The explosion of a star, which can shine for a few weeks as brightly as a whole galaxy. Many are found every year in distant galaxies, sometimes by amateurs, at magnitude 12 to 16. The last one seen in our own Galaxy was in 1604.
Related terms
- Supernova remnant
The expanding debris of a massive star that exploded. The Crab Nebula (M1) is what remains of the supernova seen in 1054; the Veil Nebula in Cygnus is far older and very large. An OIII filter helps a lot with the latter.
- Variable star
A star whose brightness changes over time. Algol in Perseus fades from magnitude 2.1 to 3.4 every 2.87 days when a companion eclipses it; Mira in Cetus swings from 3 to 10 over about 332 days. Amateurs follow thousands of them and share their estimates.
- Galaxy
A vast system of billions of stars, gas and dust held together by gravity. The Andromeda Galaxy (M31), 2.5 million light-years away, is visible to the naked eye as an elongated smudge. In a telescope most look like faint grey glows: their light set off millions of years ago.
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