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NGC185

(Cropped close-up)
(Extragalactic Globular Clusters)

Information...

NGC185 is a dwarf spheroidal galaxy approx 2 million light years from Earth in the constellation of Cassiopiea. It is one of at least 13 dwarf satellite galaxies which orbit the Andromeda Galaxy - M31 and is unusual as it has an active galactic nucleus (AGN), a compact region of new star formation in it's centre.

The total luminosity of the galaxy is approx. 8 million times that of the Sun. Most of the stars are also very old, with 70% having being formed over 12.5 billion years ago.

As with nearly all of earth-bound astro-photo's the stars visible in the picture are foreground stars from our own Milky Way galaxy, however in the extreme close-up image a handful of NI185's globular star clusters can be identified.

For more info. see the Wikipedia entry.

 

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Map

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Measuring Angles

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!)

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Apparent Magnitude

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.

Apparent magnitude

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.

 

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