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M42 and the Harvard Computers

This post deals about Orion constellation, and more precisely about M42, the 42nd object Charles Messier integrated in his catalog (see previous post about M31), in 1769.

What is M42?

To do it simple, M42 is a nebula: an interstellar cloud of gases and dust. Those two elements interact with the light emitted by stars in formation at its center.

On one hand the 2 000 000°C gases are ionized by light and, on the other hand, dust reflects or absorbs it.

How can we find it ?

M42 is situated in the Orion constellation and, as M31, it is, without light pollution, visible with the naked eye or with binoculars: its apparent magnitude is 4 (see post about M31).

About 1 430 light years distant, this object is approximately 30 light years across, and if we could see it properly, it would take in our sky a space apparently 4 times larger than the Moon.

You first need to spot the 3 aligned stars that compose the 'belt' of Orion (circled in green on the picture below). To be sure you don't mistake them, check they are surrounded by 4 very bright stars and that in the belt alignment, there is the brightest star of the sky: Sirius.

Now, under the belt, find 3 smaller objects: the middle one pointed in blue is M42.

The picture

This processed picture was taken in Guérande, France in december 2014.

As M31, the Orion nebula requires long time exposure so the sensor can receive enough 'information'. This picture is the combination of 2*15 seconds and 3*20 seconds exposure time (a total of 1'30 exposure time), taken with a Canon EOS 70D, ISO 800, mounted on a Celestron C8 2000mm f/10.

The beginning of astrophotography

In 1875, Edward Pickering, director of the Harvard College Observatory, surrounded by brilliant male students, decided to use astrophotography to classify stars depending on their spectra: once the picture was taken, the job consisted in analysing the photosensitive plates. This is the first photograph of the Nebula's center taken by Professor Henry Draper in 1880. (Source :

Unsatisfied by the work of his students, he decided to give the hard and thankless task to his maid: Williamina Fleming.

In 1881, Williamina started as a calculator and, step by step, learned astronomy. In 1888, she had not only discovered the 'Horsehead Nebula' (which is also part of Orion constellation), but also 58 other nebulae and more than 300 stars!

The Harvard Computers and the 'harem effect'

Edward realised that women were more patient and precise to process such datas. As astrophotography increased considerably the amount of astronomical data to be processed, he decided to hire more of them. This group, leaded by Williamina, came to be known as the "Pickering's harem" or the "Harvard Computers".

The "Pickering's harem". Source :

Let's be honest, Edward was not only interested by the work quality of his female staff, but also in the fact he could pay them twice less than its male staff, and also that they were less threatening to him than an equal number of bright young men.

The Harvard Computers have discovered a lot and have permitted to establish a new way to classify stars, but they didn't receive the credit for it.

All of this happened during the late 1890s and it later became a typical sociological case called the 'harem effect' (different from the human sexual behavior one).

To conclude

In 1906, the Royal Astronomical Society elected Williamina Fleming to its organization: it was the first time they admitted an American woman. She died in 1911, and a lunar crater was named for her (and jointly for Alexander Fleming).

Check out the Hubble website for stunning pictures, and read this for more infos about Harvard Computers.

And try to look up next time nightsky is clear enough, you will maybe spot M42!

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