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IC2574 - Coddington's Nebula

Cropped close-up

Information...

IC2574 - Coddington's Nebula, is variously described as either an intermediate (SABm) spiral or irregular dwarf galaxy, but whilst it's galaxy class is in dispute there's no question that it is faint! (The above image has a total exposure time of 9 hours 42 mins with a cooled OSC CMOS Astro-camera).

Located in the constellation of Ursa Major, the galaxy is part of the M81 Group, about 12 million light-years from Earth.

It is believed that the galaxy is comprised of 90% dark matter. The brighter spots in the image are regions of new star formation.

The galaxy is named after the American astronomer Edwin Foster Coddington, who discovered the 'nebula' in 1898.

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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