651200Aurora3_p1

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                         THE ROYAL ASTRONOMICAL SOCIETY OF CANADA

                      STANDING COMMITTEE ON OBSERVATIONAL ACTIVITIES


                                       AURORA SECTION                        Bulletin No.3


The Starting Covmrittee on Observational Activities is interested in expanding the present
visual survey of aurora borealis (northern lights) in the skies over Canada. Many in-
dividual members of the LA.S.C. are currently reporting their observations of aurora to
their Centres and to the National Research Council Aurora Survey. Two Centres, Edmonton
and Montreal, have been carrying out ertensive visual studies of the aurora for many years.
Other programmes of aurora reporting are knarn to exist in the Calgary and Halifax Centres.
More recently sane members of the Hamilton Centre have expressed an interest in beginning
a study of aurora.

At present, the sun-spat activity is at a minimtn as a new eleven-year cycle begins. At
any given station in the mid-latitudes, the number of auroras occurring can be shown to
follow the solar cycle. As the number of sun-spots increases, so does the number of
aurora observed.

For the benefit of those amateur astronomers not familiar with the appearance of the
aurora, some characteristics will be briefly outlined:


BRIGHTNESS: Aurora vary in brightness from WEAK (comparable with the Milky Way) to
            BRIGHT (that of a moonlit cumulus cloud). The majority of aurora seen are
            classified as MEDIUM (with brightness resembling a moonlit cirrus cloud).

COLOUR:     Auroras are usually coloured yellow green; the intensity of colour depends
            on the brightness, the brighter the display the more colour observed. In
            the brightest displays, reddish or violet hues may shown as well as the yellow
            green, and should be noted.

FORM:       Sometimes the aurora appears as a faint GLOW near the northern horizon
            resembling the dawn, except in colour. Cirrus clouds near the northern
            horizon, if illuminated by city lights or moonlight, will tend to be more
            reddish in colour and thus are easily distinguished from aurora.

            Generally higher in the northern sky a HOMOGENEOUS ARC may appear as a thin
            band of light with a diffuse upper edge and a sharply defined lower edge.
            Several such arcs may occur at one time with sane joining at the ends. A
            homogeneous arc may increase in brightness and break into a RATED ARC. For
            long rays, this may resemble a drapery or curtain hanging from overhead
            points in the sky.

            In active displays of aurora, several rayed arcs may appear parallel to One
            another. Waves of motion along the form mq develop in such displays,
            folding and unfolding as these waves move along the length of arc. The
            brightest part of the arc may drift slady or rapidly east or west, or
            alternate in direction rapidly.

            Bundles or patches of isolated RAYS accanpany many displays or aurora,
            resembling a searchlight beam in a dusty atmosphere and mixed in with other
            auroral forms.