Leeds Astronomical Society LAS Meetings Observing Membership

 

 

M84/M86 - Markarian's Chain

(James Clark)
(James Clark)
(Ivor Trueman)
(Ivor Trueman)

Information...

Markarian's Chain consists of a sequence of galaxies which form part of the Virgo Cluster. Two of the larger galaxies were discovered by Charles Messier in 1781 and added to his 'non-comet' catalogue as M84 and M86.

Also in James' widefield image are M87 & M88. For a close-up of these and numerous PGC galaxies see the Magnifier page.

The Virgo Cluster is a large cluster of galaxies centred about 54 million light years away from the Milky Way.

For more info. see the Wikipedia entry.

 

×

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.