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NGC6960/6992/6979 - Veil Nebula

(James Clark)

Information...

This is a 2 panel mosaic of NGC6960 aka the Veil nebula, which has been rendered in the HOO palette.

The image was taken with a mono camera fitted with narrow band filters which only allow light from Hydrogen (Hα at 656.3nm) or doubly ionised Oxygen (OIII at 500.7 & 495.9nm) to pass through. In the HOO palette, the light from the Hydrogen emission line is mapped to the 'Red' channel, and the lower wavelength Oxygen to both the 'Green' and 'Blue' channels.

Compared to regular One-Shot-Colour images, the use of the narrow band filters & with a mono camera, and the choice of the HOO palette, helps to really bring out the detail in the nebula. The image is made by pointing the telescope at two adjacent regions of space which overlap by 10-15% and then combining the aligned data into a single mosaic image.

Total exposure time was approx 9 hours, with different times being used in each mosaic panel for the Hydrogen (Hα) and Oxygen (OIII). Individual filter/pane times varied between 80 mins to 2.5 hours.

 

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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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