Caldwell 78

Globular Cluster in Corona Australis

NGC 6541

Magnitude: +6.3
Apparent size:15 arc min
Diameter:107 light years.
Distance:24,000 light years.

C78 is the twelfth brightest globular cluster in our sky, orbiting the Milky Way at a distance of 24,000 light years from Earth. It is an inner-halo globular, above the central core of the galaxy, about 7,200 light years from the galactic centre. It’s age is quoted as around 13 billion years.

The bright white star (lower left), HD1655199 is magnitude +9.99.

The bright red star (far left), HD165124, is a magnitude 8.01 red giant variable star

Image date:2020-09-15
Exposure:6 x 6 minute sub-frames = 36 minutes.
Field of View:47.8 x 31.7 arcmin; up is 170 degrees E of N.

C78 is located in the sky at about 43° South, so it is visible in both hemispheres. Here are two location maps, generated for me by Astrometry.net:

Grand Conjunction Diary

Time for moan. I had a premonition that the weather outlook was going to be poor in December. It often seems to have been in recent years but with the Grand Conjunction of Jupiter and Saturn set to climax on 21st December, I was certain of a poor weather outlook. I had two opportunities to image the early stages of the event, on the 4th Dec and 6th Dec and I’m glad I took advantage, because since then, as the two planets continued their rare convergence:

7th Dec: 100% cloudy.
8th Dec: 100% cloudy.
9th Dec: 100% cloudy.
10th Dec: 100% cloudy.
11th Dec: 100% cloudy.
12th Dec: 100% cloudy.
13th Dec: 80% cloudy. I would never get my telescope out with 80% cloud cover but – in desperation – I set up and had just picked out the two planets in a break between the clouds and was almost ready to begin imaging, when it began <beeeeeeeeeep>ing raining on my telescope! and I was forced to beat a very hasty <beeeeeeeeeep>ing retreat.
14th Dec: 100% cloudy.
15th Dec: 100% cloudy.
16th – 23rd Dec: The seven day forecast is 70% to 90% chance of rain every day. 🤯
!@#$%$@*!

Telescope Details

SkyWatcher Esprit 120 mm apochromatic 3-element refractor; 840 mm f/l @ f/7.
Field flattener; 2x Televue Powermate. ZWO Duo-band Hα (656nm) and OIII (500nm) filter.
SkyWatcher EQ6-R Pro mount; ZWO ASI120 guide camera.
Imaging camera: ZWO ASI 071 MC Pro (CMOS 28.4mm 16 Mpx).
Software: EQMOD, PHD2, SharpCap, Gimp.
Observatory location: 34° South.

See annotated image at Astrometry.net

Images © Roger Powell

I’m a founder member of Macarthur Astronomical Society

9 Comments

  1. From near New York, New York…. had a bunch a clear-enough-for-planets days, but not so much lately. Tonight may be good. Tomorrow afternoon we have a coastal storm into Thursday. A foot+ of snow possible. Fun fact: Australia is one of the few other places in the world to get storms that ride along the coast like those on the eastern USA coast. (According one of my meteorology courses back from when dinosaurs roamed the earth.)

    Liked by 1 person

    1. Good question. These things depend very much on how the image post-processing is carried out and can often provide some false colours, depending on the camera and the type of filter used in conjunction with it etc.

      In this case, the exposure and processing has produced an image which is probably fairly true to colour. The large red star on the left is definitely identified as a red giant. The other red stars are likely to be a mix of maybe a few more distant red giants, together with a whole lot of nearby red dwarfs, which are the most common stars.

      The red shift of Milky Way stars is insignificant as they are all relatively local. Red shift is principally used to measure the distance of galaxies beyond the milky Way.

      Thanks for asking!

      🌞

      Liked by 2 people

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