AR 12536: An unusual bipolar sunspot group

2017 January 22

Peter Meadows

Introduction

During 2016 April and May a highly tilted bipolar sunspot group was observed – quite unusual given that most bipolar groups have the line between the leader and follower sunspots tilted by only a few degrees with respect to the solar equator. Here the observations of this group are described, the confirmation of the bipolar nature of the group is made using magnetograms from the Solar Dynamics Observatory and measurements of the tilt are given. Also the calculation of the tilt and length of the group are provided.

Warning: never look at the Sun with the naked eye or with any optical instrument unless you are familiar with safe solar observing methods.

Observations

Regular white light observations were made using an 80mm refractor on an equatorial mount and the projection method. A projection box is attached to the eyepiece holder so as to form, with a suitable eyepiece, an image of the whole of the solar disk of 6-in (15cm) diameter at the far end of the projection box. Following east-west alignment of a prepared blank disk sheet, sunspots are drawn for subsequent analysis that includes the number of groups, the sunspot number, group classification and group heliographic location. The calculation of the latter is eased considerably using the HelioViewer software tool. Occasional white light images of interesting sunspot groups are taken with a 105mm ETX telescope, Baader N3.8 solar film and an Imaging Source DMK camera.

Appearance

NOAA Active Region (1)2536 was initially seen on 2016 April 26 as a small single sunspot at a heliographic latitude of 14°N and longitude 118°, close to the eastern limb during solar rotation 2176. On the following day two small sunspots had developed towards the south of the penumbral spot. One of these developed further into a small penumbral sunspot of similar size to the northern penumbral spot. Thus AR 2536 had the appearance of a bipolar D group (bipolar with leader and follower sunspots both having penumbra) which was highly tilted with respect to the solar equator (i.e. the line between the leader and follower being at an angle of much more than the usual few degrees)…. (continued)(Login or click above to view the full article in PDF format)