Messier 55 or NGC 6809
318 of 356

Messier 55 (or NGC 6809)

April 26, 2005
The present photo is a reproduction of a digital image that was obtained in the early morning of June 6, 1998. It shows the central part of the southern globular cluster Messier 55 (or NGC 6809) in the constellation Sagittarius. The exposure lasted 30 seconds and was made with the VLT Test Camera through an optical filtre isolating mostly red light (570 - 700 nm). It is here shown exactly as it was obtained ("raw image"), without any image processing . The brightness level in the reproduction has been set so that the fainter stars are well visible. The field shown is 83 x 83 arcsec; each pixel measures 0.0455 arcsec.

Images of a large number of stars over the entire field have been measured and consistently show a stunning image quality. The full-width-at-half-maximum (FWHM) is only 0.27 arcsec ! Moreover, the images are very nearly round - the measured image elongation is negligible at the 5% level (0.015 arcsec).

This capability used on earth would allow us to clearly see the two headlights of a car at a distance of no less than 1200 kilometres (the distance from Paranal to Santiago de Chile) - an astonishing performance of a ground-based telescope. It confirms that the VLT will be able to take full advantage of moments of particularly good observing conditions at Paranal and may soon begin to look beyond current horizons.

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