The California Nebula (NGC 1499) is an intense hydrogen emission nebula located in the constellation Perseus. This iconic deep-sky object has been ignited by energetic starlight that has ionized its nebular gas composition. The most noticeable characteristics of this nebula are its striking resemblance in shape to the US state of California, and red color due to its hydrogen composition. It is almost 2.5° long on the sky and, because of its very low surface brightness, it is extremely difficult to observe visually.
The Rosette Nebula is a cloud of dust containing enough gas and dust to make about 10,000 stars like our Sun. In the centre of the nebula, and off to the right hand side of this image, is a cluster of hot, bright young stars. These are warming up the surrounding gas and dust, making it appear bluer. The small, bright white regions are cocoons of dust in which huge stars are currently being born. These “protostars”, each one of which will probably become a star up to ten times more massive than the Sun, are heating up the surrounding gas and dust and making it clow brighter. The smaller, redder dots on the left side and near the centre of the image also contain protostars, but these are smaller, and will go on to form stars much like our Sun. Just as the centre of the nebula contains bright young stars, in a few tens or hundreds of millions of years these stars will have died, but the protostars will have evolved into fully-fledged stars in their own right. In this way, the star formation will move outwards through the nebula.
