Home Galleries Imagers Resources Support Members Exposure Sign In

Imager: Paul Robertson Object: Sun. Name: None Type: Sun Constellation: Zodiacal Site: Newcastle under Lyne, United Kingdom Date/Time: 9/19/2009 12:05:00 PM Telescope: Sky Watcher BK15012EQ6 Optical System: Refractor Mount: Other German Equatorial Mount Type: German Equatorial Camera: DMK 21AU04 (IS-1MU/CU) Camera Type: Web Cam Click Here For Larger Image         Object: The photosphere of an astronomical object is the region from which externally received light originates. The term itself is derived from Ancient Greek photos meaning "light" and sphaira meaning "ball," in reference to the fact that it is a ball-shaped surface perceived to emit light. It extends into a star's surface until the gas becomes opaque, equivalent to an optical depth of approximately 2/3. In other words, a photosphere is the deepest region of an luminous object, usually a star, that is transparent to photons of certain wavelengths. The Sun's photosphere has a temperature between 4500 and 6000 Kelvin (with an effective temperature of 5800 Kelvin) and a density of about 2 × 10-4 kg m-3; other stars may have hotter or cooler photospheres. The Sun's photosphere is composed of convection cells called granules—cells of gas each approximately 1000 kilometres in diameter with hot rising gas in the centre and cooler gas falling in the narrow spaces between them. Each granule has a lifespan of only about eight minutes, resulting in a continually shifting "boiling" pattern. Grouping the typical granules are super granules up to 30,000 kilometres in diameter with lifespan of up to 24 hours. The Sun's visible atmosphere has other layers above the photosphere: the 2,000 kilometre-deep chromosphere (typically observed by filtered light, for example H-alpha) lies just between the photosphere and the much hotter but more tenuous corona. Other "surface features" on the photosphere are solar flares and sunspots.         Image: This magnificent image of an active region within the Sun's upper atmosphere captures to perfection the grainy nature of the solar photosphere. This is a modern day version of the pioneering photograph taken by Pierre Janssen in 1877 with a 135 mm refractor at the new Paris Observatory situated at Meudon. This was the first photograph taken which revealed in great detail the nature of our sun’s atmosphere. Paul Robertson’s image lives up to the great tradition of pioneering solar astrophotographers like Jean Foucault, Warren de La Rue and Pierre Janssen. Paul is to be congratulated.         Imager: Paul Robertson is a Lunar and Solar Astrophotographer from the United Kingdom. He images from a site near to Newcastle-under-Lyne, Staffordshire, England.