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NGC 6572 - The Blue Racquetball / Emerald Nebula

The Blue Racquetball / Emerald Nebula in Ophiuchus
(click image to see larger version)

Also called the "Emerald Nebula", this is a very small (11 arc-seconds!), bright planetary nebula with high surface brightness. At low magnification it appears to be a star, but its intense blue-green color betrays that is much more than a star!

In order to provide an adequate presentation of this small nebula, I chose to capture it with the 8" LX90 telescope at a focal ratio of f/10. The DSI II Pro combined with the LX90 provide for an approximate magnification of 250x. Such high magnification requires an evening with good seeing. This successful capture of the nebula was preceeded by failed attempts on two prior evenings, when seeing conditions would not support imaging at the slow focal ratio of f/10. The third attempt did prove to be the charm!

I obtained 82 minutes of luminous data, but chose not to use it for the image. Even using 1 minute exposures, the core of the nebula was blown out by the sensitive DSI II Pro camera. As it turned out, the RGB data provided more accurate contour data for the nebula. Stars dimmer than magnitude 16 are visible in this image, in spite of light pollution present at level 9 on the Bortle scale during hot and humid summer evenings (see map:

Equipment: Meade 8" Schmidt-Cassegrain telescope, Meade DSI II Pro, 2" scope adaptor, IDAS LPS light pollution filter, Meade LRGB filter set, Atik filter wheel. Outback Cooler (images captured at an average ambient temperature of about 90°F).

Guiding: AT80ED@f/6.9 piggy-back on LX90, Meade DSI II Pro, IR filter.

Settings: gain: 100, offset: 50, 60s exposures,
RGB: 34:52:55, total exposure time: 2 hours, 21minutes.

Images captured and guided with Envisage software, telescope controlled with AutoStar Suite software.

Post-processing: RGB images stacked with Envisage, Drizzle applied. Registration performed in AIP4WIN. FITS files imported into Photoshop CS for color image creation, color adjustment, and slight brightening enhancement.

This image was created with the help of the ESA/ESO/NASA Photoshop FITS Liberator.

NGC 6572

Apparent Magnitude: 9.0
Apparent Diameter: 0.1 arc-minutes
Distance: 3500 light years

Location: Watauga Skies Observatory, Watauga, Texas
Date: July 29, 2009

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