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M101 - Pinwheel Galaxy

(James Clark 2022 + 2023)
(James Clark 2022 + 2023)
(Ivor Trueman - 2022)
(Ivor Trueman - 2022)
(Ivor Trueman - 2020)
(James Clark - 2022)
(James Clark - 2022)

Information...

Supernova SN 2023ixf in upper outer arm of M101.

M101 - the Pinwheel Galaxy is a large spiral galaxy 21 million light-years from Earth. Approx. 170,000 light-years in diameter, it is home to about 1 trillion stars.

The Galaxy has a high population of HII (ionised hydrogen) regions, which appear as bright red spots in the spiral arms. These are regions of new star formation and are illuminated by extremely bright and hot young stars.

The asymmetry in the spiral arms is due to gravitational interaction with companion galaxies, including NGC5474 which can be seen in the bottom right of the picture. The interaction is also thought to have created the distortion in this dwarf galaxy.

On 19/05/2023 a supernova was discovered in M101 by amateur astronomer Koichi Itagaki. The animation here shows M101 about a fortnight later on the 03/06/2023 from a back garden in Leeds, compared to the previous year.

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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