Monday, 11 June 2012

James Dunlop and early Australian Astronomy

"Jamie" Dunlop was the first to catalogue southern "deep sky" objects, ie stars clusters and nebulae - if we don't count Lacaille who mapped some with a tiny half inch telescope! Dunlop used a home-made 9 inch reflector. It's not hard to show he was a superb observer and draughtsman, and his catalogue of 600 southern objects mapped and described in seven months (in 1826) is an extraordinary feat! But why are half of these objects now "missing"?

ASNSW has honoured me with a invitation to deliver a talk: "Dunlop the Draughtsman",  in July, when this and other questions will be discussed. Tracking down "missing" Dunlop objects is an exciting project for amateur astronomers.

The image compares well-known southern galaxy N4945 with Dunlop's sketch of it from almost 200 years earlier - and 4945 is not a bright galaxy! Background image courtesy Johannes Schedler, Panther Observatory.

Friday, 1 June 2012

AR11476 Returns!

AR11476 Returns! A great sunspot group is the product of a much larger region of magnetic polarity - called by some :"activity nests". While sunspots arise only where emerging fields exceed ~1500 gauss and are fairly small, the whole region or "nest" can be huge, ten times larger than the spots. Here we see (SDO EUV 304A) the region that produced 11476 a month ago returning at the sun's NE limb. There are spots here, not seen as the nest saturates the SDO detector. White light will show them well. In the corona above the site there's lots to see: PFL are post flare loops above a sunspot and surges or filaments hover above. As well a large coronal hole has developed 30 deg west of the site (black arrows). Is it involved with the "nest" in any way? How long will the nest last - what will it produce during this transit?
"Activity Nest" is a useful term used by Schrijver and Zwaan in "Solar and Stellar Magnetic Activity" Cambridge Uni. 2008. P142~