The Owl, the Pussy-cat and the telescope

The distance of relatively nearby stars can be found by measuring their positional change against the ‘fixed’ stars as the Earth orbits the Sun; and there is a known calibration of distance with brightness for ‘Cephid variable’ stars. But the rest had to wait until technology allowed the spectrum of their light to be analysed in exquisite detail. Then you could classify them: a particular spectral type and the precise characteristics of line-pairs within the spectrum placed them in one or other of the regions in the Hertzsprung-Russell diagram. (This diagram plots data obtained from ‘nearby’ stars, and from it you can read off your star’s ‘absolute’ brightness – see The Sun and Hertzsprung-Russell.) Then, if you also know from observation how bright a star appears here on Earth, you can assume an inverse-square law was at work, and so calculate its distance. A certain wide-eyed and romantically inclined bird knew all this long ago.

The Owl and the Pussy-cat went to sea –
They’d decided to elope.
They took some honey, and plenty of money,
And the Owl took his telescope.
The Owl looked up to a star above,
And sang to a small guitar,
“O lovely Pussy! O Pussy my love,
Just how far away is that star,
That star,
That star?
Just how far away is that star?”

Pussy said to the Owl, “That’s just like a fowl;
I thought we were here to get wed!
They’re so far away, surely no-one can say?”
The Owl clicked his beak, and then said:
“We must sample the light from that star above
And measure how brightly it shines.
Then, using a prism, O Pussy my love,
We can check out its dark spectral lines,
Its lines,
Its lines . . .
We can check out its dark spectral lines.”

A little while later, they’d got all the data;
Then a Piggy-wig watched them, aghast,
As they had a great tussle with Hertzsprung and Russell.
But they got to an answer at last.
“Oh Owl, that was thrilling! But look – that Pig’s willing
To sell you the ring in his nose!”
So, wed by a Turkey (which was shockingly quirky),
They danced by the light of the stars,
The stars,
The stars . . .
They danced by the light of the stars.

[Image: omnilore.org]
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