W Orionis is a semi-regular star that is very easy to find and observe. It is easily found close to the naked eye star pi-six, which marks the bottom end of Orion’s bow.
W Orionis varies between 5.9 and 7.7, with a period of about 212 days. It’s variations can be easily followed with a small pair of binoculars, and is best observed once a week.
W Orionis is an example of a carbon star. Carbon stars are red giant stars, which have more carbon in their atmospheres then oxygen. All the oxygen combines with carbon, to form carbon monoxide, and the remaining, excess carbon is then left to form other carbon compounds. It is these carbon compounds which filter out blue light, making the stars appear more red then they would otherwise appear.
It’s the intense redness of carbon stars which can make them challenging to estimate. It’s best not to stare at the star for too long, and to instead take quick glances, otherwise the star may appear brighter then it actually is.
| Extreme brightness range | 5.9 – 7.7 |
| More typical range | 5.9 – 6.9 |
| Period of variation | 212 |
| Frequency of observation | Once a week |
| Observe using | Best observed with 50mm binoculars. |
| Visibility | Best observed October to March |
