Friday, 21 October 2016

Thanks Karen!


Thanks for the great talk Karen! Shoalhaven Astronomers were treated to a feast of solar animations on 21st Oct 2016. The challenges in getting time-lapse of solar transients can be daunting: but Karen succeeded. We watched hard-to-see events unfold in amazement, as 'roos grazed the lawns outside. The low density solar chromosphere is dominated by magnetic fields: matter flows sedately - then abruptly plunges to the surface or 'pops' into space without warning. Incredible physics! A great night.

Sunday, 16 October 2016

NGC1532 'Woomera'

Most galaxies are ‘poker-faced’ – giving little away: featureless ovals with faint nuclei; but some offer a glimpse of a more dramatic existence –when galaxies collide.  One such is N1532 (Dunlop 600) in the constellation of Eridanus, the River.
On first impression this is a big edge-on spiral with, seemingly, two nuclei! Higher power shows a small bright elliptical ‘object’ almost in contact with the edge-on’s nucleus. Are these interacting galaxies? References suggest they are: although there is no extended disc to be seen around the small galaxy, NGC1531. The common name for this galaxy pair is ‘Woomera’, the long thin Aboriginal spear-thrower.
In fact, this object seems to still have the ‘spear’ attached! Repeat viewings showed a thin strand of galaxy ‘arm’- aimed at a nearby field star. The whole scene was much like a ‘Mimi’ art figure from Arnhem Land in Australia’s north (Fig). 

Saturday, 1 October 2016

Enigma: NGC55

This is a large member of the Sculptor Group of galaxies; but what are we seeing? Apparently, an edge-on view, but with the bright core to the W and only a fainter arm to the E? A Gendler image suggests the bright 'cigar' is the central core seen through an outer arm of blue stars. Several small 'knots' are likely OB clusters of activity. A possible stellar central nucleus is arrowed. Reference stars are noted in case we see a super nova! This galaxy is seen well in a 4in 'scope. Is NGC55 a barred spiral with only the E arm visible - the W one hidden from view?

Monday, 29 August 2016

N7009: 'planetary' puzzles

Puzzling things planetaries. They mainly emit H-alpha, OIII and H-beta light: i.e. they are almost pure LRGB sources. Here we contrast a superb HST(c) image with the same image made with zero RED and 50% GREEN. This 'recipe' approximates human visual sensitivity. The result is close to what we in fact see in a 10 inch 'scope. Why cant we see red H-alpha in deep-sky objects? Because our Sun emits little in that band and H-alpha is close to the limit of our sensitivity, while we see blue and green quite well. This is why many planetaries look nothing like their big-scope images. 
The central star (inset) was finally seen by 'blinking' with an orange (i.e. minus blue-green) filter, fully blocking the bright nebula but showing the 11.5 mag star.

Saturday, 30 July 2016

AR12565 and 67: Odd Couple

Two spot groups unusually close together. A fine prominence was seen at the limb on Jul22 with AR’s 12565 and 12567 still 20° from the limb. That prominence was likely the filament recorded 20°W of the groups during their disc transit. While very bright plage was seen sandwiched between the two dominant (p) spots and some arf – no flares were logged; flaring was then steady at GOES B2.

More M-flares! A gale cut short the Jul22/23 session, but M5 and M7 flares erupted just 2hrs and 5hrs later! The latter, a twin peaked event, hosted a rare spray of ejecta, apparently from AR12565(Fig SDO log). The spot duo had attained high activity levels while rounding the limb. A 3hr patrol on Jul23/24 with the duo on the W limb only showed plage, some surges, arf and fragments of a flare loop; but an M2 flare erupted just 4hr later at local sunset, again unseen! 
(Zirin, H "Astrophysics of the Sun" (1986) defines a spray as "the ejecta of flares...spray velocities can be huge, up ro 2000km/sec" . . " as from the muzzle of a gun" p270, 280 298 etc)

Friday, 1 July 2016

N6397: plan ahead!

This globular has impressive stats: second nearest, fourth in Skiff’s list of brightest globulars and has the brightest members. Yet it is unimpressive when first viewed. This may be due to the small bright central cluster of stars, and the fact that the vast halo of 12/13mag stars is hard to see in small scopes. Full resolution seems to need a 12” scope or larger: the halo of faint stars is nearly 30min  arc dia.  It’s huge- almost the Moon’s apparent size: third largest after southern ‘giants’ Omega Cen and 47 Tuc. The sketch overflowed the page as more of the halo came into view! Plan Ahead!

A recent view in Bob S.'s 12" Dob showed what a spectacular thing N6397 is. Extra aperture makes a big difference.

Friday, 3 June 2016

B86: 'Inkspot' a stellar nursery?

B86 is, it seems, involved with cluster N6520: faint threads of dark nebulae seemed to ‘tie’ the cluster to the larger ‘inkspot’; or can the two objects be unrelated? The cluster’s distance is given as ~5000ly (1650 pc) but I found no such data for B86.

Star clusters do form in dark clouds and, once cluster members grow bright enough, their stellar winds blow the remaining dust away: perhaps the 54My old cluster is doing just that – and maybe, in time, another cluster will form inside B86? The fainter tendrils that now envelop the cluster and seem attached to B86 may well be in the process of being dispersed by the O-stars winds. And how do we account for the ‘sharp’ boundary on the west edge of B86 where it aligns with the chain of bright stars there? Are their stellar winds the cause of the sharp boundary? I noted two places where the nebula seemed to extend into the star chain:  Maybe this is happening here as chain-members grow brighter: is the whole of B86 liable to be blown apart and scattered into space in the (stellar) near future?