<FCFORMSHEADER>
<?xml version="1.0"?>

<!DOCTYPE FIRSTCLASS SYSTEM "firstclass.dtd">

<firstclass>

	<fcobject objtype="oConfItem" formid="141" objname="Andy Norton">

		<field id="8018" index="0" type="number">23032</field>

		<subject index="0" >Re: THIRD TARGET - GLOBULAR CLUSTER M3</subject>

		<tonames index="0" >S194 06E real time observing</tonames>

		<tonames index="1" ></tonames>

		<ccnames index="0" ></ccnames>

		<bccnames index="0" ></bccnames>

	</fcobject>

</firstclass>

</FCFORMSHEADER>
OK - here's the colour magnitude diagram of the globular cluster M3.

I measured the brightness of about 30 stars round the edge of the cluster.
Those in the centre are too close together to measure properly.

I measured their brightness relative to a star of known brightness (see image)
and then worked out the magnitudes of my target stars relative to this.

Since all stars in M3 are at rougly the same distance from us, their apparent
brightness is a good measure of their intrinsic luminosity, and their colour,defined as B magnitude minus V magnitude, is a measure of their temperature,

So, stars with a smaller V value are brighter (that's how astronomical magnitudes work!)
and stars with a smaller B-V value are bluer (and therefore hotter).

The colour magnitude diagram of M3 -attached in the spreadsheet - shows that for these stars, the brighter ones are redder (cooler), the fainter ones are bluer (hotter).
What we're seeing in fact is the Red Giant branch. The fainter main sequence
stars in this cluster are all too faint to see.

Andy