Best Hii Region
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An emission nebula in Cassiopeia featuring a roughly 10-light-year-wide bubble blown by stellar winds from the massive O-type star BD+60°2522 into the surrounding interstellar medium.
A bright emission nebula and active star-forming region in Sagittarius about 5,500 light-years away, also called the Swan Nebula for its distinctive curved shape.
A large circular emission nebula in Monoceros roughly 5,200 light-years away, surrounding the young open star cluster NGC 2244 whose radiation ionizes its glowing hydrogen gas.
A large emission nebula in Cygnus whose outline resembles the North American continent, discovered by Max Wolf in 1891 and located roughly 1,600 light-years from Earth.
A large emission nebula in Cassiopeia whose heart-shaped appearance is carved by radiation and stellar winds from hot massive stars in the central young open cluster Melotte 15.
A large emission nebula and active star-forming region in Cassiopeia, often imaged alongside the neighboring Heart Nebula (IC 1805), the pair spanning roughly 300 light-years together.
An emission nebula in Orion located directly adjacent to Alnitak, the easternmost star of Orion's Belt, and energized by ultraviolet radiation from that O-class supergiant.
An emission nebula in Cygnus separated from the adjacent North America Nebula by a molecular cloud, featuring active star formation and prominent ionization fronts along its border.
A large emission nebula in Perseus whose elongated shape resembles the U.S. state of California, primarily ionized by the bright runaway star Xi Persei located about 1,000 light-years away.
An emission nebula and H II region in Cassiopeia containing the young open cluster IC 1590, notable for prominent dark Bok globules silhouetted against its glowing ionized gas.
An emission nebula in Ara sculpted by the young open cluster NGC 6193, whose stellar winds and UV radiation carve towering gas pillars resembling a pair of battling dragons.
An emission nebula in Scorpius about 8,000 light-years away, hosting the massive young star cluster Pismis 24, one of the most luminous stellar groupings in the Milky Way.
An emission nebula in Orion directly adjacent to and physically connected with the Orion Nebula (M42), first observed by Jean-Jacques Dortous de Mairan around 1731.
An emission nebula in Cepheus surrounding the young open cluster NGC 7380, whose pareidolic wizard silhouette is most apparent in narrowband hydrogen-alpha imaging.
An emission nebula straddling the border of Monoceros and Canis Major whose broad wings and curved head closely resemble a seagull in flight when imaged in hydrogen-alpha light.
An emission and reflection nebula in Cygnus at the terminus of the dark nebula Barnard 168, enclosing a young star cluster still embedded in the gas and dust from which it formed.
An emission nebula in Orion forming an active H II star-forming region, featured prominently in a Hubble Space Telescope anniversary image released in 2014 highlighting newborn stars.
An emission nebula in Centaurus about 6,500 light-years away, notable for containing Thackeray's Globules, dark dense clouds studied as candidate sites of ongoing triggered star formation.
A large emission nebula in Scorpius spanning roughly 250 light-years, located about 6,000 light-years away and almost entirely invisible to the unaided eye due to its faint hydrogen-alpha emission.
An emission nebula in Cepheus energized by two embedded Wolf-Rayet stars, whose narrowband hydrogen-alpha imagery reveals a mane-and-face profile resembling a lion.
An emission nebula in Cassiopeia with curved, claw-shaped ionized hydrogen structures, part of a larger star-forming complex associated with the region near open cluster NGC 7538.
A diffuse emission and reflection nebula in Cepheus at the edge of a large molecular cloud, where hot young stars illuminate a cave-like opening in the surrounding dark gas.
An active ionization boundary in the Pelican Nebula (IC 5070) in Cygnus where ultraviolet radiation from young stars sculpts towering pillars and drives ongoing star formation.
An HII region in Cygnus whose Spitzer Space Telescope infrared image reveals a skull-like cavity structure blown by powerful winds from the embedded young star cluster.
A large circular H II region in Orion centered on Lambda Orionis (Meissa), sculpted by stellar winds and UV radiation from the central O-type star and its associated cluster.
A large, low-surface-brightness emission nebula in Orion included in Stewart Sharpless's 1959 H II region catalog and first identified by amateur astronomer Harold Lower.
