[AZ-Observing] Re: NGC 3372 - The Keyhole portion of the Carina Nebula in narrowband
- From: "Bernard Miller" <bgmiller011@xxxxxxx>
- To: <az-observing@xxxxxxxxxxxxx>
- Date: Fri, 31 Aug 2018 13:44:34 -0700
Great information Brian. Thanks for sharing.
From: az-observing-bounce@xxxxxxxxxxxxx <az-observing-bounce@xxxxxxxxxxxxx> On
Behalf Of Brian Skiff
Sent: Friday, August 31, 2018 1:31 PM
Subject: [AZ-Observing] Re: NGC 3372 - The Keyhole portion of the Carina Nebula
On Fri, 2018-08-31 at 12:43 -0700, Bernard Miller wrote:
This is an image of the Keyhole Nebula region of NGC 3372, also known
as the Carina Nebula. The Keyhole Nebula is a dark nebula near the
center of the much larger Carina nebula, which is a complex nebula
about 6,500 light years away in the constellation Carina. This image
was captured with narrowband filters and processed using the Hubble palette.
The bright star in the center is eta Carinae itself, famous from various
HST images. The star is currently at an historically bright level outside of
the famous mid-19th Century eruption, when it was nearly as bright as Sirius.
Using my 15cm refractor from Chile in 1990, I saw the star as distinctly
orange-red, as was its associated 'Homunculus Nebula', which has
extraordinarily high surface brightnesss and is just about the oddest thing I
ever saw in my deep-sky viewing days.
The oval 12"x8" nebula was sharply defined, and having the perfect Airy disc
and single diffraction ring of eta Carinae sitting on top of it was
extraordinary. Alas, those tiny details are absent in Bernard's image, and
they will require much longer focal length and only a few seconds of exposure
In this shot, north is up and east to the left, very nearly.
The small cluster to the northwest of eta Car is Trumpler 14.
Its brightest central star is HD 93129 (about mag 7), known as one of the very
hottest luminous stars, and is actually a close triple. In the refractor this
cluster was very compact with about 30 stars counted at 200x in a 2' area. (So
imagine a cluster slightly larger than the long axis of the Ring Nebula, and
stuff 30 fairly bright stars in it --- there is nothing comparable in the
northern sky.) HD 93129 was resolved as a 3" unequally-bright pair, which was
first measured by John Herschel at the Cape in 1836. The two stars have
spectral types O2If and O3.5V, and help define the very earliest spectral types
for luminous stars.
I found the broad nebula to be rather poor visually using an [OIII]
filter, but the old UHC filter (that includes [OIII] and H-beta emission) or
just no filter much better for general viewing. The 'keyhole' feature just
west of eta Carinae is readily visible at just 30x and 80x in my small
I wrote at the time that this is nearly black at the southern end, and was
filled-in northward but retains a well-defined border; the contrast was
generally improved by the UHC filter.
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