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M31 - Andromeda Galaxy

(James Clark)
(Ivor Trueman)
(Tony Cook)
(James Clark)

Information...

The Andromeda Galaxy (Messier M31) is a large Spiral galaxy approximately 2.5 million light-years away from Earth. It's estimated to contain approx 1 trillion stars (about twice that of our own Milky Way galaxy) and is the closest major galaxy in our local group.

In the past M31 is thought to have interacted with the nearby M33 Triangulum Galaxy and from spectral analysis is known to be travelling towards us at about 300 km/s. It is due to collide with the Milky Way in 4.5 billion years.

Also in the picture you can see M110 (bottom right) & M32 (middle left), two dwarf elliptical galaxies that are satellites of M31.

M31 has an apparent magnitude of +3.44.

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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