Stellar Spectra

I've mentioned previously that the British Library has put over a million images into the public domain. That's a lot of images and there are some real gems amongst them. Today, via @benosteen I saw this image of stellar spectra from 1866.

Stellar spectra
Spectres Sideraux: 1) Soleil [Sun]; 2) α Orion [Betelgeuse]; 3) Aldebaran; 4) Sirius; 5) Rigel; 6) Pollux; 7) Nebuleuse d'Orion [Orion Nebula, M42]. Image taken from page 89 of 'L'Espace céleste et la nature tropicale, description physique de l'univers ... préface de M. Babinet, dessins de Yan' Dargent' CREDIT: The British Library

Although the Sun's light looks mostly white, Newton had shown that it was actually composed of all the colours of the rainbow - the spectrum. With better prisms you can see that it isn't composed of every colour; some specific colours are 'missing' from the solar spectrum and show up as narrow, dark bands. The exact wavelengths of these dark bands are due to the energy levels of specific elements in the atmosphere of the Sun and so act as a chemical fingerprint telling us what the Sun is made of.

Spectra like those shown above were first observed in 1802 by William Wollaston and the dark bands were later named "Fraunhofer lines" after German physicist Joseph von Fraunhofer. By the time this image was published (1866) they'd been known about for around half a century but had not given up all their secrets just yet. Two years later, more precise spectra of the Sun's chromosphere by Pierre Janssen and Norman Lockyer would show a yellow line with a wavelength of 587.49 nm (just next to the sodium 'D' lines) that could not be explained by any of the chemical elements known at the time. Those observations led to the discovery of the element Helium which was later named after Helios - the god of the Sun - due to the method of its discovery.

Like the Sun, other stars show dark lines in their spectra too. This stellar spectroscopy tells you a wealth of information. Not only can you tell which chemicals are present, but also their relative amounts, the star's magnetic fields and the star's history. These days we observe spectra across most of the electromagnetic spectrum from radio waves to X-rays and for a whole variety of objects. As a result we've discovered water, complex hydrocarbons, buckyballs, and even alcohol in space.

Posted in astro blog by Stuart on Thursday 30th Jan 2014 (14:26 GMT) | Permalink

The Old Astronomer

This morning I received a letter from my aunt in Canada. In it she included an extract from a poem by Sarah Williams (1841-1868) set to music composed by Haydn (1732-1809). The poem was "The Old Astronomer" - which I hadn't seen before - and it contains some lovely lines. I've included the full poem here.

Reach me down my Tycho Brahe, -- I would know him when we meet,
When I share my later science, sitting humbly at his feet;
He may know the law of all things, yet be ignorant of how
We are working to completion, working on from then till now.

Pray, remember, that I leave you all my theory complete,
Lacking only certain data, for your adding as is meet;
And remember, men will scorn it, 'tis original and true,
And the obloquy of newness may fall bitterly on you.

But, my pupil, as my pupil you have learnt the worth of scorn;
You have laughed with me at pity, we have joyed to be forlorn;
What, for us, are all distractions of men's fellowship and smiles?
What, for us, the goddess Pleasure, with her meretricious wiles?

You may tell that German college that their honour comes too late.
But they must not waste repentance on the grizzly savant's fate;
Though my soul may set in darkness, it will rise in perfect light;
I have loved the stars too truly to be fearful of the night.

What, my boy, you are not weeping? You should save your eyes for sight;
You will need them, mine observer, yet for many another night.
I leave none but you, my pupil, unto whom my plans are known.
You "have none but me," you murmur, and I "leave you quite alone"?

Well then, kiss me, -- since my mother left her blessing on my brow,
There has been a something wanting in my nature until now;
I can dimly comprehend it, -- that I might have been more kind,
Might have cherished you more wisely, as the one I leave behind.

I "have never failed in kindness"? No, we lived too high for strife, --
Calmest coldness was the error which has crept into our life;
But your spirit is untainted, I can dedicate you still
To the service of our science: you will further it? you will!

There are certain calculations I should like to make with you,
To be sure that your deductions will be logical and true;
And remember, "Patience, Patience," is the watchword of a sage,
Not to-day nor yet to-morrow can complete a perfect age.

I have sworn, like Tycho Brahe, that a greater man may reap;
But if none should do my reaping, 'twill disturb me in my sleep.
So be careful and be faithful, though, like me, you leave no name;
See, my boy, that nothing turn you to the mere pursuit of fame.

I must say Good-bye, my pupil, for I cannot longer speak;
Draw the curtain back for Venus, ere my vision grows too weak:
It is strange the pearly planet should look red as fiery Mars, --
God will mercifully guide me on my way amongst the stars.

Posted in astro blog by Stuart on Wednesday 08th Jan 2014 (12:53 GMT) | Permalink

Earthrise 1896/1968/2013

I've been perusing the British Library's release of 1 million images into the public domain. Amongst them I found an artist's impression of the view of Earth from the Moon published in "The Half Hour Library of Travel, Nature and Science for youngreaders" (1896). What struck me was the similarity with Apollo 8's famous "Earthrise" images taken in December 1968.

Earthrise 1896/1968
Comparison of an artists impression from 1896 with Earthrise from Apollo 8 in 1968 CREDIT: British Library/NASA

Apollo 8's Earthrise images weren't planned and only happened because the spacecraft rolled around at the right time. In December 2013, on the 45th anniversary, NASA Goddard released this wonderful video re-creating how the Earthrise images happened using original images/audio as well as new data from Lunar Reconnaissance Orbiter. It really makes you feel like you were there.

Posted in astro blog by Stuart on Monday 06th Jan 2014 (13:04 GMT) | Permalink

Fake New Year 2014

Last year I wrote a blog post debunking a picture claiming to be the view of Europe from space "at midnight" on New Year's Eve. The image doesn't show that. What it does show are changes in light between 1993-2003 and comes from the NOAA.

Faked satellite image
Not the view at midnight. CREDIT: NASA/NOAA
Encouragingly, quite a few people on Twitter have been on the ball enough to spot some of the clues to why this isn't "Europe at midnight on New Year's Eve". Here are just four:
  1. The image covers over 4 time zones so "Europe" has midnight at different times not all at once.
  2. There are no clouds. A quick check of the weather shows that the entire continent was not cloud free.
  3. Ireland doesn't just have red fireworks.
  4. Highly flammable North Sea oil rigs aren't the best setting for massive fireworks displays.
As expected, the false claim has been doing the rounds again this year only it seems to have come back stronger. Amongst some of the larger culprits this year seem to be: Belgian news site's Facebook post (liked over 300,000 times), @GoogleEarthPics's tweet (retweeted over 2800 times), and @Fascinatingpics's tweet (retweeted over 6,400 times).

Although the image isn't New Year's Eve, what it does show is pretty interesting. Red areas are lights that are new in the period 1993-2003. Blue areas are those that have reduced. Orange and yellow are areas of high intensity lighting that have got brighter.

The original NOAA site hosting the image is currently down (WaybackMachine version). I've emailed them to ask them what is happening with that. I've also contacted and @GoogleEarthPics asking them to issue corrections. Apparently the image has been published in large Belgian newspapers. I'm half expecting the UK's national press to start repeating the claim too. Whatever happens, the likelihood is this is now an annoying annual fixture just like the false "Mars bigger than the Moon" thing every August.

Update 2 Jan 2014 14:05: It seems @GoogleEarthPics replied to my email at 02:32 GMT. Their response was:


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Posted in astro blog by Stuart on Thursday 02nd Jan 2014 (01:59 GMT) | Permalink
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