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Perseus Galaxy Cluster

Approx. area of sky captured in image.

Information...

The Perseus Cluster which is located about 240 million light years away, is one of the most massive objects in the known universe. It contains thousands of galaxies, of which 163 can be identified in the above picture. The galaxy cluster is also immersed within a cloud of extremely hot gas, at temperatures in the millions of degrees range, and consequently emits a large amount of X-rays.

Measurements from the NASA's Chandra X-ray observatory & radio observations show that there is a wave in the gas about twice the size of the Milky Way galaxy. The wave was formed billions of years ago by a close encounter with a smaller galaxy cluster. For more info see the NASA website.

For a closer look at the galaxies, use the full resolution image on the Magnifier page.

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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