Leeds Astronomical Society LAS Meetings Observing Membership

 

 

M94 - Croc's Eye Galaxy

(Cropped close-up)

Information...

M94, sometimes nicknamed the "Croc's Eye Galaxy", is an unusal double-ringed spiral galaxy in the constellation of Canes Venatici. The inner ring with a diameter of about 5,400 light years, is a site of strong star formation, which is driven by gas forced into the ring by the galaxies inner oval-bar like structure. The much fainter outer ring has a diameter of about 45,000 light years and contains approx 23-25% of the galaxy mass & forms approx 10% of the new star formation. The outer ring has recently been shown to be a continuation of the galaxies spiral arms.

In 2008 a study showed that M94 may have very little, if any, dark matter.

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.