日出從某山後 Sunrise from behind a certain mountain

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介紹 Introduction

在燥坑站牌等公車時， 好奇： 一年當中， 哪幾天太陽會從東卯山後出？

While waiting for the bus at the Zao Keng bus stop, we wonder: what days of the year will the Sun rise from behind Dongmao Mountain?

結果 Results

日自東卯山出時刻表： Sun rising out of Dongmao Mountain timetable:

Year MM DD HH MM SS Azim Elv [Skew]
2021-04-26 05:59:55 78.2 6.8 [0.8]
2021-04-27 05:59:11 77.8 6.8 [0.4]
2021-04-28 05:58:29 77.5 6.8 [0.1]
2021-04-29 05:57:47 77.2 6.8 [-0.2]
2021-04-30 05:57:05 76.8 6.8 [-0.6]
2021-05-01 05:56:25 76.5 6.8 [-0.9]

2021-08-12 06:04:31 76.6 6.8 [-0.8]
2021-08-13 06:04:53 76.9 6.8 [-0.5]
2021-08-14 06:05:14 77.2 6.8 [-0.2]
2021-08-15 06:05:36 77.6 6.8 [0.2]
2021-08-16 06:05:57 77.9 6.8 [0.5]
2021-08-17 06:06:19 78.3 6.8 [0.9]

Azimuth: 方位角; Elevation: 仰角; [Skew]: 太陽離東卯山之方位角 degrees of azimuth Sun is from Dongmao Mountain.

每年同天同位置， 僅差幾秒。

Same day and place every year, within a few seconds.

方法 Method

1. Obtain coordinates from OpenStreetMap.

2. Compute azimuth from bus stop to mountain.

3. Compute new horizon, given elevations of bus stop and mountain top.

4. Compute azimuth of sun at new horizon on each day of the year.

5. Filter out days when azimuth is too far.

相片 Photos

算完日期、 時間， 下次我們一定會記得不要只跳上下一般公車， 而留下來拍照。 暫時留本張， 拍攝於：

Now armed with the days and times, we will be sure next time to not just hop on the next bus, but instead stick around to take a picture! But for now here is a picture taken at:

    2020-06-17 06:03:04 69.0 10.6 [-8.4]
    

略似「核爆」。 （東卯山位於中間的北（左）邊較陡的山， 離鏡頭 10 公里。）

Looks rather "nuclear." (Dongmao is the mountain with the steep north (left) side in the middle of the photo, 10 km. away.)

（其實， 將 gamma 調至 18, 更像核爆：）

(As a matter of fact, if we adjust the gamma to 18, it looks even more nuclear:)

原始碼 Source code.

Last modified: 2021-04-13 23:53:34 +0800