Page "Altair" Paragraph 9

Altair is one of the few stars for which a direct image has been obtained.

In 2006 and 2007, J. D. Monnier and his coworkers produced an image of Altair's surface from 2006 infrared observations made with the MIRC instrument on the CHARA array interferometer ; this was the first time the surface of any main-sequence star, apart from the Sun, had been imaged.

The false-color image was published in 2007 and can be seen above and to the left ; the brighter regions are shown in white and darker regions in blue.

In this image, North ( the direction towards the North Celestial Pole ) is up and East is left, and the white line is the rotational axis of Altair.

The black grid shows lines of latitude and longitude in an Altair-centric coordinate system.

The von Zeipel effect can be observed in the image, which shows a white spot near the pole and a darker equator.

The equatorial radius of the star was estimated to be 2. 03 solar radii, and the polar radius 1. 63 solar radii — a 25 % increase of the stellar radius from pole to equator.