C36

About

NGC 4559, a spiral galaxy in Coma Berenices that sits between barred and regular forms, and part of the group called Coma I. Its distance is given as about 24.6 million light-years by non-redshift methods, though one source says 29 million. A supernova appeared in it in 1941, and a luminous blue variable there has erupted repeatedly.

Imaging tips

• About 10.6′ × 4.8′, so at 2,290–3,810 mm on APS-C it spans a third to half of the frame. One imager calls it a rather small target and thinks that is why it is photographed less often.
• Faint for its size at 22.8 mag/arcsec², so plan many hours of broadband data; one published image totalled about 20 hours, with luminance the largest share at nearly 10.
• That image also blended in 3 nm Hα data taken with the same mono camera, while a separate one-shot colour set made up about 7 hours of the total.
• Even a 35 mm f/3.9 smart telescope with no filter has recorded it, though it stays small in a lens that wide.
• Best in March and April; it peaks near 68° altitude from 50°N.