Starry pictures
Testing, Testing 1 2 3
Sunday, February 18, 2007
Wednesday, January 10, 2007
Bad Weather
Well this blog didn't go live, and I've not posted anything for a couple of years !!!
But this is a test post :-)
But this is a test post :-)
Monday, July 19, 2004
The moon today
The Moon is 2 days old today, by which I mean it's 2 days since new moon ("moontool.exe" is a useful tool for calculating this, see my links page). This means we should be able to see it shortly after sunset tonight, weather permitting. It's still a pretty slim crescent (or a "pretty, slim, crescent"?) and tomorrow will be better...
Any decent planetarium program should show the location of the moon. You may want to try "Cartes du Ciel", a very good, free, planetarium & sky mapping program: http://www.stargazing.net/astropc/
Finally, a collegue asked me recently, "Why aren't there any seas on the far side of the moon?" Apart from pointing out that there are a few, I didn't know the answer.
Well, whilst reading Gerald North's "Observing the Moon" on my daily commute this morning, I found it! I paraphrase below:
First you have to know what the Maria and Highlands (the lighter-coloured "rest of the moon") are made of. The highlands are made of light-coloured rock, and form a lunar crust of, on average, 60 km thick. The maria are low-viscosity (ie. runny) basaltic lava that came from under the crust as a result of impacts, filling the basins and large craters caused by the impacts.
The current favourite theory regarding the origin of the moon involves the early Earth being hit by a planet-sized object while it was still in the formation stage. The debris from the impact formed the moon and the modern Earth.
Now due to the less-than-solid (at the time) nature of the rocks involved, gravity played a big part in the formation of the internal structure of the moon. Not only did the moon become rotationally locked to the Earth, so that the same side always faces us, but the gravitational pull between the moon and the Earth affected the bulk of the moon below its crust such that the closer side has a thinner crust. The crust on the far side is 100km thick, while the crust that faces us is only 20km.
The thicker crust of the far side was much less likely to crack and eject lava when the big impacts occurred. Therefore we don't see the large dark areas filled with lava we call seas.
So there you have it!
Actually one mare that is mostly on the far side (we can just see its edge when that side of the moon is tipped towards us) is the Mare Orientale. That is a very impressive bull's-eye like feature: http://antwrp.gsfc.nasa.gov/apod/ap960112.html
I recently read a suggestion to consider what role the moon might have played in our cultural history and superstition if that giant "eye" had been facing the earth for millenia!
Any decent planetarium program should show the location of the moon. You may want to try "Cartes du Ciel", a very good, free, planetarium & sky mapping program: http://www.stargazing.net/astropc/
Finally, a collegue asked me recently, "Why aren't there any seas on the far side of the moon?" Apart from pointing out that there are a few, I didn't know the answer.
Well, whilst reading Gerald North's "Observing the Moon" on my daily commute this morning, I found it! I paraphrase below:
First you have to know what the Maria and Highlands (the lighter-coloured "rest of the moon") are made of. The highlands are made of light-coloured rock, and form a lunar crust of, on average, 60 km thick. The maria are low-viscosity (ie. runny) basaltic lava that came from under the crust as a result of impacts, filling the basins and large craters caused by the impacts.
The current favourite theory regarding the origin of the moon involves the early Earth being hit by a planet-sized object while it was still in the formation stage. The debris from the impact formed the moon and the modern Earth.
Now due to the less-than-solid (at the time) nature of the rocks involved, gravity played a big part in the formation of the internal structure of the moon. Not only did the moon become rotationally locked to the Earth, so that the same side always faces us, but the gravitational pull between the moon and the Earth affected the bulk of the moon below its crust such that the closer side has a thinner crust. The crust on the far side is 100km thick, while the crust that faces us is only 20km.
The thicker crust of the far side was much less likely to crack and eject lava when the big impacts occurred. Therefore we don't see the large dark areas filled with lava we call seas.
So there you have it!
Actually one mare that is mostly on the far side (we can just see its edge when that side of the moon is tipped towards us) is the Mare Orientale. That is a very impressive bull's-eye like feature: http://antwrp.gsfc.nasa.gov/apod/ap960112.html
I recently read a suggestion to consider what role the moon might have played in our cultural history and superstition if that giant "eye" had been facing the earth for millenia!
