Credit: Derek Santiago
Key Takeaways:
- NGC 7662, a planetary nebula colloquially known as the Blue Snowball, is located within the northern region of the constellation Andromeda, approximately 4.5° east of the star Omicron Andromedae.
- Discovered by William Herschel on October 6, 1784, this object exhibits an apparent magnitude of 8.3 and spans 2.2 arcminutes, contributing to the concentration of its light which enables the perception of color.
- Observer accounts of its hue vary from various shades of blue to occasional light green, a phenomenon attributed to individual differences in color perception.
- Structurally, NGC 7662 appears as a uniformly illuminated disk through moderate apertures, revealing a prominent inner ring of gas surrounding a hollow center, which is further encompassed by a more tenuous outer gas shell.
If you have access to an 8-inch or larger telescope, look in the northern part of the constellation Andromeda the Princessfor a planetary nebula called the Blue Snowball. Insert an eyepiece that will give you a magnification around 100x, and you’ll see immediately why astronomers gave it that name. Specifically, point your scope roughly 4½° east of the magnitude 3.6 star Omicron Andromedae.
German-born English astronomer William Herschel discovered this object October 6, 1784. He used what he normally called his 7-foot reflector, which was a Newtonian reflecting telescope with an aperture of 6.3 inches.
The Blue Snowball shines at magnitude 8.3, which is reasonably bright for a celestial object. Luckily, its light isn’t spread out over a large area. NGC 7662 — another designation for this object — measures only 2.2′ across. This small size concentrates the planetary’s light, allowing it to trigger your eyes’ color receptors. If you’re looking for (or wanting to show somebody) color in a deep-sky object, look no further than the Blue Snowball.
That being said, different observers have described it as pale blue, faint blue, light blue, Robin’s-egg blue, slightly blue, whitish-blue, and, occasionally, various shades of light green. What’s more, nobody’s wrong. Each of us has our own sense of color perception, and it may differ a little or a lot from the observer next in line.
Through an 8-inch scope, the Blue Snowball appears as a small, evenly illuminated disk. You won’t see the 13th-magnitude central star in anything less than a 16-inch scope, so search for other details, like the nebula’s rich inner structure.
Look for a bright ring of gas surrounding NGC 7662’s hollow center. A fainter gas shell — tough to see — encompasses the ring. The ring’s brightest areas lie to the northeast and southwest. At magnifications above 300x, the brightness of the shell drops quickly near its edge.
