Leeds Astronomical Society LAS Meetings Observing Membership

 

 

M81 - Bode's Galaxy & M82 - The Cigar Galaxy

(James Clark - Ha/RGB composite)
(M82 - James Clark - Ha/RGB composite)
(James Clark / Clemens Fischer - Integrated Flux nebulae)
(James Clark)
(M81 - James Clark)
(James Clark - 700mm)
(Ivor Trueman - ZWO ASI2600MC-PRO)
(Ivor Trueman - 200dps)
(Ivor Trueman - 130dps with NGC3077)

Information...

M81 - Bode's Galaxy, is a grand design spiral Galaxy about 12 million light-years from Earth and is named after the German astronomer Johann Elert Bode, who discovered it in 1774. It was also the first spiral galaxy in which rotation of it's arms was detected thorugh spectroscopic analysis, when Maximilian Wolf discovered the linear rotational velocity at the edge of the galaxy to be approx. 300 km/s.

It's close neighbour, M82 - the Cigar Galaxy, gets it's name from it's edge-on appearance. It is a Seyfert 'star-burst' galaxy with it's central core being 100 times more luminous that the centre of our Milky Way. Images from Hubble identified 197 young massive clusters in it's core, each with an average mass of 200,000 times that of our Sun. The high rate of star formation is due to gravitational tidal action from M81.

Also within the M81 Group is NGC3077 a small disrupted elliptical galaxy.

For more info. see the Wikipedia entries for M81, M82 and NGC3077.

James Clark's full resolution images & more info can be found on his IFN and M81/M82 Astrobin pages.

 

×

Map

×

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!)

×

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.