The Story of Aurora 极光的故事

nationalpark (63)in #cn • 7 years ago

Starry night of Queenstown
星光灿烂的皇后镇

The Story of Aurora

I’ve always been fascinated by Aurora, but did not have a chance see it. Visited Alaska twice, both during the summer. Though, there was no midnight sun at Anchorage, the midnight of July is still bright enough to take clear photos with an ordinary point and shot camera. There is no chance to see Aurora in Alaska during the summer.

A few year ago, I visited the South Island of New Zealand in late December, the summer time of the south hemisphere. When I left Doubtful Sound and heading to Franz Josef Glacier, I stayed one night at Queenstown. The night sky of of Queenstown is not as dark as that of Lake Tekapo and Mt Cook, but still much better than most of the cities around the world.

That night was clear and warm. Good time to shoot the stars. It’s not difficult to photograph the Milky Way if you can find a dark place and have the right equipments. I use Canon 6D, a full frame DSLR, with the maximum iso of 25,600, and a zoom lens of 24-105mm F/4. F/4 is a little slow, but ok. A sturdy tripod is a must, because we need an exposure of about 10-20 seconds. I purchased a Gitzo traveller series 1 tripod for this trip. The Gitzo is not heavy duty, but sturdy, light, and compact. Good for travel.

It’s easy to find a Milky Way exposure calculator online to calculate the setting of the camera and lens. Because the stars are moving, exposure time must be limited to avoid noticeable star trails. The 500 rule means the longest exposure time is 500/focal length. For 24mm, the longest time is about 20 seconds. Exposure calculator would take care of this.

Image stabilization of the lens must be disabled. Otherwise, the image will be blur no matter how sturdy the tripod is. I spent some time to figure out this when I used the tripod for the first time. Auto focus won’t work for the stars. It’s a little challenge to manual focus in the dark. Remember to enable RAW and use brackets for exposures, then all set.

Queenstown is not as dark as Lake Tekapo
皇后镇的夜晚比Tekapo湖要明亮的多

The sky and the mountains of Queenstown are much brighter than that of Mount Cook. Using the parameters of Mount Cook, the night of Queenstown looks like day time in the photo. After took several photos, I found ‘light pollution’ behind a hill far away. Don’t believe there is any city behind the hill and Google map confirmed it. Zoomed in and took more photos of the hill and the lights. Because it’s at the south, the changing hues on different photos make me believe it’s Aurora Australis, the Southern Lights.

"Light pollution" behind the hill
小山后的“光污染”

Queenstown’s latitude is 45 degrees, half way between the equator and the south pole. It’s rare to see Aurora at this latitude. Checked Aurora forecast online. It shows the Aurora was strong at that time, and will be stronger a few hours later. Therefore, I find a better position and keep shooting. The lights change all the time. At last, I took the photo of the splendid purple and green Aurora.

Aurora Australis
南极光

Aurora and Satellite
南极光和卫星

Two more photos of Aurora 另外两张极光照片

Once, I flew to New York City from China during the Fall. The airliner passed Siebra and flew over the Arctic Ocean. Read the news about Aurora Borealis outburst during those days, I expected Aurora during the flight. When it’s dark, I opened the window and saw the green Northern Lights. The lights became stronger and stronger when we were closer to the North Pole, like green glowing clouds stretching hundreds of miles surrounding us. The lights were so bright, that I was able to take photos with my iPhone. The Northern Lights were visible all the way for the rest of the trip. When the plane arrived New York City area, 10,000 feet above ground, I could still see the lights glowing far away over the Horizon. When the airplane descended, the Aurora submerged in the lights of the city gradually.

Aurora Borealis, taken by iPhone in an airplane. Only the brightest part can be shown in the photo
飞机里手机拍的北极光。只有最强的部分能拍下来

极光的故事

对极光一直神往，但是没有机会去看。曾经去过阿拉斯加两次，但是都在夏天。七月的安克雷奇太阳晚上十点才落，凌晨时分户外还十分明亮，可以直接用傻瓜机拍照。夏天的阿拉斯加不可能看到极光。

几年前的十二月去新西兰南岛旅游。在那半球那时是夏天。离开疑湾开往弗朗兹约瑟夫冰川的路上又一次夜宿皇后镇。皇后镇的夜晚远没有Tekapo湖和库克山那样暗黑，但是比其他地方的城市还是少了很多光污染。

那个夜晚晴朗而温暖，是拍星空的好时机。只要有合适的设备，拍银河并不难。我用的佳能6D最高感光度25,600，镜头是24-105 F/4。F/4的光圈有点小，但是还可以用。有个坚固的三脚架很重要，因为要曝光10-20秒左右。为了拍星空我专门买了Gitzo Traveller 1。这款三脚架虽然承重小，头也不是很理想，但是非常坚实轻便，适于旅行。

网上很容易找到拍银河的曝光计算器，会根据片幅，iso，焦距，光圈计算合适的设置。对于一定焦距和片幅拍星星的曝光时间有限制，如果过长会留下星轨，因为星在移动。五百法则说最长曝光时间等于500除以焦距。对于20mm镜头，最多曝光20秒才不会留下明显的星轨。网上的曝光计算器都会考虑星轨问题。

另外，镜头如果有防抖功能一定要关掉，否则画面会模糊。第一次试用三脚架时候花了些时间才明白这一点。镜头自动对焦不能用，必须手动。黑夜里手动对焦有点难，需要一点耐心。另外记住用RAW格式以及包围曝光就齐活了。

皇后镇的夜空和群山比库克山要亮很多。用当初在库克山拍照的设置在这里拍出来的照片像大白天，降低几档才行。拍了几张银河的照片以后发现远处一座小山后面有“光污染”。相信那个地方没有什么城市。查了一下谷歌地图也确实没有，于是用长焦距冲着那个方向增加曝光又拍了几张。因为是南方，而且照片里光的色调不断变化，猜测是南极光。

皇后镇南纬45度，处于赤道和南极的中点。这么高的维度很难看到极光。网上查了一下极光预报，得知当时极光较强，而且再过几个小时会更强。于是选了个更好的位置，继续拍摄了几个小时。极光不断变化，最后拍到了比较明亮的紫色到绿色渐变的南极光。

后来一个秋天，乘飞机从中国飞纽约，穿越西伯利亚飞到北冰洋。记得新闻上看到极光大爆发，天黑以后打开舷窗，看到远处绿色的北极光像发着荧光的云。越靠近北极极光越强，直到飞机被极光环绕。极光很亮，甚至可以用手机拍下模糊照片。一点遗憾是当时轻装出行没有带单反。后面的行程一路极光相伴，直到飞到纽约的上空还可以看到遥远的地平线上方亮着微弱的荧光。飞机下降时，极光才逐渐被淹没在城市的灯光中。