NGC6503 is 18 million light years away and about a third of the size of the Milky Way. The 'Lost In Space' nickname presumably hasn't anything to do with the '60s US TV Show, but relates to its location at the edge of "a strangely empty patch of space called the Local Void", and it's lack of galactic neighbours... The void is at least 150 million light years across.
Hold your arm at full length, then close one eye & use the hand shapes shown above to measure the angular distance between the stars.
(Ain't anatomy wonderful!)
The apparent magnitude of a star is a measure of how bright it appears from Earth. The scale was introduced over 2,000 years ago by the Greek astronomer Hipparchus, who grouped stars into six categories. The brightest 20 or so were deemed to be 'first magnitude', slightly dimmer stars 'second magnitude', and so on until the barely visible stars were classed as 'sixth magnitude'.
Later it was recognised that our eyesight, once it has been given time to get used to darkness, has a logarithmic response. i.e. a Mag. 1 star is actually 2.512 times brighter than a Mag. 2 star, or 6.310 times brighter than a Mag. 3 star (2.512 x 2.512 = 6.310).
The six Magnitudes thus corresponds to a 2.5126 difference in brightness or 100x.
Today the scale has now been extended, so that brighter objects can have an apparent magnitude of 0 or even negative. The brightest star Sirius, for example, has an apparent magnitude of -1.44 and the Sun is a whopping -26.74, due to it's close proximity to Earth.
