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NGC6946 - Fireworks Galaxy

(09/09/2020)
(04/11/2021)

Information...

NGC6946 - the Fireworks Galaxy, is an intermediate spiral galaxy which gets its name from the relatively frequent super novae that have been observed in it's arms. (Ten have been observed in the last century, with the latest discovered in 2017 by an amateur astronomer in Utah)

The Galaxy is about 25 million light-years from Earth and has an apparent magnitude of 9.6.

For more info. see the Wikipedia entry.

PS: incidentally, the first image above from 9th Sept 2020 was taken exactly 222 years to the day after it was discovery by William Herschel on 9th Sept. 1798. Unfortunately high cloud truncated our imaging session that night so we didn't collect as much data as we would have liked...

 

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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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