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Everything posted by toml42

  1. Those are wonderful pictures! I too prefer the darker one, more contrasty. What mount / tracking system are you using, out of interest?
  2. thanks, for the time being i'll be running the 200p ota on a home made dobsonian base, so i imagine the relatively narrow FOV on an ortho would be a disadvantage for a (relative) newbie? do many EPs like this sell on the buy/sell section of this forum? i may wait until i have the required post count to view it
  3. wonderful, thanks! did you buy from an ebay shop, or was it a one off thing?
  4. ha ha, don't forget Big Rip, my personal favourite potential death of the universe, lol
  5. I'll soon be buying my first serious scope, a skywatcher explorer 200p, should be a pleasant jump up from my 3" budget newt! I'm looking to buy a nice planetary eyepiece to go with it, but as i understand it, faster scopes can be a little fussy with the quality/design of their eyepieces. after reading some of the useful primers here, I believe i should be looking for something in the range of ~ 6-8 mm for use with a 2x barlow, as this should give a sensible exit pupil and gives magnification in the range of 250-300, which should be suitable for planetary work with decent seeing. am i on the right lines here? is there anything i should stay clear from, provided i'm at f5, and does anyone have any recommendations? my budget maxes out at about £50 cheers, Tom
  6. The only apparent alternative to expansion theory, is to say that the redshift is caused by every galaxy flying away from us at absurd speeds. The problem is, it turns out that the expansion of space is not linear or even slowing down, as one might expect (it was thought for a long time that the gravity of objects in the universe should be slowing the expansion down), it's actually accelerating. This was observed by comparing the redshift with more conventional means of measuring distance. This means, helpfully, that the Hubble constant describing the expansion is not a constant, and varies with time. This is a big problem in cosmology, and has required the introduction of a repulsive 'dark energy' which would have to make up 74% of the universes mass/energy density and have negative pressure to account for the observations.
  7. ha ha, i like that, reminds me of the different stages of science education i've been through. when i got to uni, the first thing they told us was "ok, so pretty much everything you know is wrong..."
  8. I was not aware of this, do you mean as part of globular clusters?
  9. 1. hard to be specific when none of your criteria are fixed - how big would you like the moons to be, or at least how big visually compared to our moon? I'm sure we can work something out from there 2./3. have a look at the moon systems of jupiter or saturn, i suggest you download the free software 'celestia' and have a play, really helps to visualise some of this stuff. What you would probably find, as you do with jovian/saturnian moon systems, is that they could well form a resonance, this is a nice stable configuration. in other words, their orbits sync up, so for example, every 3 times moon one orbits the planet, moon two orbits twice, what's called a 3/2 resonance - other combinations are possible. this would make a great calendar system for your guys on the surface also, look up 'hill sphere' on wiki, because if you set up your orbits wrong, the small moon might actually prefer to orbit the big moon, instead of orbiting the planet! now that would be cool in itself, but i don't think it's what you're after! 4. 42 astrologer? i don't think i'm familiar with the term...
  10. indeed there are, it would be a lonely existence indeed, i wonder how it would affect the culture and scientific progression of any culture that happened to be orbiting such a star? whilst i do not believe it has ever been directly observed, as resolving individual stars is next to impossible on all but the closest of galaxies, swathes of stars are likely catapulted into the blackness of intergalactic space when galaxies collide, and this happens relatively often. there are also several known 'hyper velocity stars' in the milky way in the process of leaving us, it has been hypothesised they were flung out by a black hole. Milky Way's fastest stars may be immigrants - space - 14 October 2008 - New Scientist also, stars have also recently been spotted forming in gas jets outside their parent galaxy NASA - 'Orphan' Stars Found in Long Galaxy Tail
  11. Wonderful isn't it you may have seen these before, but i thought i'd highlight these rather beautiful forming planetary systems in the orion nebula. It changes the way i look at it though a scope, that's for sure. to think, hundreds of forming solar systems captured in an eyepiece... Born in beauty: proplyds in the Orion Nebula | Press Releases | spacetelescope.org
  12. I really think the term 'Big Bang' should be outlawed. as should the term 'God Particle'. They're terrible descriptions of what's going on, and lead to many misinterpretations and flawed conceptions. "how can nothing explode?" "scientists are trying to find a particle to prove God exists..." 'sigh' easily avoidable. people are just suckers for dramatic names, i guess, lol. I think someone else may already have mentioned this, but let me expand (pun not intended): Imagine an ant on the surface of a balloon that's being inflated. he has two friends, one initially sitting 1 cm away, the other at 10 cm. The balloon stretches evenly, lets say it has doubled in size after 1 second. thus, the ant sitting 1 cm away is now 2 cm away, and the ant sitting 10 cm away is now 20 cm away. as far as our reference ant is concerned, ant one just moved away from him at 1 cm per second, and ant 2 moved away from him at 10 cm per second. but of course, as far as each ant is concerned, he's sitting still, everyone else is moving. if we wait another second, the balloon doubles in size again, ant 1 is at 4cm, apparently now moving 2 cm per second, ant 2 is at 40cm away, apparently moving 20 cm per second, they appear to have accelerated. if we now say that ants can run at 5 cm per second, if sufficiently motivated, and they all start running towards each other out of terror as the balloon begins to inflate, you can see how at short range, they can overcome the expansion and 'collide'. however, the poor fellow at 10cm will never be able to reach anyone, he soon shoots off into the distance. Now, red and blue shifts. I'm sure you're familiar with the doppler effect: the change in pitch as an ambulance whizzes past, for example. you will often be told that this is what causes galaxies to appear redshifted. this is incorrect. well, mostly. doppler shifts are to do with relative motion, and as far as the observers are concerned, for the most part, they are stationary. imagine on our expanding balloon, we were to draw a wave pattern between our two ants, a set number of peaks and troughs that remains constant. as the balloon expands, what changes is the distance between the peaks and troughs, the wavelength, nothing else. now, all light can be understood as waves, shorter wavelengths we perceive as blue, longer wavelengths we see as red. as the balloon, or universe, expands, the wavelengths of the light travelling between the galaxies increases, because the space it is covering is expanding, but the number of peaks and troughs remain constant. The more distant something is, the longer it takes to get to you, so the more time space has to expand. thus, the farther away something is, the redder it appears. now, the doppler effect does also come into play, since galaxies may be moving relative to each other rather than sitting stationary in the expanding universe, but for the most part, this effect is much smaller than that of space expanding, such that it is only really important in relatively close galaxies . it is most noticeable when said nearby galaxy happens to be moving towards us rather fast, so that the doppler blue shift of it moving towards us cancels out the redshift from the expanding space. this is how we know that the andromeda galaxy will collide with our own in a few billion years, should be quite a sight! i realise i may have waffled a bit here, and probably haven't actually answered your questions, but i'd be happy to clarify anything.
  13. actually, it turns out that most of Newtons laws are generalisations of Einsteins. despite being technically wrong, we still use and teach them because for everyday use they're so close to the correct answer that it doesn't matter, and Einsteins equations can be horrendously complicated. I highly expect it's the same case with Einsteins laws. They could be a generalisation of some theory yet undiscovered, yet we'll keep using it regardless, because it's 'good enough' for all but the most extreme cases. maybe if we're lucky, this higher theory will unify Einsteins laws with other branches of physics, that'd be lovely because it would simplify everything a lot! no rule saying it's the case though. and this in turn might be a simplification of some yet higher theory... what keeps me up at night though, is how could we ever know when the succession of generalisations and simplifications ends? does ultimate truth even exist? could we comprehend it? how would we even know when we got there? if our generalised theories get so accurate that we can find no difference, does it even matter?
  14. The short answer is: it depends. The majority of asteroids are moving fast enough that their trajectory is not significantly altered by the Earths gravity. So the main factor is cross sectional area - earth has roughly 13 times the cross sectional area of the moon. for slower asteroids, it's slightly more complicated (the many body problem is ugly), but i would imagine mass would be the deciding factor. you could probably approximate it using the 'Hill spheres' of the Earth and the Moon. (The hill sphere being the sphere where the gravitational influence of the body is greater than the suns influence) it works out for objects at the same distance from the sun to be proportional to the cube root of the mass, which means the earth at 83 times the mass of the moon has a capture radius 4.4 times larger, meaning its capture cross section is nearly 20 times higher. of course, it's probably quite a bit higher than that because these spheres are intersecting but it might do for an approximation.
  15. toml42


    gah, that's a pain, ha ha ha, just my luck... ah well, i understand the reasoning behind it. why didn't i join last week? i'd better get posting then, lol, i'm hoping i can contribute something to the science section as i don't yet have a huge degree of observing experience. cheers for the welcome guys!
  16. just to expand on a couple of points, venus likely has no magnetic field for 2 reasons: 1. Very slow rotation rate. as you probably know, venus takes 243 days to rotate once. the 'dynamo effect' thought to be the cause of planetary magnetic fields requires the metal core to be spinning at a decent rate 2. in the earth the dynamo effect is bolstered by plate tectonics and convection currents in the mantle making everything slosh about, venus is not so lucky
  17. We don't currently have any observations of active volcanoes on the surface of Venus, but expect this to change later this year - the japanese space agency has a probe en-route to look for evidence of current vulcanism, my expectation is that they will find some. lookup 'Akatsuki' for more info. The main barrier preventing study of the Venusian surface is that pesky thick atmosphere and its proximity to the sun when viewed from Earth. Akatsuki should be able to make detailed infra-red observations which should settle the debate. As far as we can tell, Venus is of very similar composition to the Earth, and whilst there is evidence of at least past vulcanism, it appears to be of a very different flavour to that on Earth - there seems to be no evidence of plate tectonics, so the volcanoes we have found are not as localised as they are on Earth. This is a big mystery, but one hypothesis is the lack of surface water on venus, that we obviously have in abundance. The idea is that liquid water on earth creates different pressure and compositional 'zones' in the earths crust rather than being homogenous (ocean crust is thinner and denser than continental crust), and the interaction between these different zones gives us plate tectonics. plate tectonics gives us a more active planet than venus, despite our other similarites. perhaps Akatsuki will give us answers this december. science is about asking questions, and yours are good ones. hope this helps
  18. toml42


    Hi, my names Tom and I am currently studying astrophysics at university. I've been reading this forum for a while, and have found it informative and friendly, and as i'm planning to buy my first serious scope within the next few weeks, i figured it was time i joined!
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