Friday, 23 March 2018

Summer's Blue PN: NGC3918

Southern summer has the Carina end of the 'Carina-Sagittarius' galaxy arm high overhead. Rich and dusty, it is packed with remarkable nebulae and star-fields. This 'gem' needs some magnification, but is I think the brightest and bluist of any PNe I've seen. No one else sees a central dimmer region! As summer advances we see more and more of this dense galactic arm until mid-winter,  when we gaze toward the MWG core.

Saturday, 20 January 2018

M42 in pencil

This Summer nebula brings to mind 1960's school days - and  first views with a friend's 4inch 'scope. I took a lot of photos. Yet this 2010 pencil sketch seems more natural - why? The bright stars have been tweaked with software to suggest their dazzling presence. Specs: 10in. F5. H-beta filter, at an urban site.

Planetary Neb in M46

Planetary nebulae are elusive targets - and can be more so if  sited amid bright stars. This one adorns star cluster M46 (NGC2438). Often a narrow-field e.p. helps reduce competing glare. This is a pencil sketch but the stars have been enhanced to show their true sparkle: its a beautiful cluster, but we see just a small part here. The nebula is a chance alignment and the 'central' star is unrelated to it.

Sunday, 5 November 2017

Polarity Inversion Line

Flares fascinate. How and why do these huge high-temperature events erupt? Close study of the polarity of sunspots suggests they occur along the boundary between spots of opposite sign. At least this GOES M4.2 did in AR12673 two months ago. The sketch (lhs) shows the spot group in WL and H-alpha (polarity line in BLUE). The polarity map from the (c)SDO satellite shows the polarity a few hours later. 

Friday, 15 September 2017

X8 Post flare loops

The X8 flare in AR12673 was not seen - with the group now just behind the limb. But the coronal loops acted as conduits for plasma condensing on them to reach the chromosphere. As the fields changed the loops evolved. "Elegant" was how Zirin ("Astrophysics of the Sun", 1986) described them. 

Sunday, 6 August 2017

LMC Blue Filaments (Dragon unbound!)

This sketch covers a bright field 2 deg. N of LMC centre. The fov is 3 full moons wide and 4 high. It's a big field! The two filaments alpha-alpha and beta-beta are, apparently, anonymous. They are very blue in H-beta. It's presumed they are distorted galactic blue-knots or arms of mainly OB stars. The named features are listed l.h.s. Why did the filaments take this strange shape? They are visible in small binoculars. The 'Dragon's Head' is the only thing with a common (and appropriate) name. The whole looks like an Oriental dragon!

Sunday, 18 June 2017

Nu Scorpii: the 'double double'

The writer has always enjoyed viewing double stars, particularly if they are ‘tight’ ones: that is, close pairs that are hard to separate. Although my ‘scopes are not dedicated to the task, ‘tricks’ like using aperture masks and simple orthoscopic eyepieces will often succeed, though the most important factor is steady seeing, that usually occurs later at night.

A favourite example is the ‘double-double’ Nu Scorpii, aka “Jabbah” (Arabic for the Scorpion’s forehead) close to bright star Beta Sco, refer to star maps (P82, Astron 2017). A ‘double-double’ is a quaternary system with two pairs of stars gravitationally bound in a four-star system. As Agnes Clerke wrote (1905): it is “perhaps the most beautiful quadruple group in the heavens.”