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# Tiki

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416

1. ## Universe expansion

Consider the following thought experiment: We are in a rocket and hover above a test particle located half way between two streams of matter . We notice that the only forces that act upon the particle come from the gravitational influence of the two matter streams. We notice that the two matter streams are composed of identical particles which move with the same speed but in opposite directions. We are able to ascertain that the density of the two matter streams are identical and therefore influence the test particle in equal but opposite ways. It is no surprise that the particle remains at rest in such a symmetrical situation. We now zoom off in the rocket in a big loop and pass by the test particle, however this time we are moving at the same velocity of one of the matter streams. By the symmetry of the situation and the fact that our idealized rocket doesn't interact with the test particle we are again not surprised to see the particle still at rest just as before. Why shouldn't it be? When we whizzed by, we took a whole bunch of measurements. The upshot is that the densities of the matter streams no longer appear to be the same! On our flypast one of the matter streams appeared as a stationary line of particles whilst the other appeared to be composed of particles moving at twice the original speed. The moving particles would appear more dense for two reasons: a slight increase in mass of each particle and because we would measure the distance between particles to be less than in the static stream. (special relativity) Why doesn't the test particle move towards the moving matter stream? Ans: Because there is a pushing force which exactly counters the effects of the increase in density of the moving matter stream.
2. ## The force of gravity

Short answer: because we live in a world of three spatial dimensions. Three minute answer: https://www.youtube.com/watch?v=tmNXKqeUtJM. The link is to a 'minutephysics' youtube clip. Minutephysics have an excellent upbeat style. 'Why is the sky dark at night?' is another good clip.
3. ## M101 observing with 4 inch refractor - no luck

When the transparency is excellent, M101 near the zenith, not even a hint of moon I can just about make out M101 with direct vision using my TV101 from my 'suburban' back garden. For comparison, M31 can just about be observed with direct vision naked-eye with similar positioning/conditions. Sighting M101 (or M31 naked-eye) from home tells me that the conditions are excellent. Once you have memorized the star-fields it could be worth trying a shorter focal length EP (15ish-25ish) in your search. From home especially, I find that higher powers can sometimes help with low-contrast objects by darkening the sky background. Good luck with your search.
4. ## What is "typical" suburban light pollution?

Some more star-count-maps here: http://www.project-nightflight.net/limiting_mag.pdf
5. ## How to make a cloud chamber!

Building a cloud chamber has been one of my 'gonna do' projects for quite a while. A peltier design is outlined here http://www.xionone.co.uk/howtomakeacloudchamber1.htm. There is also a video of such a cloud chamber in action https://www.youtube.com/watch?v=WtsDEkCAS_Q&feature=youtu.be.
6. ## How does diffraction work?

Nice job. I wouldn't worry too much about brightness as it could be just a matter of tweaking the grayscale definition. From Cambridgeincolour: "Gamma ...... defines the relationship between a pixel's numerical value and its actual luminance." http://www.cambridgeincolour.com/tutorials/gamma-correction.htm
7. ## Trouble finding the M101 (Pinwheel galaxy).

Easy to find: Suppose Mizar and Benetnash (eta u.majoris) are diagonally opposite corners of a square. M101 is then on one of the other corners of the same square. It is easy to use a red-dot finder to line up on this spot. From my moderately light polluted garden, I can only ever make out M101 under exceptional conditions: M101 near the zenith, excellent transparency and no moon. In my TV101 it is not much more than a smudge. I always look for it in decent conditions because it is easy to point the scope at and on the odd occasion that I can actually see I know that the conditions are truly top notch. For comparison, if the conditions are exceptional and M31 is near the zenith it is just possible to discern the core with direct vision.
8. ## How does diffraction work?

Not necessarily. Symmetry is your friend. For example, you already have enough data from your cross-section to generate a disc and rings for a refractor (spherically symmetric diffraction artifacts). A 'standard' four spiked Newtonian star will only require 1/8th of the diffraction image calculated. Good luck with your challenge.
9. ## How does diffraction work?

The graphs look good. Have you managed to overcome the resolution/speed issues that you mentioned in an earlier post?
10. ## Gravitational Lensing

Perhaps these gravitational lenses should be thought of as the ultimate cure for aperture fever:)
11. ## Scientific method

If for instance you want to discuss physical science (chemisty, physics, astronomy) on a non-trivial level, then you are going to have to use an appropriate language. ie. maths. All other languages are less efficient. Unlike spoken/written languages, maths has it's own built in logic/rules and disaster ensues should you break any of them. It is possible to use bad grammar in English (for example) and not sacrifice meaning. Logically fallacious statements can also be grammatically correct in spoken/written language. I believe maths to be a language, it just that certain 'sentences' can be precluded. Maths can be descriptive which makes it more than just a grammar. How does one describe an electron with words? Slithy tove perhaps:) This post would perhaps make an English teacher wince but my old maths teacher would smile. Nearly 40 years ago as a twelve year old I had a maths lesson that would have even convinced Olly that maths is a language. The first lesson with Mr.Halder consisted of one question: What is mathematics? Despite haranguing us for an hour no-one was able to come up with a satisfactory answer. We were told to write 'Mathematics is a language' on the front of our exercise books.
12. ## Scientific method

Whilst certainly not a proof, the independent discovery of certain mathematical theorems by different mathematicians with different cultural, political and economic backgrounds throughout history does lends weight to the idea that mathematics is a universal language. If we were to encounter a three-fingered alien and give him the problem of summing 2+2, an answer of 11 would be further evidence of maths being a universal language.

+1
14. ## Neutral Direction Space Time

This might help. How come we can tell what motion we have with respect to the CMB? Doesn't this mean there's an absolute frame of reference? In the words of Prof.D.Scott, University of British Columbia: 'The theory of special relativity is based on the principle that there are no preferred reference frames. In other words, the whole of Einstein's theory rests on the assumption that physics works the same irrespective of what speed and direction you have. So the fact that there is a frame of reference in which there is no motion through the CMB would appear to violate special relativity! However, the crucial assumption of Einstein's theory is not that there are no special frames, but that there are no special frames where the laws of physics are different. There clearly is a frame where the CMB is at rest, and so this is, in some sense, the rest frame of the Universe. But for doing any physics experiment, any other frame is as good as this one. So the only difference is that in the CMB rest frame you measure no velocity with respect to the CMB photons, but that does not imply any fundamental difference in the laws of physics.'
15. ## Gravity and black holes....is this right ?

Correct, you'd feel always feel the same gravitational pull from your crushed down star (provided you were external to the star when you took your measurements). Imagine what it would be like to be on the stars surface as it starts to crush down. When the star has crushed to half radius we would feel four times as heavy (inverse square force Law of Gravity). Most importantly though, we would notice an eightfold increase in the difference between the pull on our head and our feet (inverse cube law of tidal acceleration). As tidal accelerations account for the curvature of space it is easy to see that as the star crushes down space becomes increasingly more curved close to the surface. Consequently, it is possible to fall into a supermassive black hole, not realize it and die of old age, whereas falling into a stellar sized black hole would lead to being torn to pieces by tidal forces. Spacetime curvature and tidal accelerations are one and the same thing only expressed in different languages.
16. ## Destination Or The Ride

Looks don't matter, 'feel' and performance do however. ie. Scopes which are solid and smooth in operation.
17. ## Yes more questions about BB

There were no free photons in the early universe. It is thought that the first free photons came into being when the universe was 380,000 yrs old. These primordial photons have not been around long enough to 'stretch' into radio waves. The CMB was predicted in the 1940's and forgotten about for twenty years. The inflationary era of the universe pre-dates free photons.
18. ## Yes more questions about BB

1) The CMB is an artifact of a universe that was about 380,000 years old. Prior to this time, the universe consisted of an "energetic soup" that would not allow the free passage of photons (ie. it was opaque). As the 'soup' expanded and cooled it reached a point whereupon the photons became free from matter and we had light. These early photons have been red-shifted by the cosmological expansion and appear predominantly as microwaves today. 2) Not much known detail about the early universe but whatever it was it looks very much like it went bang. 3)Not if the bang was big enough. 4)If the clouds are not on the edge of the observable Universe then light would pass through them.
19. ## Weight and temperature?

No, only an apparent weight loss if we assume that the soldering iron is weighed in air (or some such fluid). A thermally expanded soldering iron 'floats better'.
20. ## Weight and temperature?

As the soldering iron heats up it of course expands, therefore it will weigh less on account of Archimedes Principle. The real question now I suppose are these effects enough to offset the relativistic mass increase?
21. ## Wave-Particle Duality

No-one knows, but what you describe is certainly what appears to happen. Feynman's explanation of the double-slit experiment is great.
22. ## TeleVue 2.5 mm EP

I have a Nagler T6 2.5mm which I use occasionally and a 3.5mm T6 that I use about twenty times more often. I use them both in a TV101. The very best planetary views (especially Mars) and best double (pi Aquilae) splits are with the 2.5mm but normally the 3.5mm gives the better views. Despite it's relatively infrequent use I would never sell the 2.5mm.
23. ## H-Beta filters

Has anyone ever tried an H-beta filter on the California Nebula?
24. ## The Best Duel Fuel cooker

I've been running a coleman sportster for over 10 years on unleaded. It is terrific. I have previously used paraffin stoves which are loads of agro when compared to the coleman.
25. ## 12mm eyepiece advice appreciated

The Vixen 13mm LVW is a possibility. Around 100 quid s/h. I have the 5mm and 8mm, both are pretty decent and very comfortable to use.
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