草山星空: 眼視距離我們有24億光年之遙的 3C 273類星體 (目前是郊山以肉眼透過8"小望遠鏡所能見到的最遠天體) ／鞍部夏季銀河與處理備忘

Visual observation of 3C 273/ Summer Milky Way above Anbu and image processing notes.

The 3C 273 quasar, located at a distance of 2.4 billion light-years from us (currently the farthest celestial object visible to the naked eye through an 8-inch telescope in suburban areas)

(updated 07/18 文末影片：以Siril對彩色相機的RAW檔做快速簡易背景校正並加強對比處理的步驟。 Background extraction of one-shot color RAW file via siril；以及以Registar 做馬賽克疊合。)

7/9 晚

鞍部的夏季銀河 Summer milky way above Datun Anbu, Yangmingshan

Pentax K5 (full spectrum mod.), Red Enhancer filter, ir-cut filter , Samyang 16/F2, ISO1600, ASTROTRACER 40sec x30（各區分別先拍攝數張，每張都先以Siril做背景校正，然後以Registar對齊、校色、疊合（分南北兩段），最後以Photomerge 接合兩段並校正變形）

鞍部的夏季銀河全景 Summer Milky Way above Anbu（ASTROTRACER 40sec x 42）。

到山上時許久不見的Andy已經架好赤道儀在拍攝深空了。

今晚只帶相機腳架，打算馬賽克拍攝帶地景的鞍部夏季銀河，也想如接鞍部秋季銀河拱形全景那張也好好來接一次夏季銀河拱形，不過夏季銀河的跨度較大，所以如果想要萬無一失要分更多區來接起來，因為沒有特地用分度雲台，只大概抓一下重疊區，不敢大意所以拍了二十幾個區塊（連地景也重複了好幾張），再花時間慢慢處理。

今晚在山上遇到一位新的星友，一起在一旁架著腳架拍著銀河。此外有幾位某校來看星空的學生，看到滿天星星非常興奮，拿著手機拍著星空，我跟他們說了現在銀河升上來了喔，告訴他們銀河的方位。手機使用的感光元件也同樣隨著相機在進步中，在這裡只要能長曝都能夠曝出銀河。

I arrived at the mountain and saw Andy, whom I haven't seen in a long time, already set up an equatorial mount to shoot deep space.

I only brought a camera tripod tonight, planning to shoot a mosaic of the Anbu summer Milky Way with landscape. I also wanted to shoot the summer Milky Way arch once again, as in the Anbu autumn Milky Way arch panoramic. However, the summer Milky Way is wider, so if you want to be foolproof, you need to divide it into more areas to connect. Because I didn't use a differential mount specifically, I could only roughly grasp the overlapping area. I didn't dare to be careless, so I shot twenty or so blocks (including the landscape, each block shot a few shots), and then spent time slowly processing.

Tonight on the mountain, I met a new astronomy lover, and we set up tripods next to each other to shoot the Milky Way. In addition, there were a few students from a certain school to see the starry sky. They saw the full sky of stars very excited, holding their mobile phones to shoot the starry sky. I told them that the Milky Way has come up, and told them the location of the Milky Way. The sensor used in the mobile phone also improves with the development of the camera, and here, as long as it can be long-exposed, it can be exposed to the Milky Way.

＊＊＊

7/8 晚 ~7/9 凌晨

金星這幾天正逢最大亮度期，今晚的暮色也很美，在上山的途中忍不住停下來拍一張。

因為計畫要看3C273，所以今晚帶高橋的 Mewlon 210上來。

今晚月相約65％，不到午夜約十一點左右即會升上來（在鞍部東側有上小觀音山的稜線擋住，大約可觀測至十二時，月光影響仍不大），所以只打算觀測上半夜，又因為3C273位在室女座，是春天的星座，目前入夜後已在西側仰角不高，必需搶在它西沈入大屯山前觀測，所以今晚特地在暮光尚未結束時就到停車來架設赤道儀，大約八點半之後即開始觀測。

天文暮光方盡，但夜空離達到最暗的午夜尚早，不過透明度很不錯，所以雖然西方仰角三十度左右的天空表面亮度仍未達19，仍然在7x50 的尋星鏡內可以依序找到一些參考星使用牽星法靠近到3C273進入60倍目鏡（Pentax XW40）的視野內，很快找到距離它約6'的 10等星 BD +02 2547，以它為參考切換到300倍 (XL 8-24) ，適暗後很容易就看到3C 273。

QSO 3C273 類星體的紅移z=0.158（H-beta線移到了563nm左右），距離我們24億光年之遙！所以進入我眼睛的光線出發時地球還在前寒武紀時代（元古宙）哩，類星體是一種活躍的星系核（AGN），它的光度是一般星系的數千倍，它們中心通常都有個超大質量黑洞。據天文學家們估計3C 273的中央有個約十億顆太陽質量的超級黑洞。

3C 273類星體是目前肉眼透過8"小型望遠鏡在郊山所能見到的最遠的天體了，沒有之二。

今天的另一個目標是測量一些我之前做眼視素描使用過的濾鏡（包括IDAS-P2, CLS, OAKS的LP2即OIII+Hb，此外還有OIII濾鏡以及Hb濾鏡）的減光值，好更精確的計算觀測數據與對比門檻值（請參考我的觀測數據的統計圖表分析，相當吻合人眼對比門檻理論，我很想用「一錘定音」這個詞來形容符合理論的程度，因為我觀測並不是依照理論預測的參數去調整器材的，而是在觀測後才去依理論計算數據並與之預測的辨識門檻做比較）。

此刻天頂亮度19.6 mpsas，正好極接近我過去素描三百個天體的所有背景天空值的中位數，是個非常適合測量濾鏡的時機。

在觀測順利的完成後便開始拍些星景紀錄，久違的三芝陳大哥也上來乘涼了（上次偶遇是在2018年，當時我正在這裡用M210觀測火星大接近），這幾天台北市區相當熱，名符其實的暑氣可蒸人，此刻這裡則相當涼爽。

後來丁兄也上來了，我們小聊了一下。

Because I plan to observe 3C273 tonight, I brought Takahashi's Mewlon 210 with me. The moon phase tonight is about 65%, and it will rise around eleven o'clock, just before midnight (the ridge of ShaoGuanYin Mountain on the eastern side of the saddle blocks the view, so people can observe until around midnight without significant interference from moonlight). Therefore, I only intend to observe during the first half of the night. Additionally, 3C273 is located in the constellation of Virgo, which is a spring constellation. Currently, after nightfall, it is not high in the western sky. I need to observe it before it sets behind the Datun Mountain. Therefore, I specifically set up the equatorial mount before twilight ends tonight. I started observing around eight-thirty.

Astronomical twilight has passed, but it is still early for the night sky to reach its darkest point at midnight. However, the transparency is quite good. Even though the surface brightness of the sky at an altitude of about thirty degrees in the west is still below 19, I can still use a 7x50 finder scope to sequentially locate some reference stars using the star-hopping method. I can then bring the telescope closer to the field of view of 3C273 at 60x magnification (with the Pentax XW40 eyepiece). I quickly found the 10th magnitude star, BD +02 2547, located about 6 arcminutes away from 3C273. Using it as a reference, I switched to 300x magnification (with the XL 8-24 eyepiece) and easily spotted 3C273.

The redshift of the quasar 3C273 is z=0.158 (H-beta line shifted to around 563nm), which corresponds to a distance of 2.4 billion light-years from us! So, when the light that enters my eyes left the quasar, the Earth was still in the Precambrian period (Paleozoic Era). Quasars are active galactic nuclei (AGN) with luminosities thousands of times greater than typical galaxies. They usually have supermassive black holes at their centers. Astronomers estimate that the central region of 3C273 contains a supermassive black hole with a mass of about one billion solar masses.

3C273 is currently the farthest object visible to the naked eye through an 8-inch telescope in suburban areas. There is nothing comparable.

Another goal for today is to measure the attenuation values of some filters I previously used for visual sketching (including the IDAS-P2, CLS, OAKS LP2 (OIII+Hb), as well as OIII and Hb filters) to calculate observational data more accurately and compare them to the threshold values (please refer to the statistical analysis of my observational data spreadsheet , which closely matches the human eye's contrast threshold theory, I would like to use the term "spot-on" to describe the level of adherence to the theory. It's because my observations were not adjusted based on the predicted parameters of the theory; instead, I calculated the data according to the theory after the observation and compared it to the predicted recognition threshold).

At this moment, the zenith brightness is 19.6 mpsas, which happens to be very close to the median value of the background sky for the three hundred celestial objects I previously sketched. It is an excellent opportunity for precise measurements of filters.

After successfully completing the observations, I started taking some astrophotography of the night sky. Mr. Chen from Sanzhi also came up to enjoy the cool breeze (the last time we met was in 2018 when I was observing the close approach of Mars with the Mewlon 210 here). These days, Taipei City is quite hot, with scorching summer heat. But at this moment, it is pleasantly cool here.

Later, Ding (a friend) also joined me, and we had a little chat.

今晚透明度不錯。照片中北極星與小熊座分外明亮。

用手機曝十秒也能曝出不少星星與銀河。（我的手機最長只能曝十秒）

備忘：

1. 使用廣角拍攝的銀河若要以馬賽克磁磚方式接合，那麼各別拍攝的影像需先做背景校正（智慧平場），譬如 Siril的 Background extraction，搭配自動拉曲線（兩次）。

2.接著需將將週邊裁切掉一些，除了週邊小範圍尤其角落圍亮度很難與其他地方一樣校正平整，接起來會有明顯接線，此外週邊的像差也會影響對齊軟體的變形校正判斷。

3.馬賽克接合前要做校色（color match）的動作將所有影像色調統一，譬如在Rigistar下就是對齊後接著將所有影像對基準影像做calibration 。

4.使用Photomerge時若檔案非常多，盡可能先預先做小區域的接合，再進一步讓photomerge接合。此外，merge時可以先接一小部分，看看是否順利，若接不起來是卡在哪個地方，然後以接圖軟體譬如Rigistar先自行做一個銜接的小區塊接圖，也就是有時需要一些trick，讓photomerge能順利接起來。

xxx

3C 273的光譜