https://earthsky.org/space/how-to-capture-mercurys-sodium-tail/How can astrophotographers capture Mercury’s tail? Mercury’s tail is brightest within 16 days of perihelion, the planet’s closest point to the sun. Mercury reaches perihelion every 88 days (it takes 88 days to orbit the sun once). Mercury was 16 days past perihelion on May 13, 2021, when Steven Bellavia took the first photo on this page of Mercury’s sodium tail.
Bellavia told EarthSky that an article at Spaceweather.com on May 10, 2021, inspired him to try to photograph Mercury’s sodium tail, using a 589 nanometer (nm) wavelength filter that lets the sodium light signature through. After reading about it, he was eager to try it for himself. He explained:
On the morning of Wednesday, May 11, I ordered a 589 nm narrowband filter, with 10 nm of bandpass [the wavelength range of the filter], from Edmund Optics. A friend who owns a 3D printer printed me two rings I designed to hold the filter, as the filter did not come with standard mounting used in astronomy. I used the new setup within hours of getting it all together.
Bellavia captured photos of Mercury’s tail on both May 13 and 14, 2021 – the first and second photos on this page – using a tracking German equatorial mount affixed with a Canon 100mm lens and the filter mounted in front of the lens. On the first night he took 30 exposures of 30 seconds each, while on the second night he took 20 exposures of 60 seconds each using a Borg 90mm refractor. He said:
On the second night, having seen the results from my first attempt, I realized that it would be better to have the telescope and mount track on Mercury itself, as the tail is faint, and all photons collected need to land as frequently as possible on the same pixels in each individual image to reveal it. Also note that on both nights, I would have liked to have taken many more images, but I needed to wait for the background sky to be dark enough to reveal the tail. But Mercury was also setting at this time, either behind land or into clouds near the horizon.
Even with these limitations, Bellavia’s photos of Mercury’s sodium tail are remarkable. Read more about Bellavia’s camera setting here and here at EarthSky Community Photos, and check out his setup and gear for photographing Mercury’s sodium tail at his page on Flickr.
觀星論壇 
