Runaway Star Paints the Sky

The California Nebula over Caradon Observatory, 26th Mar 2020

It's surprising just how far some deep sky objects stretch across the sky. This composite shows a deeper exposure aligned over a wide-angle image of the Caradon Observatory site. The outer Milky Way runs from upper left to lower right, from Gemini to Cassiopeia. Visible above the trees is the red smear of NGC 1499, the California Nebula, to scale with the foreground image. It covers some 3 degrees of the sky, six full Moons across. While invisible to the naked eye it's not that far out of sight, making a challenging binocular target. However, in long-exposure photographs it's one of the brightest nebulae in the sky.

NGC 1499 in Perseus

A closer view shows its structure, glowing red from ionised ​hydrogen with hints of blue from glowing oxygen giving it a pink hue. Dark features are concentrations of dust, often sites of star formation. It's a vista sculpted by natural processes - stellar winds and radiation pressure from bright stars, and gravity.

Xi Persei, approach with care

The star Xi Persei is responsible for lighting up the nebula, visible just below centre frame. Also known as Menkib, it's one of the hottest stars in the Milky Way with a surface temperature of 35,000 C. If placed at the centre of our solar system it would be an impressive sight, at 14 times solar diameter, but one best viewed from a distance. Its brightness is a staggering 250,000 times that of our Sun. It would be difficult to appreciate from the Earth as everything would burst into flames and, within a few seconds, the oceans would start to boil. Even from the night-side of the Earth it would be obvious that something was up, the other planets and brighter asteroids would flare like beacons. And if the Moon was up it would shine almost as brightly as our Sun, simply from reflected starlight.

Xi Persei is a runaway star, ejected from its birthplace either by a close encounter with another star or the supernova of a companion. A chance encounter has brought it close to a molecular cloud, making the California Nebula visible. The plane of the Milky Way is littered with these concentrations of gas and dust, largely invisible in the visible spectrum but detectable by radio and infra-red telescopes. The nebula is just an optically bright feature of a much larger complex. If Xi Persei had been launched in another direction it might well have painted, and to a degree sculpted, an entirely different deep sky object.

Taurus & Perseus

Large, bright nebulae such as NGC 1499 do not require a telescope to photograph. In the landscape image it's just possible to see the small imaging rig trained on it.

NGC1499 in Hydrogen Alpha

The monochrome image above was taken using a short telephoto lens on the 26th March and blended into a colour image taken previously. Imaging it with a telescope usually requires shooting separate panes to stitch together in a mosaic, as it will not fit within the field of view. This spectacular 103 hour effort by Sara Wager shows the nebula in intricate detail  and is best viewed on a large high-resolution monitor.