Astronomy Now - January 2021

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Owen Brazell

Deep sky challenge: NGC 1999 Orion Nebula’s

peculiar nebulous neighbour

lthough it is always tempting to focus on the great Orion 69 Nebula (Messier 42), there are

numerous other nebulae BL in the area that are well-worth looking at.

e peculiar reection nebula NGC 1999 was discovered by William Herschel in 1785 and he added
it to his class IV objects (planetary nebulae). Later observations showed that NGC 1999 is in fact a
reection nebula being illuminated by V380 Ori, a bright young star of around 3.5 solar masses that
is just 7h 7 75 starting to shine. NGC 1999 is visible by reected light from this star, which appears
bluish owing to V380 Ori’s high temperature of about 10, 000 degrees.

What makes NGC 1999 somewhat odd is a dark patch seen at its centre. Up until about 2010, this
was thought to be an obscuring patch of dust and, if you read the description of it in Steven
O’Meara’s Hidden Treasures book (it is number 33), published in 2007, then it is described there as
such. However, in 2010, the Herschel Infra-red satellite was turned towards it and no emissions were
detected from the dark area. is was followed up by submillimetre observations with the Atacama
Pathnder (APEX) telescope, which also failed to pick up anything.

e dark patch is now thought to be a hole in the cloud, punched out perhaps by a jet from a newly
formed star. e hole could also have been cleared out by radiation from a nearby massive star. is
is a prime example of how observations in different wavebands can change our understanding of an
object.

e region around NGC 1999 is where the rst Herbig–Haro objects were found. ese are the bow
shocks that form when jets from newly formed stars impact on the surrounding interstellar material.
ere is a nice Hubble image of this nebula at
http://www.esa.int/ESA_Multimedia/Images/2017/10/Reection_nebula_NGC_1999.

Observationally, NGC 1999 should be visible as a faint circular patch with a central star through a
200mm (eight-inch) telescope. However, you’ll need a larger aperture and steady seeing to see the
dark patch. I have seen this T-shaped hole once with a 500mm (20-inch) telescope under good skies,
though I suspect that it should be visible through a 400mm (16-inch) aperture. Much larger
instruments show more structure in the hole; see the observations described on-line at the Deep-Sky
Forum’s website at http://www.deepskyforum.com/showthread.php?277-Object-of-the-Week-December-
30-2012-NGC-1999 and-the-quot-Key-Hole-quot

I have not seen any visual observations of the Herbig–Haro objects, but I am sure there are some
using large telescopes. NGC 1999 is a reection nebula, so lters will not help when observing it,
though it is possible that an H-beta lter may reveal the Herbig–Haro objects. NGC 1999 is in the
Astronomical League’s H400 list.

NGC 1999 is a pretty reection nebula in Orion that should be visible through a 200mm (eight-inch) telescope. The curious T-shaped
dark nebula at its centre, well seen here, will require a larger telescope to reveal it.

NGC 1999 is a pretty reection nebula in Orion, sporting a tougher-to-see dark nebula at its

centre, writes Owen Brazell.

NGC 1999 is easy to nd as it is located just 1.3 degrees south-south-east of the mighty Orion Nebula (Messier 42).

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Deep sky challenge: NGC 1999 O...

January 2021

Astronomy Now