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M33 - Triangulum Galaxy

(Ivor Trueman)
(James Clark - 2021)
(James Clark - 2023 with added Hα)
(Ray Emery)
(Ivor Trueman)
Cropped & Rotated close-up (Ivor Trueman)

Information...

The Triangulum Galaxy (Messier M33) is a flocculent spiral galaxy approximately 2.73 million light-years away from Earth. The third largest galaxy in our local group (after M31 - the Andromeda Galaxy & the Milky Way), it is estimated to contain approx 40 billion stars (about a tenth of that in our own Milky Way galaxy).

In the past M33 is thought to have interacted with M31, with a 'bridge' of hydrogen gas being detected between the two.

The Galaxy also has several large HII regions of ionised Hydrogen, which appear as bright red spots in the spiral arms, and contain stellar nurseries with high rates of new star formation.

For more info. see the Wikipedia entry. Also see James Clark's Astrobin page for a higher resolution version of his 2023 image.

 

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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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