The Pacman Nebula (NGC 281) is a large emission nebula appearing near the orange giant Schedar in the constellation Cassiopeia. The nebula lies approximately 9,200 light years away and occupies 35 arcminutes of the apparent sky. It is also catalogued as IC 11 and Sharpless 184 (Sh2-184). It was named the Pacman Nebula for its resemblance to Pac-Man, the character in the popular 1980s maze video game. In optical images, a dark dust lane forms the Pac-Man’s mouth.
The Pacman Nebula stretches 48 light years across. It is a star-forming region that contains young stars, large dark dust lanes and Bok globules. Bok globules are small, dense dark nebulae packed with material from which new stars are formed. The dark dust lane spreads unevenly across glowing clouds of hydrogen and its appearance suggests that it being sculpted by a massive star in the background, concealed by the dark clouds.
NGC 281 is associated with IC 1590 (Collinder 8), a young open cluster with an estimated age of 3.5 million years. The main sequence stars in the cluster are luminous blue stars of the spectral types O6.5 to B9.5. The spectral types of the pre-main sequence stars range from A8/9 to G8. The cluster has an apparent magnitude of 7.4. It contains 279 stars of magnitude 17 or brighter, including the multiple star system responsible for ionizing the gas in the nebula and making it glow. The O-type trapezium system lies near the centre of the nebula.
Catalogued as B 1 or β 1 (Burnham 1), HD 5005, HIP 4121 and ADS 719 ABCD, the star system is composed of an O-type star with an apparent magnitude of 7.8 and four companions. The companions are separated by 1.4 to 15.7 arcseconds from the primary. The physical separation between the main components of the trapezium system is between 4,000 and 26,000 astronomical units. The system was discovered by the American astronomer Sherburne Wesley Burnham (1838 – 1921). The Catalog of Components of Double & Multiple Stars (CCDM) lists five components with apparent magnitudes of 7.9, 9.9, 8.9, 9.4, and 12.1, while The Washington Visual Double Star Catalog lists as many as 17 components.
NGC 281 was discovered by the American astronomer Edward Emerson Barnard in August 1883. It is one of the several well-known nebulae in the constellation Cassiopeia. The others are the Heart and Soul nebulae (IC 1805 and Westerhout 5) near the border with Perseus and the Bubble Nebula (NGC 7635) near Cepheus.
The Pacman Nebula lies in the Perseus Spiral Arm of the Milky Way. Named after the constellation Perseus, in which it is seen, the Perseus Spiral Arm is one of our galaxy’s two major spiral arms. The other one is the Scutum-Centaurus arm. The Perseus Spiral Arm is believed to lie about 6,400 light years from the Sun and have a radius of about 10.7 kiloparsecs. It is over 60,000 light years long and about 1,000 light years wide.
The Pacman Nebula is very easy to find because it lies near Cassiopeia’s W, one of the most distinctive asterisms in the northern sky. It appears just east (left) of Schedar (Alpha Cassiopeiae), the bottom right star of the “W,” and south of the binary star Achird (Eta Cassiopeiae). The nebula is easily visible in small telescopes.
Pacman Nebula – NGC 281
|Right ascension||00h 52m 59.35s|
|Declination||+56° 37′ 18.8″|
|Apparent size||35 arcminutes|
|Radius||48 light years|
|Distance||9,200 light years (2820 parsecs)|
|Names and designations||Pacman Nebula, NGC 281, IC 11, Sharpless 184, Sh2-184, LBN 616, LBN 123.17-06.28|