The width of the Veil Nebula is 3 fingers

So how does one calculate the width (in degrees) of any distant object – from say the Veil Nebula 2100 light years away to the width (in degrees) of that mountain just 21 miles away? Simple. But you will need a scientific calculator. Here’s one:

English: A wide-field image of the Veil Nebula...
English: A wide-field image of the Veil Nebula, made as a colour composite from individual exposures from the Digitized Sky Survey 2. The field of view is 4.2 x 4.4 degrees. (Photo credit: Wikipedia)

Using the information given to you, say in an article about the Veil Nebula , calculate a ratio of distance over width.

In this case, we are told the Veil Nebula is 2100 light years away and it is 110 light years in width. It is very convenient that they gave us distance and width in the same units (light years), else we’d have to do that ourselves.

So, 2100 / 110 = 19.1

Using your scientific calculator (see above), enter 19.1 and hit the COT function (COTANGENT).

The answer of 5.9 (degrees), or about the width of your three fingers extended at arms length towards the fabulous night sky – in this case in the direction of the Swan Constellation.

Happiness is Astronomy !

(Conversely, of course, if you estimate the distance of an object and also estimate its width (in degrees), then you can determine the approximate width of the object {in feet, miles, light years, etc.}).