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OpenLearn Live: 15th June 2016

Updated Wednesday, 15th June 2016

The discovery of the moons of Mars. Then more free learning through the day.

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OpenLearn Live links the world of free learning with your world. This page will, technology permitting, be updated during the day.

Yesterday, we tried to make some sense of Orlando and caught up with All In The Mind

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Today's posts

Moon/June: Deimos & Phobos

This week, we're celebrating the worst art of the songwriter by marking the ineffable linking of moons and Junes. Yesterday, we travelled to Charon, Pluto's twin. Today, we're coming a bit closer to home, and making a quick touch down on Deimos and Phobos.

Deimos Copyright free  image Icon Copyright free: NASA/JPL-caltech/University of Arizona

Deimos and Phobos are Mars' two moons. And we know not just about the moment they was discovered - in 1877 - but we also have a fairly detailed description of the discovery of Phobos, by Asaph Hall:

I repeated the examination in the early part of the night of 11th [August 1877], and again found nothing, but trying again some hours later I found a faint object on the following side and a little north of the planet. I had barely time to secure an observation of its position when fog from the River stopped the work. This was at half past two o'clock on the night of the 11th. Cloudy weather intervened for several days.

"On 15 August the weather looking more promising, I slept at the Observatory. The sky cleared off with a thunderstorm at 11 o'clock and the search was resumed. The atmosphere however was in a very bad condition and Mars was so blazing and unsteady that nothing could be seen of the object, which we now know was at that time so near the planet as to be invisible.

"On 16 August the object was found again on the following side of the planet, and the observations of that night showed that it was moving with the planet, and if a satellite, was near one of its elongations. Until this time I had said nothing to anyone at the Observatory of my search for a satellite of Mars, but on leaving the observatory after these observations of the 16th, at about three o'clock in the morning, I told my assistant, George Anderson, to whom I had shown the object, that I thought I had discovered a satellite of Mars. I told him also to keep quiet as I did not wish anything said until the matter was beyond doubt. He said nothing, but the thing was too good to keep and I let it out myself. On 17 August between one and two o'clock, while I was reducing my observations, Professor Newcomb came into my room to eat his lunch and I showed him my measures of the faint object near Mars which proved that it was moving with the planet.

"On 17 August while waiting and watching for the outer moon, the inner one was discovered. The observations of the 17th and 18th put beyond doubt the character of these objects and the discovery was publicly announced by Admiral Rodgers.

So what are these two like? Here's a short introduction:


Their mythological namesakes were twins; Phobos, a personification of fear - and Deimos, the god of terror. Their warlike names inevitable, perhaps, as they circle the planet named for the god of war.

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