC2841,NGC3371,NGC3373,NGC3593,NGC3877,NGC3893, NGC3896, NGC3949, NGC3953,NGC4038,NGC4096,NGC4214(NGC4228), NGC4216, NGC4312, NGC4388, NGC4394, ✭NGC4435, ✭NGC4438, ✭NGC4443,NGC4449,✭NGC4458, NGC4459, NGC4473,NGC4477,NGC4485,NGC4490,NGC4494, NGC4526, NGC4535, NGC4560, NGC4567,NGC4568,NGC4666,NGC4725, NGC5146,NGC5195,NGC7331, NGC4474, NGC4667, NGC4564 , NGC5907, NGC4559 (77/83)
✭M1,✭M27(PN),✭M57(PN),✭M76(PN).M78(r),✭M97(PN),NGC246(PN),NGC1333(r),NGC1360(PN),NGC1491,NGC1788(r),NGC1931,NGC2071(r), ✭NGC2261, ✭NGC2359,NGC2438(PN), NGC2467,✭NGC2818(PN), NGC6302(PN),NGC6781(PN),NGC6826(PN),NGC7538,IC63,IC1284,IC4685,IC428,Barnard 93,Jones-Emberson(PN) 1, NGC1514(PN), ARO 174 (PN) (24/30)介於11’與40’間的共109個 ：
✭M6(ButterflyCluster (OC), M3 ,M5, ✭M11(OC), ✭M13, ✭M15, M21(OC), M22, M23(OC), M25(OC), M34(OC), M35(OC), M37(OC), ✭M38(OC), M39(OC), M41(OC), ✭M46(OC), M47(OC), M48(OC), M50(OC), M52(OC), M67(OC), ✭M92, ✭NGC457(OC) ,NGC663(OC), ✭NGC869(OC), ✭NGC884(OC) 英仙座雙星團, NGC1245(OC), NGC1528(OC), NGC1545(OC), NGC1647(OC), NGC1893(OC), (NGC1973 r,NGC1975 r,NGC1977 OC), NGC2244(OC), NGC2264(OC), NGC2360(OC), NGC2395(OC), NGC2423(OC), NGC6124(OC), NGC6231(OC), NGC6530(OC), NGC6625(OC), NGC6633(OC), NGC6940(OC), NGC6996(OC), NGC7209(OC), NGC7243(OC), ✭NGC7789(OC), IC4756(OC), Stephenson1(OC), Trumpler 2(OC), ✭NGC5139(ω Cen), Cr428(oc)(51/55)
✭M51,✭M63,✭M65,✭M81,✭M82,✭M83,✭M94,M101,M106,M110,NGC247,✭NGC253 Silver Dollar, NGC891, NGC1316, NGC1365, NGC2403,NGC2903,NGC3628,NGC4244,NGC4565,✭NGC4631,NGC4656,NGC5128,NGC5907,NGC6822,NGC6946,(25/26)✭M16,M20,✭M43,✭NGC281,NGC2024,NGC2174,NGC6334 ,NGC6888,NGC7023(r),✭NGC7293 Helix(PN) , NGC7635, IC59, IC405, IC410, IC417, IC1283,IC1318,IC4605,IC5146,Gum 68(sh2-13),Gum 70(sh2-16),Sharpless 2-132, Barnard 352,Barnard 353, Medusa Nebula - Abell 21(PN),CB 125(DN), Running man(Sh2-279),Sharpless 2-308(海豚) (13/28)介於41’與69’之間的共24個：
✭M17(46'x37'),NGC2264(60'x30', 錐狀、聖誕樹等),NGC6357(50'x40', 龍蝦),NGC6974, NGC6979 Pickering's triangle (60'),✭NGC6992+ NGC6995(66', Eastern Veil Nebula), NGC7822(60'x30'),IC434(60'x10', 馬頭),IC443(50'x40',水母),IC4604(60'x25',),Sharpless 2-54(60'x30'),Sharpless 2-311(50'x30'),Sharpless 2-9(60'x50'), Sharpless 2-157(60'x50'),Cave Nebula - Caldwell 9(50'x30'),Cederblad 214(50'x40'), (5/18)✭M31(189'x62'),是除麥哲倫雲外離我們銀河系最近的星系，距離約250萬光年。(1/1)✭M8(90'x40'),✭M42(85'x60'),NGC1499(145'x40', california),✭NGC6960( Western Veil, 70'x6'), ✭NGC2237,2239(80'x60', Rosette), NGC7000(120'x100', North America),IC1396(170'x140', Elephant's Trunk), IC2118(180'x60', Witch head，非常暗淡的反射星雲。困難目標), ✭IC2177(120'x40', Seagull海鷗), IC4628(90'x60', 斑節蝦 Prawn Nebula), IC5070 (80'x70', Pelican 鵜鶘), Barnard's Loop - Sharpless 2-276(600'x30'), Antares Nebula - van den Bergh 107(85'x80', 星空調色盤), ✭ IC1805(180', 心),✭IC1848(120'x90',靈魂，心與魂皆大於兩度) (10/15)已眼視素描的300個天體視大小統計 (2022/09/01)
*目前我觀測過的最遠天體是類星體 3C 273（2023／07／08），距離我們有24億光年之遙。它是透過8"小鏡在郊山所能見到的最遠天體。
*NGC天體表（New General Catalogue of Nebulae and Clusters of Stars）是由約翰·德雷耳(John Louis Emil Dreyer) 於1888年根據威廉赫歇爾父子的觀測資料所編纂的天體目錄，收錄了星系、星團和發射星雲等共 7,840個深空天體。德雷耳在1895年和1908年又分別出版了兩份 NGC的補充資料，稱為索引目錄即IC catalog （ Index Catalogue of Nebulae and Clusters of Stars），新增了5,386個天體，IC星表大部分是通過攝影發現的，其中有許多發射星雲在光害區很難以小型望遠鏡眼視。
The NGC (New General Catalogue of Nebulae and Clusters of Stars) is a celestial catalog compiled by John Louis Emil Dreyer in 1888 based on the observation data of William Herschel and his son. It contains a total of 7,840 deep-sky objects such as galaxies, star clusters, and emission nebulae. Dreyer published two supplements to the NGC in 1895 and 1908 respectively, called the Index Catalogue of Nebulae and Clusters of Stars (IC catalog), which added 5,386 celestial objects. Most of the IC catalog was discovered through photography, including many emission nebulae that are difficult to observe with small telescopes in light-polluted areas.
Sharpless 目錄為美國天文學家 Stewart Sharpless於1953年所編攥，只收HII區天體即發射星雲（也包含行星狀星雲與超新星殘骸），在1959年第二版時共收錄了313個天體，這些天體中有些已有NGC或 IC編號。在筆者的鞍部300個眼視素描列表中如果天體同時被收錄在不同目錄中，筆者使用的天體編號順序是M, NGC, IC, Sharpless , 也就是說如果一個天體同時具有梅西爾編號與Sharpless編號，那麼就會列在梅西爾天體中，所以上面表中所列的Sharpless天體都不在前三者的目錄中，幾乎都是非常黯淡的發射星雲。
The Sharpless catalog is compiled by American astronomer Stewart Sharpless in 1953 and only includes HII region celestial objects, i.e. emission nebulae (including planetary nebulae and supernova remnants). The second edition in 1959 included a total of 313 deep-sky objects, some of which already have NGC or IC numbers. If a celestial object is included in different catalogs, the author's order of celestial object numbers used is M, NGC, IC, Sharpless. Therefore, if a object has both a Messier number and a Sharpless number, it will be listed under Messier objects. Therefore, none of the Sharpless objects listed in the table above are in the catalogs of the first three. They are almost all very dim emission nebulae.
*粉紅色的字體的，是較困難的眼視目標(pink: invisible or difficult)，集中於星雲部份，主要是IC、Sharpless 天體與暗星雲。建議在做觀測計劃時可把這些目標放在中後段，避免一開始卡關容易讓整個觀測變得急躁。（NGC5146是距離我們有3.15億光年的橢圓星系，視星等只有14等）除了粉紅色目標以外，若您參考使用資料庫內同樣口徑、倍率、濾鏡等來觀看，應該十之八九都能看到，少會有因人而異的情況。
The pink font indicates objects that are more difficult to observe, mainly IC and Sharpless objects, as well as dark nebulae. It is recommended to place these targets in the middle or later part of the observing plan to avoid becoming frustrated at the beginning of the observation. (NGC5146 is an elliptical galaxy located 315 million light-years away from us, with a visual magnitude of only 14.)
Except for the pink targets, if you refer to the same aperture, magnification, and filters in the database, you should be able to see almost all of them, with very few individual differences.
*疏散星團多分佈在銀河的盤面上，球狀星團則是集中位於銀暈之中；在我們銀河系中已發現的球狀星團約有一百多至兩百個之間，疏散星團則較多，已超過一千個。金牛座畢星團 (Hyades ) 是距我們太陽系最近的疏散星團，距離約150光年，天蠍座的M4則是離我們太陽系最近的球狀星團，距離約7200光年，巨爵座的Laevens 1是目前發現的屬於銀河系的最遠的球狀星團，距離約47萬光年。我們的銀河系外觀依哈伯分類屬棒旋星系，直徑估計約十萬至十八萬光年，太陽距銀河中心約二萬七千光年。星系由數千萬至上兆顆恆星組成，可見宇宙中約有上千億個星系。進一步的有關球狀星團的豐富參數包括CM圖請參考此gobular cluster database(必須使用NGC編號查詢)。
The open star clusters are mostly distributed on the disk of the galaxy, while the globular star clusters are concentrated in the halo. There are about 100 to 200 known globular clusters in our Milky Way galaxy and more than 1,000 open star clusters. The Hyades is the closest open star cluster to our solar system, approximately 150 light-years away. M4 in Scorpius is the closest globular cluster to our solar system, approximately 7,200 light-years away. Laevens 1 in Ursa Major is currently the farthest known globular cluster in our galaxy, approximately 470,000 light-years away. Our Milky Way galaxy has an estimated diameter of about 100,000 to 180,000 light-years and is classified as a barred spiral galaxy according to the Hubble classification. It consists of millions to trillions of stars, and there are approximately hundreds of billions of galaxies in the observable universe.
*在這裡八吋在中高倍時極限星等輕易可達13等以上，使用星圖建議使用支援到14等的星圖。*以上，在個人選編清單時（進一步說是過去在使用Astrotracer 拍攝時），最初的目的是想調查，在這裡（鞍部）兩分內鐘的曝光下能看到哪些天體，於是便有了此表，然後進一步進行目視素描觀察。此清單設定為在大於1'的天體中選取，除了一些較亮的行星狀星雲。這裡備忘幾個比較特別的尚未列入清單的星系：1.史蒂夫五重星系NGC 7320c(0.7’x0.6’),NGC 7319(1.7’x1.3’),NGC 7318a+NGC 7318b(1.9’x1.2’),NGC 7317(0.4’x0.4’)。2.NGC 226 (0.8'x0.8')
The author's list was originally created to investigate which celestial objects could be seen within two minutes of exposure here (Anbu), and then further observed by eye. The list is set to select deep-sky objects greater than 1', except for some brighter planetary nebulae. There are a few special galaxies that have not been added to the list: 1. Stephan's Quintet NGC 7320c (0.7'x0.6'), NGC 7319 (1.7'x1.3'), NGC 7318a+NGC 7318b (1.9'x1.2'), NGC 7317 (0.4'x0.4'). 2. NGC 226 (0.8'x0.8').
*眼視看到的天體大小可能會與星圖提供的參考資料有出入，同一目標於不同軟體與資料庫間的資料也可能不同，銀河外的星系亦可參考The Extragalactic Distance Database (EDD)、HyperLeda、NED(NASA/IPAC Extragalactic Database)。此外，星圖軟體的天體赤道座標位置也可能有出入，若搜尋時對於天體位置有疑問請參考權威的星圖譬如 URANOMETRIA 2000.0 星圖以確認手上星圖的座標正確性（譬如已知 Skysafari 的Sharpless目錄中有些目標的赤道座標/標示位置有誤）。The size of deep-sky objects observed visually may differ from the reference data provided in star charts. The data for the same target may also vary between different software and databases. For extragalactic galaxies, you can refer to The Extragalactic Distance Database (EDD), HyperLeda, and NED (NASA/IPAC Extragalactic Database). In addition, the equatorial coordinates of celestial objects in star chart software may also vary. If you have any doubts about the position of celestial objects when searching, please refer to authoritative star charts such as the URANOMETRIA 2000.0 star chart to confirm the accuracy of the coordinates in your star chart (for example, some of the equatorial coordinates or labels of Sharpless targets in Skysafari's catalog are incorrect).
*對於行星狀星雲、發射星雲與超新星殘骸來說可嘗試使用OIII或OIII+H-beta濾鏡，尤其對行星狀星雲特別有效。使用OIII濾鏡約可降低天空表面亮度2~2.5 mpsas ，也就是在SQM有20的郊山透過OIII濾鏡看到的天空背景亮度會相當於在高山裸眼觀看的天空暗度（未包含倍率減光的效應），若發射星雲的光線集中在濾鏡通過的波長，相對地減到天體的亮度很少，天體與背景天空的對比因此增加，效果會非常顯著。應該可以這麼說——
OIII或OIII+Hb濾鏡是觀賞發射星雲、行星狀星雲、超新星殘骸必須要準備的，絕對有幫助（請參考光害與濾鏡專頁）。
For planetary nebulae, emission nebulae, and supernova remnants, you can try using OIII or OIII+H-beta filters, especially for planetary nebulae, which are particularly effective. Using an OIII filter can reduce sky brightness by about 2-2.5 mpsas, which means that the sky background brightness seen through an OIII filter in a suburban area with an SQM of 20 is equivalent to the sky darkness seen with the naked eye in a high mountain area (without considering the effect of magnification reduction). If the light from an emission nebula is concentrated in the wavelength passed by the filter, the relative reduction in the brightness of the object is very small, and the contrast between the object and the background sky is increased, resulting in a very significant effect. It can be said that OIII or OIII+Hb filters are necessary for observing emission nebulae, planetary nebulae, and supernova remnants, and they are definitely helpful (please refer to the light pollution and filter pages).
唯需注意經OIII窄頻攝影調查（2019/04/18止），表中近20個發射星雲缺乏OIII波長的光，這些星雲是困難目標，可列為H-beta 嘗試的對象。請參考發射星雲的OIII影像database 。
Please note that as of the OIII narrowband survey (as of 04/18/2019), almost 20 emission nebulae in the table lack OIII wavelength light, making them difficult targets. These nebulae can be listed as targets to try with H-beta filters. Please refer to the OIII image database of emission nebulae.
打勾的是已經有眼視素描的天體，其他的除了零星幾個是錯過觀測窗口而漏掉的以外都是OIII非常弱，灰色字體的天體則是幾乎看不見OIII的。
The checked boxes represent celestial objects that already have visual sketches. Except for a few scattered ones that were missed due to the observation window, the rest have very weak OIII signals. The celestial objects in gray font are ones where OIII is almost invisible.
*一般來說，使用者只要熟悉Star hopping 並經過多次實際找星觀測經驗後，使用Star hopping 找任何天體應該都沒什麼問題，也不會花很長時間。如果真Star hopping 找不到，或尋星視野比較小時，刻度導入的方式便可以派上用場。
*Generally speaking, as long as the user is familiar with star hopping and has had multiple experiences of actual star-finding observation, there should be no problem using star hopping to find any celestial object, and it shouldn't take too long. If you really can't find it with star hopping or if the field of view for star searching is relatively small, the method of introducing scales can come in handy.
*通常會在尋星過程中迷向的原因主要有以下幾種可能：1. 尋星鏡或望遠鏡視野與星圖方向不同，譬如目鏡中所見視野已翻轉，可是觀測者本身並未意識到未將星圖翻轉或設定翻轉的方向錯誤。
2. 觀測者對望遠鏡搭配特定目鏡所得的實視野設定錯誤，導致無法將所見視野內的恆星與星圖比對起來。
3. 星圖本身標示目標的位置錯誤。
4. 觀測者沒有確實先確認比對星圖與目鏡視野方向的一致，導致認錯預設的錨星而走錯下一步。
*There are several possible reasons why observers may get lost during the star/objects-finding process:
The field of view of the telescope or finder scope is different from the direction of the star chart. For example, the view seen through the eyepiece has been flipped, but the observer is not aware that the direction of flipping the star chart or setting the flip direction is incorrect.The observer has set the wrong real field of view obtained by pairing a specific eyepiece with the telescope, making it impossible to match the stars seen in the field of view with the star chart.The position of the target marked on the star chart itself is incorrect.The observer did not confirm the consistency between the direction of the star chart and the field of view of the finder scope before comparing them, resulting in mistaking the default anchor star and going in the wrong direction for the next step.
*個人在鞍部的素描是先以星雲、星系為主，接著做星團的素描，觀測星團的策略相對單純，沒什麼特別之處，高倍率、充分適暗可以得越暗的極限星等。此處11'大小以上的星團除了幾個較大的球狀星團外都是疏散星團(OC)，小的球狀星團使用10公分折射鏡以高倍觀賞星團也輕鬆愜意，使用大口徑則可以拆出更多的星；明亮且大的疏散星團使用小雙筒即可觀賞，小於11'的疏散星團則建議使用八吋徑來觀測。本表中共有39個球狀星團。
*Regarding the sketches made at Anbu, I mainly sketched nebulae and galaxies first, and then did sketches of star clusters. The strategy for observing star clusters is relatively simple, with no particular features. Higher magnification and sufficient darkness can give you a limit magnitude that is fainter. Among the star clusters larger than 11 arcminutes, except for a few larger globular clusters, they are all open clusters (OC). Small globular clusters can be easily observed with a 10 cm refractor at high magnification to enjoy the view comfortably, while using a larger aperture can reveal more stars. Bright and large open clusters can be observed with a small binoculars, while open clusters smaller than 11 arcminutes are recommended to be observed with an 8-inch aperture. There are a total of 39 globular clusters in this table.
*不必過於操心恐懼南方的光害對目視的影響，當然影響是有的，不過如果就333天體的目標來說，星團幾無問題除外，在南方過中天時仰角在四十五度以下的星雲星系，約僅三十個出頭（天爐座星系團以及天蝎尾幾個發射星雲佔去近半），仰角45度以上光害影響和緩許多，據目前觀測狀況估計，在鞍部眼視至少可觀賞三百個以上深空天體。目前畫過鞍部最南可見的星系是半人馬座A星系，仰角21度。
There is no need to worry too much about the impact of light pollution in the south on visual observation at Anbu. Of course, there is an impact, but for the 333 targets of the project, there are hardly any problems with star clusters. Only about 30 or so nebulae and galaxies with an elevation angle below 45 degrees when passing the meridian in the south (with the exception of several emitting nebulae in the Centaurus galaxy cluster and Scorpio's tail) are affected by light pollution. The impact is much less above 45 degrees elevation angle. Based on current observation conditions, it is estimated that at least 300 deep sky objects can be observed visually at Anbu. The southernmost visible galaxy drawn at Anbu so far is the Centaurus A galaxy, with an elevation angle of 21 degrees.
許多人眼視深空天體的印象是 “沒有顏色的一小團模糊的東西似乎沒什麼可看的”
只看見一團模糊的東西、沒有顏色（*），此外就沒有其他的感受，我猜想最大的可能在於只觀看少數幾個特定知名天體，並且只以低倍觀看過，這樣就有可能只因為僅能看到一小團灰灰的，跟看到彩色繽紛的照片完全不一樣，且又僅能看到這幾個天體而感到失望。
但是，如果我們能了解光是不同波長的光子，而顏色是光進入人眼後（並且要夠亮）大腦才會產生的性質（*1）。因為絕大部份的深空天體亮度都過暗，以致於眼視時並沒有顏色，如果我們不執著於人的感官的特質，或許我們可以認為，沒有顏色才是這些天體的「真實」。
建議大家不妨用心體會，當親眼目視，讓穿越時空千里迢迢而來的光子們——小望遠鏡可見的星系的距離至少達千萬光年之遙——直接進入你的視網膜時內心感受的悸動，與欣賞以相機拍攝的照片是無法比擬的，兩種是完全不同的體驗。
同時，使用適當的器材，隨著觀測技巧的精進以及花更長時間的凝視，可以看出越來越多的細節。
Many people's impression of visually observing deep sky objects is "a small, colorless, blurry thing that doesn't seem like there's much to see." Because they only see a fuzzy object without color and have no other feelings. I guess the biggest possibility is that they only observe a few specific well-known celestial bodies and only at low magnification. This may cause disappointment because they can only see a small, grayish object, which is completely different from seeing colorful and vibrant photos, and they can only see these few deep-sky objects. However, if we can understand that color is a property produced by the brain after light enters the human eye (and it needs to be bright enough) and that light is made up of photons of different wavelengths (*1), we can recognize that most deep sky objects are too dim to have color when viewed with the naked eye. If we are not attached to the characteristics of human senses, we may consider that being colorless is the "truth" of these deep-sky objects.
I suggest that everyone try to appreciate the feeling in their hearts when they directly observe the photons that have traveled through time and space for at least tens of millions of light-years, entering their retinas through small telescopes. This feeling cannot be compared to appreciating photos taken with a camera. These are two completely different experiences. At the same time, using appropriate equipment, improving observation skills, and spending more time observing can reveal more and more details.
有一句誤導觀星者很久的了傳言，那便是“觀看深空天體須使用低倍率”
There is a long-standing misconception among stargazers that "you need to use low magnification to observe deep sky objects."
首先，我們應該釐清基本觀念，「低倍」與「大出瞳徑」兩者代表的性質並不同，因為大口徑能夠以更高的倍率得到小口徑低倍相同的出瞳徑，而當出瞳徑相同，兩者視野內的有面積的深空天體（即extended object）的表面亮度也會相同。所以我們應該把適合低倍觀看與適合大出瞳徑觀看分開來討論。
（請注意，當觀測有面積的天體時，我們最在意的是該天體的表面亮度而非視星等，因為視星等是整體積分後的亮度，若另一個天體的視星等雖比前者暗，但面積小很多，若兩者的亮度分佈都很平均，那麼後者的表面亮度有可能比前者亮很多，也就是後者看起來反而比較亮。例如在我已觀測的星系中 NGC 1300 的視星等為10.4，表面亮度只有23.1，另外 NGC 3826的視星等為 9.5，但表面亮度只有22.82 ，相較於前面這兩個星系，NGC 3593 視星等只有 12.6，可是它的表面亮度為20.59，NGC 4474的 視星等為 12.5，表面亮度為20.32，後面這兩個天體視星等比前面兩者來得暗了兩個星等左右，可是表面亮度卻亮了許多，因此更容易辨識出來。 ）
上方星圖裡摸擬的目鏡視野中大圈的是25倍 , 而視野內這群波江、天爐星系其中最大的是 NGC 1365，長徑差不多只有10'左右，核心更小，在筆者眼視素描的近三百個天體中約有高達 190個天體大小在10'以下，這些天體使用25倍以下觀看非常困難或吃力，我們不妨快速的估算一下，即使一個視直徑有10'大小的天體於目鏡中放大25倍約等於有4度視大小，對於一顆70度視野大小的目鏡來說，將近只佔了十七分之一的目鏡的視野直徑（如果視直徑僅5'則將僅為三十五分之一），更何況我們能看見的僅其核心及較亮的部分，通常會比資料上顯示的大小要小許多，譬如球狀星團，透過望遠鏡眼視所見的區域與half_mass 直徑差不多，那通常比星圖上標示的星團大小的一半還要再小。請想像那樣的目鏡中的影像。
觀測這些天體個人主要使用的倍率都在70倍以上（上圖模擬的小圈的視野）。就天體大小來說，以能看到完整的天體輪廓為前提，天體大到僅適合以低倍率觀看的只佔了極少數。在筆者已素描的發射星雲中僅有 14個目標的視直徑是比40'還大，這些即適合以低倍率且大出瞳徑來觀賞；另外有兩個星系以及12個疏散星團大於40'，除了M33星系以外皆非常明亮，大出瞳徑便不是必要的觀測條件。
First of all, we should clarify the basic concept that "low magnification" and "large exit pupil" represent different properties. This is because a large aperture can achieve the same exit pupil as a small aperture at low magnification, and when the exit pupil is the same, the surface brightness of deep sky objects (commonly known as extended objects) in the field of view of both will also be the same. Therefore, we should discuss separately the suitability of low magnification and large exit pupil for observation.
In the star chart above, the larger circle in the eyepiece field of view is at 25x magnification. Among the galaxies in the field of view, including the Pavo and Furnace galaxy groups, the largest is NGC 1365, with a diameter of only about 10 arcminutes and an even smaller core. Among nearly 300 deep-sky objects sketched by the author, as many as 190 objects are smaller than 10 arcminutes in size. It is very difficult or strenuous to observe these objects at magnifications below 25x. Let's do a quick calculation. Even if a DSO with a visual diameter of 10 arcminutes is magnified 25 times in an eyepiece, it is only about 4 degrees in visual size. For an eyepiece with a 70-degree field of view, it only occupies about one seventeenth of the eyepiece's visual diameter (if the visual diameter is only 5 arcminutes, it will be only one thirty-fifth). Moreover, what we can see is only its core and brighter parts, which are usually much smaller than the size shown in the data. For example, a globular cluster seen through a telescope has an area that is about half of the size indicated on a star chart. Please imagine what the image in such an eyepiece looks like.
Personally, I use magnifications of 70x or higher to observe these objects (the smaller circle in the simulated field of view in the figure above). In terms of celestial body size, only a very small number are so large that they are only suitable for low magnification observation. The premise is to be able to see the complete outline of the deep-sky object. Among the emission nebulae sketched by the author, only 14 targets have a visual diameter larger than 40 arcminutes, which are suitable for observation with low magnification and large exit pupil. In addition, two galaxies and 12 open clusters are larger than 40 arcminutes. Except for the M33 galaxy, they are all very bright and do not require large exit pupils for observation.
天體大小統計 （紅字為已進行眼視素描 2022/09/01）
如果不考慮天體放大後是否會大於目鏡視野，以高倍觀賞的優勢首先在於，能得到越暗的極限星等，這是觀測星團的成員星所需要的。
此外，當使用相同出瞳徑下人眼對於視面積較大的影像的辨識所需的天體與背景天空的亮度對比門檻會較低(*2)。 換言之，當天空亮度與天體亮度對比固定不變時，面積越大越容易辨識（但須避免放大到天體本身的表面亮度過低）。
If we don't consider whether the deep-sky object will be larger than the eyepiece field of view after magnification, the advantage of observing at high magnification is that we can obtain a fainter limiting magnitude, which is necessary for observing the member stars of star clusters.
In addition, when using the same exit pupil, the threshold of brightness contrast between extended objects and the background sky that the human eye needs to recognize larger images will be lower (*2). In other words, when the contrast between the sky brightness and the celestial object brightness remains constant, larger objects are easier to recognize (but avoid magnifying to the point where the surface brightness of the extended object itself becomes too low).
上圖為筆者的三百個深空天體觀測中的有面積天體（星系、星雲、球狀星團）的實際觀測數據統計（圖表上方乃天體表面亮度較天空為暗），足以驗證Blackkwell 於1946年所做的關於人眼對比門檻的實驗，即越黯淡的東西在越大的視面積下越容易看見(*2)。
The above figure shows the actual observation data statistics of extended objects (galaxies, nebulae, globular clusters) among the 300 deep sky objects observed by the author (the surface brightness of the objects is darker than the sky above the chart), which is sufficient to verify Blackwell's experiment in 1946 on the contrast threshold of the human eye, that is, dimmer things are easier to see with larger visual areas (*2).
此外，在大口徑、高倍下的眼視的視覺經驗的豐富性又是僅以低倍 (這裡指25x 以下) 逡巡下無法感受到的，兩者是完全不同的世界（適合不同的目的，低倍大視野雖有其壯闊之美，但不能期望看出多少細節），有機會請務必試著以高倍觀賞，若亮度不足就加大口徑來得到大出瞳徑，如此，即使以8"以內的小型望遠鏡也能得到不少的趣味。
例如，獵戶座大星雲使用8"觀看，50倍左右可以看到羽翼邊緣的輪廓，而四合星一帶在 300x的高倍目視下就彷彿從航行中的太空船的窗戶向外眺望般身歷其境，雲氣非常的濃密立體，即高倍可以看到更多細節。
In addition, the richness of visual experience at high magnification and large aperture is something that cannot be felt by only cruising at low magnification (here referring to below 25x), and the two are completely different worlds (suitable for different purposes. Although low magnification and large field of view have their grandeur, one cannot expect to see much detail). If you have the opportunity, please try observing at high magnification. If the brightness is insufficient, increase the aperture to obtain a larger exit pupil. In this way, even with a small telescope of less than 8 inches, you can still get a lot of fun.
For example, when observing the Orion Nebula with an 8-inch telescope at around 50x magnification, you can see the outline of the wings. And in the area around the Trapezium Cluster, at a high magnification of 300x, it is like looking out of a window of a spaceship in flight, with very dense and three-dimensional clouds, which shows that high magnification can reveal more details.
M63向日葵星系在8" 200x 左右的目視下可以看見旋臂的一些不均勻的光斑如發出微光的魚鱗，那也像是花瓣，非常美麗，是我最愛的天體之一。
The M63 Sunflower Galaxy can be seen at around 200x magnification with an 8-inch telescope, and some uneven patches of light on the spiral arms can be seen, like scales emitting faint light, or like petals. It is very beautiful and is one of my favorite celestial objects.
M6蝴蝶星團以10公分口徑 30～70倍觀看時，一顆顆顆明亮的星子如同從以釘子鑿出蝴蝶圖案的奶粉罐燈籠透出來的燭光。而巨大的球狀星團諸如M13, M15, NGC5139 Omega 等以10公分, 80倍以上觀看即非常震撼。此外，只要天空表面暗度達到20左右，使用6"牛頓 25倍左右觀賞面紗星雲就非常明亮，亮到可以深刻感覺到星雲“正在發着光”，也可看到一點絲狀結構，10公分口徑也可見面紗，以OIII濾鏡輔助對比更高。
在深邃幽暗的宇宙之海中的鯨魚星系 NGC4631，以8" 50倍左右身形就非常明顯龐大，在黑暗中悠游有種特別的神祕感。M33星系以 8" 鏡40~50倍左右則可以看到旋臂。土星狀星雲相當亮且亮度集中於很小面積（視大小長徑僅41"左右），以8" 放大到600倍，視野約5' 仍明顯可見。較低倍率下可見其呈現藍綠色光芒，口徑越大則越高倍率仍可見顏色。（S=15.74 MPSAS 在40倍、出曈徑約 5mm以下之亮度仍是理論上負責顏色的cone細胞可以運作的亮度 0.03 cd/m^2, 約16.4 MPSAS）。
NGC7293螺旋星雲以8" 鏡50倍左右加上LP2(OIII+H-beta）的輔助下即使天空表面亮度只有19.5不到，星雲也像是蹦出來般非常立體，跟觀看天琴座 M57甜甜圈星雲（M57使用5公分口徑也看得到）的立體感很像。
When observing the Butterfly Cluster M6 at 30-70x magnification with a 10cm aperture, the bright stars look like candlelight shining through the holes of a milk can lantern carved with butterfly patterns. Giant globular clusters such as M13, M15, NGC5139 Omega, etc. are very impressive when observed at 80x magnification or more with a 10cm aperture.
In addition, if the sky surface brightness reaches around 20, observing the Veil Nebula with a 6-inch Newtonian telescope at around 25x magnification is very bright, and you can deeply feel that the nebula "is emitting light." You can also see some filamentous structures. The Veil Nebula is also visible with a 10cm aperture, and the use of an OIII filter can enhance the contrast.
In the deep and dark ocean of the universe, the Whale Galaxy NGC4631 is very large and conspicuous at around 50x magnification with an 8-inch telescope, giving a special sense of mystery in the darkness. The spiral arms of the M33 galaxy can be seen at around 40-50x magnification with an 8-inch telescope.
The Saturn Nebula is quite bright and concentrated in a small area (with an apparent size of only about 41"), and can still be clearly seen when magnified to 600x with an 8-inch telescope and a field of view of about 5'. At lower magnifications, it appears blue-green in color, and larger apertures can reveal more details and colors. (S=15.74 MPSAS, at 40x magnification and an exit pupil of about 5mm or less, the brightness is still within the theoretical range where cone cells responsible for color vision can function, at 0.03 cd/m^2, approximately 16.4 MPSAS).
With the assistance of an LP2 filter (OIII+H-beta), even if the sky surface brightness is less than 19.5, the Helix Nebula NGC7293 looks very three-dimensional at around 50x magnification with an 8-inch telescope, as if it is popping out, similar to the three-dimensional feeling when observing the Ring Nebula M57 in Lyra (which can be seen even with a 5cm aperture).
高倍觀測的重點之一在於口徑，口徑越大便能以更高的倍率得到同樣的出瞳徑（出瞳徑等於口徑除以倍率），而同樣的出瞳徑的目鏡視野中天體的表面亮度是一樣的。
One of the key points of high magnification observation is aperture. With a larger aperture, you can achieve the same exit pupil (exit pupil equals aperture divided by magnification) at a higher magnification. And for the same exit pupil, the surface brightness of extended objects in the eyepiece field of view is the same.
另一個迷思是：從望遠鏡內看到的天體會比裸眼更亮？集光力比越大的望遠鏡會使得目鏡內的天體越亮？
Another misconception is: Are celestial objects seen through a telescope brighter than with the naked eye? Does a telescope with a larger light-gathering power make celestial objects in the eyepiece brighter?
這句話只對了一半。因為這句話只適用於點光源。對於有面積的天體來說，因為倍率放大為2倍，光線就被擴散到了原來的四倍面積，如果我們以7mm的人眼瞳孔去計算，會發現當望遠鏡出瞳徑為7mm時，剛好集光力的倍數會等於光線被擴散的倍數，因此望遠鏡中的天體表面亮度仍然等於裸眼時的天體表面亮度。
因此，當望遠鏡搭配目鏡能得出 7mm的超大出瞳徑時（這時放大了的視野內天體與天空的表面亮度皆與放大前一致並沒有改變，即裸眼所見的表面亮度），這也是我們能得到的天體的最亮的表面亮度了，倍率再高天體表面亮度（以及天空表面亮度）就會開始變暗了。而當再拉高倍率天空表面亮度變暗，我們就可以看到比裸眼能見的更暗星等的恆星（點光源）。
This statement is only half correct. It only applies to point sources of light. For extended objects, when the magnification is doubled, the light is spread over four times the area. If we calculate based on a 7mm human pupil, we will find that when the telescope exit pupil is 7mm, the light gathering power is equal to the amount of spreading of the light. Therefore, the surface brightness of objects in the telescope is still equal to that seen with the naked eye.
Therefore, when a telescope with an eyepiece that achieves a large exit pupil of 7mm (where the surface brightness of extended objects and the sky remains the same as before magnification), this is the brightest surface brightness we can obtain from the objects. Any further increase in magnification will cause the surface brightness (and sky surface brightness) to decrease. When the magnification is further increased and the sky surface brightness decreases, we can see stars with fainter apparent magnitudes (point sources) than what can be seen with the naked eye.
接著來討論必須使用大出瞳徑觀賞的深空天體。
適合超大出瞳徑觀測的這些天體乃是表面亮度極低的困難目標，只要出瞳徑縮小一些都可能讓它們變得過暗而無法辨識，這幾個困難目標幾乎都是HII 區的發射星雲（及極少數反射星雲）。
個人以ASTROTRACER 的短曝調查的約350個天體表中大於 10'的星雲有59個，其中只有NGC7293螺旋星雲是行星狀星雲，而在這58個發射星雲之中目前尚未進行眼視或初次眼視未看見的目標有34個，多是IC（NGC的補充）或 Sharpless（HII區巡天）這些非常黯淡的由攝影編撰的天體目錄中的目標，這幾個發射星雲便是筆者提到的困難目標（前面統計中的粉紅色天體），如果放大降低對比門檻並無法看到，個人認為即適合等待透明極佳的深夜以最大極限出瞳徑7mm，以及搭配OAKs LP2濾鏡（或僅Hb）來嘗試挑戰郊山深空觀測的極限（需注意人的瞳孔張到最大時的直徑會隨年齡越大而減小，出瞳徑比瞳孔大會浪費光線，所以比7mm大的出瞳徑並無效果）。這裡要提醒一下，這34個目標經個人長曝調查其中有至少20個是即使以OIII濾鏡（接近人眼桿狀細胞最敏感的波段中心）曝光十分鐘仍看不見或幾乎看不見影像的 (*3)，這些天體對眼視來說本就非常困難。
Next, let's discuss deep sky objects that require a large exit pupil to observe.
These objects are difficult targets with extremely low surface brightness. Even a slight reduction in exit pupil size can make them too dim to identify. Almost all of these difficult targets are HII region emission nebulae (and a very small number of reflection nebulae).
Out of approximately 350 objects in my personal short exposure survey using ASTROTRACER, there are 59 nebulae larger than 10'. Among them, only the NGC 7293 Helix Nebula is a planetary nebula. Of the remaining 58 emission nebulae, there are currently 34 targets that have not been seen visually or have not been seen in the first visual observation. These are mostly targets from catalogs of very faint objects compiled from photography, such as IC (supplementary to NGC) or Sharpless (HII region survey). These emission nebulae are the difficult targets mentioned earlier (pink objects in the previous statistics). If magnification is increased and contrast threshold is lowered but still cannot be seen, I believe it is suitable to wait for an extremely clear night and use the maximum exit pupil of 7mm, along with the OAKs LP2 filter (or only Hb), to attempt to challenge the limits of suburban deep sky observation (note that the maximum diameter of the human pupil decreases with age, and an exit pupil larger than the pupil size will waste light, so an exit pupil larger than 7mm is ineffective). It should be noted that out of these 34 targets, at least 20 were identified in my personal long exposure survey as being very difficult to see even after being exposed for ten minutes with an OIII filter (which is close to the center of the wavelength range most sensitive to human rod cells), making these objects very challenging for visual observation.
必需讓眼睛「達到並維持」在充分適應黑暗的狀態才能看得到極限星等，這點經常被觀星者忽略
NGC6939 與 NGC6946很適合用來測試、證明 適暗性(Dark adaptation) 以及 倍率的重要性。特別是 NGC6939這個 10'大小的疏散星團，以下面的素描的例子，雖使用紅光，若素描時照明太強，即使無直接照射眼睛，觀看反射的光線之後的兩、三分鐘內，也連12等星都看不到（一開始目鏡視野內是全黑，視覺的變化類似就寢關燈後所見），等到眼睛的視桿細胞適暗充分之後（約至少二十分鐘以上，這也是之所以需選擇沒有路燈照明或來往車燈干擾的觀測地，否則每次干擾後都要等待眼睛重建適暗性），極限星等達到約12.9 等 (*4)。
以素描當晚的天空暗度，Pentax 105SDHF在 233倍下理論計算的極限星等估算約可達到 13.2~13.4等（實際觀測的極限星等是 12.9等，主要可能是受透明度影響），若僅以23倍觀察則極限星等約僅有 11.2～11.5等。P105 在233倍下出瞳徑 0.45mm，這出瞳徑應該差不多是我的極限了，很暗，為了維持較佳的適暗性這個小疏散星團的素描我就無法採取邊照明邊素描的方式，而是在完全不使用照明，眼睛不移開目鏡視野下憑感覺摸黑在紙上抓距離一口氣先畫上所有能看到的星點，然後再比照星圖，結果發現可見恆星與其相對位置都差不多，可見不是雜訊。這個星團的恆星只有一顆比12等亮的（TYC 4233-2452-1 ，+11.4)，所以不使用高倍是無法看出這裡有一個星團的。
To see the limit magnitude, it is necessary to "reach and maintain" a fully dark adaptation , which is often overlooked by stargazers.
NGC 6939 and NGC 6946 are very suitable for testing and demonstrating the importance of dark adaptation and magnification. In particular, NGC 6939, a 10' open cluster, is an example. Even with red light used during sketching, if the illumination is too strong, even if the eyes are not directly exposed, for the following two to three minutes after viewing the reflected light, stars as faint as magnitude 12 cannot be seen (at the beginning, the entire field of view is black, and the visual change is similar to what is seen after turning off the lights before going to bed). After the rod cells in the eyes have fully adapted to the dark (at least 20 minutes or more), the limit magnitude reaches about 12.9 (x4). This is why it is necessary to choose an observation site without streetlights or passing car lights that can interfere with dark adaptation. Otherwise, after each interference, you have to wait for your eyes to rebuild dark adaptation.
Based on the sky darkness on the night of the sketch, the theoretical limit magnitude estimated for the Pentax 105SDHF at 233x is about 13.2-13.4 (the actual observed limit magnitude was 12.9, mainly due to transparency). If observed at only 23x, the limit magnitude is only about 11.2-11.5. The exit pupil of P105 at 233x is 0.45mm, which should be close to my limit. It is very dark. In order to maintain better dark adaptation, I could not use side lighting while sketching this small open cluster. Instead, I had to feel my way in the dark without moving my eyes away from the field of view and draw all visible stars on paper at once. Then, I compared it with a star chart and found that the visible stars and their relative positions were almost identical, indicating that they were not noise. The stars in this cluster are all fainter than magnitude 12, except for one (TYC 4233-2452-1, +11.4), so it is impossible to see this cluster without high magnification.
19個小行星狀星雲
在筆者的大屯鞍部300個素描天體大小統計中，您會發現小於1'天體的星系與星團數量皆為0，這並非指沒有視直徑小於一角分（一弧分）的星團星系，而是因為筆者在一開始選擇、建立觀賞目標清單時便已經把這些天體排除，因為對小型望遠鏡來說在bortle 5的光害下這些天體實在非常小又暗。然則素描中卻有17個小於1'的星雲 (2022/09/01 視大小在1'以下的新增為24個)，乃是因為這些星雲絕大多數皆非常亮。是的，沒有意外，這十七個小星雲都是行星狀星雲 (*5)。
由於這些行星狀星雲的亮度集中在非常小的面積，所以它們的表面亮度皆相當亮，且因為絕大多數行星狀星雲發出的光線最強的波長為OIII (501nm), 正接近視桿細胞視覺最敏銳的波段中心，所以對於眼視觀賞非常有利。當夠亮看得出顏色時它的顏色會呈綠色或藍綠色（視不同的觀察者的視覺可能會有差異）。
再加上羅盤座 NGC2818與天琴座 M57 環狀星雲另外兩個大小也差不多的行星狀星雲，一共十九個小行星狀星雲，以各種小型望遠鏡皆適合觀賞它們（個人素描從3"到8"鏡都有使用），如果想要嘗試看見星雲的顏色，那麼這19個行星狀星雲就是最好的目標了。
總言之，眼視有觀看照片無法取代的感受與樂趣，你也許會對自己拍過的M57彩色影像印象不深，拍過後一段時間就忘了，然則你絕對不會忘記你第一次以高倍 (80x上下)觀看M57時的感受，即使在數年後。
有機會請務必嘗試眼視，並且嘗試高倍的觀賞。
There are 19 planetary nebulae in total. In my statistical study of 300 sketched objects in Datun-Anbu, you will find that the number of galaxies and star clusters smaller than 1' is 0. This does not mean that there are no star clusters or galaxies with an angular diameter less than one arcminute, but because I excluded these objects when I initially chose and created the observation target list. This is because these objects are very small and dim under Bortle 5 light pollution for small telescopes. However, there are 17 planetary nebulae smaller than 1' in my sketches (as of 2022/09/01, there are 24 newly added objects smaller than 1'). Most of these planetary nebulae are very bright. Yes, without exception, these 17 small planetary nebulae are all planetary nebulae (*5).
Since the brightness of these planetary nebulae is concentrated in a very small area, their surface brightness is quite bright. Moreover, since the strongest wavelength of light emitted by most planetary nebulae is OIII (501nm), which is close to the center of the wavelength band where rod cells in the eyes are most sensitive, it is very advantageous for visual observation. When bright enough to see the color, its color will be green or blue-green (depending on the observer's vision).
Together with NGC2818 in Lupus and M57 in Lyra, two other planetary nebulae of similar size, there are a total of 19 small planetary nebulae that can be observed with various small telescopes (my sketches range from 3" to 8" mirrors). If you want to try to see the color of the nebula, then these 19 planetary nebulae are the best targets.
In summary, visual observation provides a feeling and pleasure that cannot be replaced by photographs. You may not have a strong impression of the color image of M57 that you took yourself, and you may forget it after a while. However, you will never forget the feeling when you first observed M57 at high magnification (around 80x), even after several years. If you have the opportunity, please try visual observation and try high magnification observation.
*1 人眼的構造中負責亮視覺的視椎細胞有三種，能接收三個不同波段的光線，而人腦不知怎地就能把這些細胞接受的光變成色彩，然則負責暗視覺的視桿細胞只有一種，且人腦無法由視桿細胞產生顏色，因此過暗的事物對我們來說便沒有顏色。
*2 請參考Blackwell 1946年的人眼辨識對比門檻實驗 Contrast Thresholds of the Human Eye 一 H. Richard Blackwell 1946
*3 這二十個星雲為： NGC1333（反射星雲+發射星雲）, NGC1499, IC59, IC63（反射星雲+發射星雲）, IC405（反射星雲+發射星雲）, IC417, IC434, IC1283, IC1284, IC4604, IC4605（複合星雲） ，IC5146, sh2-9(反射星雲+發射星雲), sh2-13, sh2-16, sh2-54, sh2-155, sh2-157, sh2-276, sh2-240。可以大膽假設這些發射星雲的Hb發射線要比[OIII]強。
*4 這也是當導覽者欲分享已在目鏡視野中的目標給一旁的同好觀賞時，而旁人有時會無法如願看見的因素之一，並非是他們的視力不好，而是他們的眼睛事實上仍未進入完全適暗的狀態，不要想在眼睛湊近目鏡的頭一兩分鐘內就能看見目標，實際上需要的是更長的凝視。
*5 這些行星狀星雲分別是：鹿豹座NGC1501, 仙王座NGC40, 波江座NGC1535 埃及豔后的眼睛，雙子座NGC2392 愛斯基摩人星雲，船帆座NGC3132 南環狀星雲，長蛇座NGC3242 土星的鬼魂或眼睛星雲，天蠍座NGC6302 蟲子星雲，人馬座NGC6445 新月星雲，天龍座NGC6543 貓眼星雲，蛇夫座NGC6572，人馬座NGC6818 小寶石星雲，海豚座NGC6905 藍色閃光星雲，水瓶座NGC7009 土星星雲，天鵝座NGC7027，仙女座NGC7662 藍雪球星雲，烏鴉座NGC4361, 船尾座NGC2440。當倍率在300x以下比較難觀察這些小行星狀星雲的輪廓。
倍率放大降低的背景表面亮度(MPSAS) △S.B.(mpsas)= 5 log10 (倍率 /（0.1116 × 望遠鏡口徑mm))
考慮倍率放大後的望遠鏡極限星等＝觀測時的裸眼極限星等 + 5 log10 (口徑· √T / 觀測者瞳孔徑)+ 2 log10 (觀測者瞳孔徑 / 望遠鏡出瞳徑)
＊註：劃線部份是望遠鏡極限星等規格的計算公式(代入理想值就是標稱的規格)，未劃線部份是倍率的效果；口徑 / 觀測者瞳孔徑 ＝該望遠鏡的最低有效倍率；T =Transmission 系統的光傳輸係數 （公式請參考www.telescope-optics.net）。以下連結為納入了各種因素的計算器。
出瞳徑不適合太小，天體可能會過暗，反之若大於瞳孔直徑則會浪費光線（但不一定會影響觀測），不滿二十歲的青少年的瞳孔差不多有7mm大，一般望遠鏡的最小倍率即是以7mm出瞳徑去計算。隨著年紀漸大瞳孔會逐漸縮小，到了五十歲時瞳孔大小可能只剩5~6 mm。
目鏡規格標示的視視野也就是我們望進目鏡中會看到的影像大小（視角）。而因為目鏡焦距是已知，從搭配的望遠鏡焦距我們可求得 倍率(=物鏡焦距/目鏡焦距)，我們於是可知道這個目鏡的成像影像是從多少的天空大小（實視野）放大成的。
實視野的另一種計算方式是利用目鏡的場欄(field stop)來估算，計算方法為 場欄/望遠鏡焦長*57.3。一般而言1.25" 目鏡場欄最大為27mm, 2"目鏡則是46mm, 這限制了望遠鏡所能得到的最大實視野。
望遠鏡搭配目鏡再加上眼睛才能成像。這個物鏡加上目鏡的系統就叫AFOCAL，從目鏡射出的光線是平行的，需再經由眼睛聚焦至視網膜上成像。運用在攝影上則是在目鏡後端加上含鏡頭的攝影裝置，稱作AFocal Imaging（請參考小折射鏡多功能化），由於目鏡在這裡作用相當為一個準直鏡（讓出去的光線為平行光），所以又叫做準直法攝影。
倍率放大時，extended objects （有面積的天體，即大於角解析力的天體）與背景視野一起放大，故對比（亮度差距）不變，但人眼可辨識出天體的對比門檻則會隨天體面積增大而降低，所以理論上是可以一直放大到觀測者覺得出瞳徑已經過小。(但放大至某倍率之後亮度降低的速度反而會比對比門檻的降低還快，我們可以將這個倍率作為是觀看該天體的最佳倍率的參考。)
When magnifying, extended objects (celestial objects with an area larger than the angular resolution) and the background field of view are magnified together, so the contrast (brightness difference) remains the same. However, the contrast threshold for recognizing objects by the human eye will decrease as the size of the extended object increases. Therefore, in theory, it is possible to keep magnifying until the observer feels that the exit pupil is too small. (However, after magnifying to a certain magnification, the rate of brightness decrease will be faster than the decrease of the contrast threshold. We can use this magnification as a reference for the optimal magnification for observing that celestial object.)
＊亮度較均勻擴散的星系或星雲，我們通常可以利用天體的表面亮度（如果已有可靠的表面亮度數據）與觀測當時的天空表面亮度來評估為達到此對比的辨識門檻所需的放大後的天體面積大小（放大倍率），若你的望遠鏡放大到此倍率時已太暗，則可以從此倍率與適切的出瞳徑（足夠的光量，譬如個人覺得出瞳徑 2.5mm以上就已經算相當舒適，1mm以下除非觀察行星或極為明亮的深空天體，或為了觀察更細節的微小處而為之，0.5mm差不多是極限）來考慮合適的口徑。
＊關於有面積天體的目視對比門檻請參考RASC 觀測手冊，原理為：若以同樣的對比（同樣的天空表面亮度，同樣的天體表面亮度）為比較基礎，則視野中的天體面積越大則越容易被辨識出。於個人的333 objects Excel表格中，可以查到一些天體的表面亮度 S.B. 值 。因為正好有M97貓頭鷹星雲的表面亮度（ ＝21.6 mpsas），所以我們就以前面提到的例子說明如下（不加任何濾鏡的情況）：
當 Pentax 75SDHF使用20mm目鏡時為25倍，出瞳徑乃 75/25=3 ，查表得目鏡視野中的天空與天體的表面亮度會由原表面亮度各降 1.8 mpsas亮度，當時天空的表面亮度測為 20.02 mpsas ，故放大倍率後的視野裡的天空背景亮度為 21.82，視野裡的Ｍ97表面亮度為 21.6+1.8=23.4。
以 M97 於視野中的大小為 3’ x 25 = 75’ 與天空背景亮度21.82 查表1，經內插查得可辨識的天體的表面亮度門檻約為 23.15，但此刻視野中的M97表面乃23.4比此門檻還暗（但在誤差範圍內），故不太容易辨識。
現在我們若改用Mewlon 210，在同樣的天空亮度下，若用同樣的 3mm 出瞳徑，也就是使用倍率 210/3= 70x （約搭35mm目鏡可得），視野中的天空背景亮度將是同樣的 21.82, 視野中的M97表面亮度也是 23.4，唯一不同的是現在視野中的M97大小是 3.3’ x 70 =231’ ，查表1 內插得到的視野中的天體表面亮度辨識門檻變為 24.23，因此刻視野中的M97 比門檻亮上許多可以輕易被辨識出。（當然，這僅供參考，尚有觀測者本身經驗因素也有影響，或者天體本身亮度並不均勻，譬如星系若有明亮核心，那麼就會比用表面亮度來估算的易見許多。
若我們用另一種敘述方式來解釋上面的結果，以RASC的定義天體與天空表面亮度差為對比，那麼上面的25倍與70倍的對比都是一樣的21.6-20.02=1.58（不同放大率並不會改變這個對比,因為天體與天空總會減掉同樣亮度），但是在25倍時眼睛無法辨識出1.58的對比，而在70倍時卻可以辨識出，所以此處我們也可以用Clark的研究這樣解釋「更大的天體視面積即更高的倍率降低了眼睛可辨識的對比門檻」。（以上計算亦可以藉由RASC 提供的Magnitude and Contrast Calculator 試算表 求出）
*For galaxies or nebulae with relatively uniform and diffuse brightness, we can evaluate the required magnification (magnification factor) to achieve the desired contrast threshold for recognition by comparing the surface brightness of the celestial object (if reliable surface brightness data is available) with the sky surface brightness at the time of observation. If the target becomes too dim when the telescope is magnified to this factor, we can consider an appropriate aperture based on this magnification and an appropriate exit pupil (sufficient light, for example, a personal comfort level would be an exit pupil of 2.5mm or larger, unless observing planets or extremely bright deep sky objects, or for the purpose of observing finer details in small areas, where 0.5mm would be the limit).
*Regarding the visual contrast threshold for extended objects, please refer to the RASC Observing Handbook. The principle is as follows: if the same contrast (the same sky surface brightness and celestial object surface brightness) is used as a basis for comparison, the larger the area of the extended object in the field of view, the easier it is to recognize. In my personal 333 objects Excel spreadsheet, you can find some surface brightness (S.B.) values for certain objects. Since we happen to have the surface brightness of the M97 Owl Nebula (S.B. = 21.6 mpsas), let's use the example mentioned earlier (without using any filters):
When using a 20mm eyepiece on the Pentax 75SDHF, the magnification is 25x, and the exit pupil is 75/25 = 3mm. According to the table, the sky and object surface brightness in the eyepiece's field of view would decrease by 1.8 mpsas. If the sky's surface brightness at the time is measured to be 20.02 mpsas, the background brightness in the magnified field of view would be 21.82, and the M97's surface brightness in the field of view would be 21.6 + 1.8 = 23.4.
With M97 measuring 3' in the field of view and a sky background brightness of 21.82 (according to Table 1), an interpolated value indicates a threshold surface brightness for recognizable objects of approximately 23.15. However, the M97's surface brightness in the field of view at that moment is 23.4, slightly dimmer than the threshold (within the margin of error), making it less easily recognizable.
Now, if we use the Mewlon 210, under the same sky brightness, with the same 3mm exit pupil (approximately using a 35mm eyepiece), the background brightness in the field of view would still be 21.82, and the M97's surface brightness in the field of view would still be 23.4. The only difference is that the size of M97 in the field of view is now 3.3' x 70 = 231', and based on Table 1, the threshold for recognizable celestial object surface brightness in the field of view becomes 24.23. Thus, the M97 in the field of view is much brighter than the threshold and can be easily recognized. (Of course, this is for reference only, as the observer's experience and the uneven brightness of the object itself can also have an impact. For example, if a galaxy has a bright core, it will be much more visible than estimated based on surface brightness.)
If we describe the results using a different approach, according to the RASC's definition of contrast as the difference in surface brightness between the extended object and the sky, both the 25x and 70x magnifications have the same contrast of 21.6 - 20.02 = 1.58 (different magnifications do not change this contrast, as the celestial object and the sky will always subtract the same brightness). However, at 25x magnification, the human eye cannot distinguish the 1.58 contrast, while at 70x magnification, it can be recognized. Therefore, we can also explain that "larger celestial object surface area or higher magnification reduces the contrast threshold discernible by the human eye" using Clark's research. (These calculations can also be performed using the Magnitude and Contrast Calculator provided by RASC.)
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這跟放大倍率以及目鏡的規格的視視野有關。我們這裡以視視野六十度的目鏡來舉例，如果以下圖中的iPad mini來播放照片，當我們把照片放大到iPad mini的螢幕框大小時，影像長大約是15cm，利用三角函數我們可以得到眼睛從距離螢幕大約13公分的地方看照片差不多就是視視野60度的感覺。（這裡只是示範，請注意眼睛務必與離螢幕保持適當距離，最好是列印在紙上來做實驗。）
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人眼在進入黑暗中約經三十分鐘後能達到比白天高一萬倍以上的暗處細節的辨識能力，又因為人眼在黑暗中作用的視杆細胞感應波長峰值約在498nm，對紅光則不敏感，所以建議需要照明時使用低強度紅光的頭燈，可避免破壞自己（或他人）好不容易建立好的眼睛適暗性。
When the human eye looks at light and then looks at the dark sky, at first, only objects that are relatively bright and processed by cone cells can be seen. After a few minutes, rod cells begin to gradually take effect (sensitivity increases, the duration depends on the intensity of light that stimulated the eye before, the stronger the light received, the longer it takes to reach this threshold), and objects with a brightness less than 0.03 cd/m² (approximately 16.4 mag/arcsec², below which cone cells responsible for brightness vision and color perception lose their function) can be seen. Because it takes about thirty minutes to fully adapt to darkness (rod cells' sensitivity can reach 10^-5 cd/m²), and if there is continuous light interference, it will never fully adapt to darkness.
After about thirty minutes in the dark, the human eye can achieve a recognition ability for details in darkness that is over ten thousand times higher than during the day. Additionally, because the peak wavelength sensitivity of rod cells in the human eye is about 498nm in darkness, it is not sensitive to red light. Therefore, it is recommended to use a low-intensity red light headlamp when illumination is needed to avoid destroying one's (or others') dark adaptation that has been painstakingly established.
眼視用窄頻濾鏡
在鞍部觀賞發射星雲使用濾鏡個人建議應包含Hb波段。詳見 發射星雲概觀 一文。
目鏡視野參考：
Mewlon 210
可以設定 模擬目鏡視野的電子星圖對觀測幫助很大，如果目鏡廠商的規格正確，據個人 用準直拍攝實測， skysafari pro的模式視野大小與實際眼視所見相當吻合。
Most spectacular deep sky objects for visual observing at Yangmingshan. skylist
這是從331清單再選出其中我覺得特別精彩的眼視目標，如果是在八月底左右從入夜後觀測到黎明，則應該除了春天的星系大道那條路線上的星系(M81,M82以下)其他都依序可看見。
原來你的計畫這麼詳細，受教了。
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