Crab Nebula is a supernova remnant observed in 1054. Record of those days is recorded on the ancient documents in the world, except for the Europe. It is also referred to as M1 since it is the first catalogued object of the Messier Catalogue. In the Messier Catalogue, however, Crab Nebula is the only supernova remnant. A pulsar exists in the center of Crab Nebula, and also now, it is shinning with the energy supplied from a pulsar. By courtesy of the Subaru Telescope / NAOJ
1054年に爆発の光が観測された超新星の残骸で， 当時の輝星の記録は西洋以外は世界のあちこちの古文書に残されています． メシエ天体の筆頭登録天体でM1とも呼ばれますが， メシエ天体では唯一の超新星残骸です． かに星雲の中心にはパルサーが存在し， パルサーから供給されるエネルギーでいまでも光っています．	Name M1/NGC1952 Right Ascension 05h34m Declination +22 °01′ Apparent Diameter 5′ Distance 7200 light years

Optical Spectrum of M1

This is the optical spectrum of M1 observed by GCS (Gunma Compact Spectrograph) of the Gunma Astronomical Observatory. Upper image of spectrum, the width expresses wavelength and the length expresses the direction of space. Lower graph of spectrum, the width expresses wavelength and the length expresses the intensity of light. The Clab Nebula is expanding with speed about 1200 km/s. Therefore, on the spectrum, emission line bends circularly by the doppler effect, and the line which expands to an opposite side also can be seen. Moreover, since the substances which are blowing away for every place is also different, the intensity of emission also differs fairly for every place. In addition, the straight line spectrum of a horizontal direction is the stellar element which overlapped with the slit. In upper image, the name of the ion surrounded by [ ] is the special line called the forbidden line, such as [OIII], [NII] and [SII]. These are typical spectra of nebula. ぐんま天文台のGCS（小型低分散分光器）で観測した， かに星雲M1の可視光スペクトルです． 上のスペクトル画像は，横方向が波長，縦が空間方向を表し， 下のグラフは，横方向が波長，縦が光の強さを表しています． かに星雲は約1200km/sという速さで膨張しているため， スペクトル画像上では，輝線がドップラー効果によって円弧状に曲がり， 反対側に膨脹する成分も見えています． また，吹き飛んでいる物質は場所ごとに違いがあり， 輝線の強さも場所ごとにずいぶんと異っています． なお，水平方向の直線状のスペクトルは，スリットに重なった星のものです． 一方，下のグラフの中の[OIII]や[NII]や[SII]は， 酸素や窒素やイオウの禁制線と呼ばれる特殊なスペクトル線で， 非常に希薄なガスから放射される特徴的なスペクトル線です． これは典型的なガス星雲のスペクトルです． Forbidden Line and Recombination Line By courtesy of H.Kawakita, K.Kinugasa (Gunma Astronomical Observatory)