Leeds Astronomical Society LAS Meetings Observing Membership
Pictures Contact Early History Nebula Chatline Light Pollution Links

 

 

NGC2403

(James Clark - RGB + Hα)
(Ivor Trueman)
(Ivor Trueman - Cropped close-up)

Information...

NGC2403 appears as a small faint intermediate spiral galaxy in Camelopardalis, although it is of a similar size to M33. The galaxy forms part of the M81 cluster & is approx 7-8 million light years away.

Edwin Hubble detected Cepheid variable stars within this galaxy, making it the first outside of the local group to have it's distance derived. From observations of the Cepheid, Hubble calculated a distance of 8,000 light years, about a factor of 1000x lower than the accepted distance today.

For more info. see the Wikipedia entry.

James Clark's full resolution image & more info can be found on his astrobin page.

 

×

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.

 

Visit us on Facbook Find us on Instagram Find us on Flickr LAS © . Registered Charity 1101539