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woodblock

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About woodblock

  • Rank
    Star Forming

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  • Gender
    Male
  • Interests
    Painting, Printmaking, Astronomy, Growing Vegetables and Fruit
  • Location
    Shropshire UK
  1. I'm looking into try imaging. I've got a book called Digital SLR Astrophotography by Michael Covington which is an excellent book but there is one thing I'm slightly confused about. Right at the beginning of the book he says that for DSLRs the optimum focal length of the telescope is about 500mm. Which is quite small. For an f5 telescope that would give an objective size of 100mm. I kind of understand the reasons behind the 500mm optimum size which I think is mainly down to resolution. However, if I were to use a telescope with a longer focal length would that make the images worse quality or is it the case that you just don't get any better quality so the longer focal length is effectively 'wasted'. Also why are many of us chasing bigger and bigger objective sizes all the time? Cheers Steve
  2. Hi there, some of the retailers offer the Skywatcher 200pds with the EQ5 Pro mount. But there is also an EQM35 Pro mount which seems to have about the same payload capacity. The skywatcher global website doesn't have many details of the EQM35 mount but I wondered what's to choose between the EQ5 Pro and the EQM35Pro mounts for the same telescope? Cheers Steve
  3. Hi, This was my post. Not sold yet so I'm reducing the price of this scope to £500. Cheers Steve
  4. Skywatcher 350P Dobsonian. (14 inch) Basic manual scope in good condition. Some flocking applied to upper tube otherwise no modifications. Purchased new in 2015 from Rother Valley Optics D=355mm F=1650 10mm and 25mm skwatcher superploesl eyepieces 9x50 finder Astrozap dew cover £800 to be collected. - Shropshire near Shrewsbury
  5. I think that the rocky asteroids were formed from the break up of much larger objects. The biggest asteroids is Ceres which is about 1000km diameter. Most of them are much smaller. Even much smaller ones have craters on them and look pretty solid. I think my idea of a kind of pile of rubble held together by weak gravity is wrong although I suppose there may be some like that.
  6. Thanks, This kind of brings me back to my original point. You say they modelled a collision between a 1km and a 25km asteroid but the result of the collision will depend on how they modelled the composition of the asteroid. My idea was that asteroids of that size would be no more than a aggregation of rubble held together by weak gravity rather than solid rock. It would be easier to break up a pile of rubble than a solid rock. Steve
  7. Thanks Chris, I've ordered the book by Caroline Smith. Looks interesting. Steve
  8. Thank you both. Amongst the pictures I looked at is one on called Ryugu. It's described in Wikipedia as a pile of rubble and it does look very much like that. It's just under a kilometre across so the gravity must be quite small I think. When you look at the photo there are quite a lot of biggish boulders or rocks dotted around on the surface. I wondered if those rocks were part of the original solar system forming dust cloud. If they are, then where did they come from? Did they come from a rocky planet which broke up long before the solar system formed? This asteroid in particular does look like you could break it up with a few hard knocks. This came to me because I saw an article on Universe Today which said that scientists have worked out that you couldn't break up a large asteroid with a nuclear bomb. So tough luck Bruce Willis. Then I thought if they were loose aggregations of dust and rock then they should be easy to break up. I'm surprised that an object as small as 100km diameter would be big enough to cause melting and rock formation but I guess someone's done the maths.
  9. It's been ages since I was here but I have a question about asteroids. I've been looking at some of the brilliant photos of asteroids which are available now. They look really solid. According to Wikipedia asteroids were formed from the original dust and gas clouds when the solar system was formed. It also says that most asteroids are made of rock. So I was wondering how the dust and gas eventually turned into rock. On earth sedimentary rock is formed from deposits of say sand and over time and with lots of pressure it eventually becomes sandstone for example. But I'm guessing that asteroids don't have a lot of gravity so where did the pressure come from to press all this dust into something like rock? One idea I had was that the asteroids were originally part of a planet which was broken up into rocky fragments. But the information I have doesn't say that. I had this idea of an asteroid as a pile of dust held together loosely by it's weak gravity and that if you gave it a good hard knock it would shatter. I think that's wrong so what's wrong with my reasoning? Cheers Steve
  10. The other day I was speaking with someone about how I could adapt my telescope for imaging. I happened to say that my telescope was unguided and he corrected me and said I probably meant undriven. So just to clarify what he meant. A guided scope must also be driven but a driven scope is not necessarily guided. Is that right? My scope is a basic Dobsonian by the way. I had the idea that if you had an equatorial mount all you needed was a drive on the one axis and that it would automatically track a star providing that it was aligned correctly of course. Obviously there are some objects such as the moon and planets where this wouldn't work. What other situations are there where you might need a guided scope? Cheers Steve
  11. Thanks Dave, I have a DSLR. Would I need a tracking mount for the camera? Cheers Steve
  12. I'm thinking this is something I'd like to try but I haven't the kit at the moment. Just a quick technical question. How do you calibrate your measurements? Since each night the atmosphere will be more or less transparent there must be some way of allowing for that. Cheers Steve
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