APOD 3.7

This cosmic cloud looks very similar to the outline of California.  It is drifting through the Orion Arm of the spiral Milky Way Galaxy.  The Sun lies within the Milky Way's Orion Arm and is only about 1,500 light-years from the California Nebula, also known as NGC 1499.  The classic emission nebula is around 100 light-years long.  The most prominent glow of the California Nebula is the red light characteristic of hydrogen atoms recombining with long lost electrons, ionized by energetic starlight.  But in this photo, hydrogen in colored green while sulfur is mapped to red and oxygen to blue.The bright, hot, bluish Xi Persei, is the star most likely providing the energetic starlight that ionized much of the nebular gas.  The California Nebula can be spotted with a wide-field telescope under a dark sky toward the constellation of Perseus, not far from the Pleiades.