IC 4685


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IC 4685 is an often overlooked emission nebula. It lies in the same area as the Lagoon Nebula, M8 (located less than one degree west of it), and the Trifid Nebula, M20. These partners are famous enough to quickly and predominantly catch the astrophotographers’ attention. This nebula is attractive for many reasons. One of them is the difficulty of getting a good reproduction of the nebula in narrowband. This is mostly due to the presence of a remarkably beautiful and faint blue reflection nebula. Another reason is the conspicuous presence, as in M20, of three nebula types: emission, reflection and dark nebulas. This image contains several objects. On top of the image is the reflection nebula IC 1274, just left of the 8th magnitude star HD 165999 (the brightest in this image). Just below IC 1274 you can find a blob of emission red nebula, IC 1275. IC 4685 is the larger region in the center, which is crossed by the dark “river” B303. The bright red nebula on the left (East) is NGC 6559, topped by a blue reflection patch that gives it the appearance of a colorful cosmic flower. In order to capture the reflection nebulas, broadband blue images were taken and blended together with the OIII and Halpha narrowband images. The narrowband images account for the amount of detail that can be seen, especially in IC 4685 and the “river” area.

Additional Information


Name(s): IC 4685

Type: Emission/Reflection Nebula

RA:  18h 09m 24s

Dec: -23ΒΊ 58’ 58”

Constellation: Sagittarius

Size (arcmin): 70×50

Magnitude: +7.2

Distance: 4,000 ly


Date: 2016-05-18 thru 2016-06-15

Location: iTelescope.net, SSO near Coonabarabran, NSW Australia

Size (arcmin): 35×35

Telescope: Planewave CDK 20” f/6.8

Camera: SBIG STX16803 (4096x4096pix)

Guiding: Astrodon MonsterMOAG off-axis guider

Total exposure: 16.5 hours (Ha: 5.5h; OIII: 5.5h; SII: 2h; B: 2.5h; RGB (stars only): 1.5h)

Processing: CCDStack, Photoshop CC 2016 and PixInsight

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