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The dusty disk of NGC 247

This highly inclined spiral galaxy is more than a million light-years closer to the Milky Way than was previously thought, bringing its distance down to just over 11 million light-years.
NGC-247-in-Cetus
This chart shows the location of the galaxy NGC 247 within the constellation of Cetus. This map shows most of the stars visible to the unaided eye under good conditions and the galaxy itself is marked as a red oval in a circle. Through a moderate-sized amateur telescope this galaxy appears quite large, but dim, and needs a dark sky to be seen well. ESO/IAU/S&T
This image of NGC 247, taken by the Wide Field Imager on the MPG/ESO 2.2-meter telescope at the European Southern Observatory’s (ESO) La Silla Observatory in Chile, reveals the fine details of this highly inclined spiral galaxy and its rich backdrop. Astronomers say this highly tilted orientation, when viewed from Earth, explains why the distance to this prominent galaxy was previously overestimated.

The spiral galaxy NGC 247 is one of the closest spiral galaxies of the southern sky. In this new view from the Wide Field Imager on the MPG/ESO 2.2-meter telescope in Chile, large numbers of the galaxy's component stars are clearly resolved, and many glowing pink clouds of hydrogen, marking regions of active star formation, can be made out in the loose and ragged spiral arms.

NGC 247 is part of the Sculptor Group, a collection of galaxies associated with the Sculptor Galaxy (NGC 253). This is the nearest group of galaxies to our Local Group, which includes the Milky Way, but putting a precise value on such celestial distances is inherently difficult.

To measure the distance from Earth to a nearby galaxy, astronomers have to rely on a type of variable star called a Cepheid to act as a distance marker. Cepheids are luminous stars whose brightness varies at regular intervals. The time taken for the star to brighten and fade can be plugged into a simple mathematical relation that gives its intrinsic brightness. When compared with the measured brightness, this gives the distance. However, this method isn't foolproof, as astronomers think this period-luminosity relationship depends on the composition of the Cepheid.

Another problem arises from the fact that some of the light from a Cepheid may be absorbed by dust en route to Earth, making it appear fainter, and therefore farther away than it really is. This is a particular problem for NGC 247 with its highly inclined orientation, as the line of sight to the Cepheids passes through the galaxy's dusty disk.

However, a team of astronomers is currently looking into the factors that influence these celestial distance markers. The team has already reported that NGC 247 is more than a million light-years closer to the Milky Way than was previously thought, bringing its distance down to just over 11 million light-years.

Apart from the main galaxy itself, this view also reveals numerous galaxies shining far beyond NGC 247. In the upper right of the picture, three prominent spirals form a line, and still farther out, far behind them, many more galaxies can be seen, some shining right through the disk of NGC 247.

This color image was created from a large number of monochrome exposures taken through blue, yellow/green, and red filters taken over many years. In addition exposures through a filter that isolates the glow from hydrogen gas have also been included and colored red. The total exposure times per filter were 20 hours, 19 hours, 25 minutes, and 35 minutes, respectively.


This sequence gives us a close-up view of the spiral galaxy NGC 247 and its rich backdrop. This picture was taken using the Wide Field Imager (WFI) at ESO's La Silla Observatory in Chile. NGC 247 is about 11 million light-years away in the constellation Cetus the Whale. Through a moderate-sized amateur telescope, this galaxy appears quite large, but dim, and needs a dark sky to be seen well. ESO/Music: John Dyson (from the album Moonwind)
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