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M102 - Spindle Galaxy

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Information...

M102 - the Spindle Galaxy is a relatively bright edge-on lenticular or spiral galaxy 44 million light years away in the constellation of Draco. It is notable for the extended dust disk which is unusual for lenticular galaxies. Pierre Méchain discovered the galaxy in 1781, but he removed it from the Messier catalog two years later as he thought he'd confused it with M101. It has subsequently been reinstated in the Messier list and is also classified as NGC5866 in the 'New General Catalogue'.

Studies of the orbital velocities of the globular clusters in this galaxy suggest that dark matter only account for 35-45% of it's mass, which is small in comparison to other galaxies.

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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