Two relatively large edge-on galaxies, the Whale (NGC 4631) and the Hockey Stick (NGC 4656–7), lie 25 million light-years away toward the constellation Canes Venatici the Hunting Dogs. Because of the mass and energy of these objects, a weak gravitational interaction occurs between the two, and it affects their neighboring dwarf galaxies as well. This force pulls material from one galaxy to the other, distorting their shapes and triggering star formation.
You’ll find the pair nearly halfway down and a tad southeast of an imaginary line between Cor Caroli (Alpha [α] Canum Venaticorum) and Gamma (γ) Comae Berenices. You’ll likely spot NGC 4631 first. Shining at 10th magnitude, it’s one of the brightest edge-on galaxies in the sky. It spans 17' by 3.5' and has a small elliptical galaxy, NGC 4627, hovering 2.5' to its northwest. Together, they form Arp 281 from Halton Arp’s Atlas of Peculiar Galaxies. Pegged as the Whale for its unusual wedge shape, it doesn’t take much to imagine NGC 4631 as Earth’s largest mammal drifting through the eyepiece, with the small elliptical galaxy as its spray.
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