Mercury's tail was captured Using an Edmund Optics 589 nm, 10nm bandwidth filter in an custom 3-D printed enclosure
Borg 90FL, f/4 fluorite refractor
ZWO ASI 294MM pro camera, cooled to -10C
17 x 60 second photos, calibrated and stacked to reveal the fain tail of the planet Mercury
A 24 million km long plume of gas is ejected from Mercury's thin atmosphere due to the sun, very much like a comet.
This is only visible using a narrowband filter that captures the bright yellow sodium light at 589nm.