Hamburger Galaxy — ししの銀河

NGC 3628 is a large edge-on spiral galaxy in Leo, about 35 million light-years away, forming the third member of the famous Leo Triplet along with M65 and M66. It is universally known as the Hamburger Galaxy for its unmistakable appearance: a thin, elongated disk bisected by a prominent dark dust lane — like a cosmic sesame bun. The galaxy's disk is distorted by gravitational interactions with M65 and M66, creating a long tidal tail extending some 300,000 light-years into intergalactic space (visible only in deep photographs). The Leo Triplet is one of the most-photographed galaxy groups in the northern sky.

Part of a three-galaxy feast. In a 4-inch telescope at low power, all three members of the Leo Triplet fit in the same eyepiece field — a compact group of three distinct galaxies at different angles: M66 round and bright, M65 elongated and bright, and NGC 3628 a long thin streak. An 8-inch at 100-150x clearly shows the dark equatorial dust lane splitting NGC 3628 lengthwise — a stunning, almost photographic view. Larger apertures reveal subtle warping in the disk from the tidal interactions. The Triplet lies about 5 degrees east of Theta Leonis. Best observed February through May.

Discovered by William Herschel on April 8, 1784, the same night he recorded several other Leo galaxies. Why Messier missed NGC 3628 when he cataloged its neighbors M65 and M66 is another classic puzzle: M65 and M66 are at magnitude 9.3 and 8.9 respectively, only slightly brighter than NGC 3628 at 9.5, and they are all in the same field. Most historians suspect Messier simply didn't look long enough at the region. The 'Hamburger Galaxy' nickname emerged in mid-20th century amateur astronomy.