The California Nebula
Also known as NGC 1499, the California Nebula is one of the most popular targets for astrophotographers. It is a star-forming region located in the Orion Arm of the Milky Way Galaxy. Its isolated position in the Perseus constellation makes it very noticeable on long-exposure photographs. The Nebula is about 2.5° across, which covers the apparent size of 5 full Moons. However, it is about 100 light-years long. At 1500 light-years away from Earth, it is one of the closest HII regions. Its equatorial coordinates are 04h 03m 18.00s of RA and +36° 25′ 18.0″ Dec.
The origin of the name of the California Nebula is its resemblance with the shape of the US state of California. It was discovered by the American astronomer Edward Ernest Barnard in 1884 in one of his photographs. It lies 12 degrees away from the Pleiades, the famous open star cluster and reflection nebula of the Taurus constellation.
With an apparent magnitude of 6, it is observable with the unaided eyes in very dark skies only. A pair of binoculars and specific filters – that we will mention below – would make it easier to see. However, details will appear if we take long-exposure photographs only.
Its large span makes it hard to observe wholly. We would preferably choose a large-field telescope to have a complete and detailed view of the Nebula in a single frame.
NGC 1499 is an intense hydrogen emission nebula. As seen in this picture (upright), near the California Nebula, there is a very energetic blue giant called Menkib (or Xi Persei), a star whose mass is about 40 solar masses. Its apparent luminosity is roughly 13,000 times that of the Sun and emits about 330,000 more amount of light. Menkib is a runaway star, which means that it is running faster than expected. It is thought to be born in the California Nebula a few million years ago. The radiation from this star ionizes the hydrogen atoms in the surrounding nebular gas and makes it radiate in H-alpha (red) and H-beta
(blue-green) wavelengths. The red light is characteristic of the hydrogen atoms recombination with electrons removed by the energetic radiation of Menkib.
We can see these radiations clearly in this composite picture. This picture, as well as the previous one, was taken using a ZWO Kamera mounted on a Celestron RASA F2.2 for a total exposure time of 6.7 h to collect maximum light from the object. Besides, with the use of Baader f/2 Highspeed 2″ H-Alpha and OIII filters, the photographer obtained the red and blue colours.
Infrared images of NGC 1499, such as those of the Wide-field Infrared Survey Explorer (WISE), reveal the existence of a hot dust cloud near Xi Persei. This heat comes from the shock wave that occurs between the fast stellar jets that the star blows and the dust cloud in its neighbourhood. Infrared photographs allow us to see dust through the gas. Dust, in infrared images, is usually represented in green (12 microns) and red (22 microns), according to the energy (or heat, equivalently) of the object. More energetic colours, like blue (3.4 microns) and cyan (4.6 microns), represent more energetic (or hotter) objects,
The night sky is full of celestial treasures. While some are visible to our eyes, many more are hidden in the layers of the cosmos. We need more sophisticated equipment to be able to observe them and understand the physics behind them.
Fun fact: NGC 1499 transits in the zenith in central California because the latitude matches the declination of the Nebula.