Explanation: Enjoying the 2004 Transit of Venus from Stuttgart, Germany, astronomer Stefan Seip recorded this fascinating, detailed image of the Sun. Revealing a network of cells and dark filaments against a bright solar disk with spicules and prominences along the Sun's limb, his telescopic picture was taken through an H-alpha filter. The filter narrowly transmits only the red light from hydrogen atoms and emphasizes the solar chromosphere -- the region of the Sun's atmosphere immediately above its photosphere or normally visible surface. Here, the dark disk of Venus seems to be imitating a giant sunspot that looks perhaps a little too round. But in H-alpha pictures like this one, sunspot regions are usually dominated by bright splotches (called plages) on the solar chromosphere.

Sorry I didn't get the APOD posted yesterday. Here it is:

Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2004 June 10

Venus at the Edge
Credit: D. Kiselman, et al. (Inst. for Solar Physics), Royal Swedish Academy of Sciences.

Explanation: With Venus in transit at the Sun's edge on June 8th, astronomers captured this tantalizing close-up view of the bright solar surface and partially silhouetted disk. Enhanced in the sharp picture, a delicate arc of sunlight refracted through the Venusian atmosphere is also visible outlining the planet's edge against the blackness of space. The arc is part of a luminous ring or atmospheric aureole, first noted and offered as evidence that Venus did posses an atmosphere following observations of the planet's 1761 transit. The image was recorded using the 1-meter Swedish Solar Telescope located on La Palma in the Canary Islands. For the Institute for Solar Physics, Dan Kiselman, Goran Scharmer, Kai Langhans, and Peter Dettori were at the telescope, while Mats Lofdahl produced the final image. Excellent movies of the transit - including one of the emergence of Venus' atmospheric aureole - are available from the Dutch Open Telescope, also observing from La Palma.

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