Celestial hemisphere:  Southern  ·  Constellation: Sagittarius (Sgr)  ·  Contains:  HD161716  ·  Little Gem  ·  NGC 6440  ·  NGC 6445  ·  PK008+03.1
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NGC 6445 and NGC 6440, Gary Imm
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NGC 6445 and NGC 6440

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NGC 6445 and NGC 6440, Gary Imm
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NGC 6445 and NGC 6440

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Description

This field of view captures two objects, a planetary nebula (NGC 6445) and a globular cluster (NGC 6440), in the southern constellation of Sagittarius at a declination of -20 degrees. It is rare to be able to see a planetary nebula and a globular star cluster in the same field of view. This image combines narrowband and RGB to capture both nebula detail and star color.

The planetary nebula spans 3 arc-minutes in our apparent view. It is one of the largest PN (and therefore also one of the oldest) at a true diameter of 4 light years. It lies 4,500 light-years distant. It has two nicknames - Box Nebula and Little Gem Nebula - which both stem from its RGB projection as a rectangular box, seen in this image as the bright white outline. At least two other PN are also nicknamed the Box Nebula - NGC 6309 and NGC IC 4406.

The overall structure of this nebula is very similar to that of NGC 40. Like NGC 40, the white box is the cross-section of the torus of dense material which originally contained the bi-polar PN gas outflow. Our perspective is at 90 degrees, a side view. Also like NGC 40, the gas flow has burst through the ends and expanded into a butterfly shape. NGC 40 is a multi-polar PN and so is this one, as seen by the various axes of gas outflows. A recent scientific study has concluded that this is a quadrupolar PN, but it looks like a bit more than that to me.

The globular cluster NGC 6440 lies 6x further away, at 24,000 light-years distant. The orange tint is very interesting, presumably from a significant amount of dust in that distant direction. The outer extent of the cluster is very unsymmetric, with a void area seen on the left side of the cluster. Again, I assume that this is due to dust.

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