Viewing 47 Tucanae from Singapore

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starfinder
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Viewing 47 Tucanae from Singapore

Post by starfinder »

This morning, at around 6am, I managed to view the far-southern globular cluster 47 Tucanae (NGC 104) from my home in central Singapore.

This is I think the second brightest of all globular clusters but is seldom observed from Singapore or Malaysia. This is because it does not rise high above the horizon and is thus often overlooked.

I viewed it through the eyepiece of a fork-mounted 100mm binoculars at around 30x power. The object was located by star-hopping, starting at the bright mag 0.5 star Achernar (alpha Eridani), and then proceeding 10 degrees southwest (right) to the double-star Beta Tucanae (mag 4.3), and then onto Zeta Tucanae (mag 4.2), Epsilon Tucanae (mag 4.5), then south (downwards) to Pi Tucanae (mag 5.5) and then onto 47 Tucanae itself.

47 Tucanae (mag 4.0, 6.3 arcmin diameter) was at about 15.5 degrees above the horizon (due south). It's declination is -72 degrees, and so the highest it ever rises when it culminates and transits the meridian above the southern horizon in Singapore is about 16.5 degrees.

In the eyepiece, 47 Tucanae was distinct. It certainly had the appearance of a globular at 30x. From memory, it's much smaller than Omega Centauri and not as bright overall, but its central core is brighter than Omega's.

I've also devised a quick way to roughly locate 47 Tucanae from Singapore. First, find what I call the Southern Triangle (about 40 degrees length each side), formed by Achernar, Fomalhaut, and Alpha-Pavonis (the Peacock Star). Move about 14 degrees right along a line that runs from Achernar to Alpha-Pavonis, then make an adjacent turn downwards about 9 degrees, and that's roughly where 47 Tucanae is.

Here is an illustrative chart which I've made (annotations over a screenshot from Stellarium). It also shows when this Southern Triangle is high up in our skies, which is also when 47 Tucanae is around its highest.
Image
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Gary
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Re: Viewing 47 Tucanae from Singapore

Post by Gary »

Brilliant! Thanks for sharing your methods.

Another potential agar-agar (estimation) method is this:

(1) Draw a line joining the bright stars Achernar and Alnair.
(2) Mentally splitting this line into quarters (visualise half and then half it again towards Achernar).
(3) From the nearest quarter to Achernar, move down (towards south) perpendicularly for 4 telrad circles.

(sorry, too lazy to do screen capture annotation for now. lol)
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