# toml42

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1. ## Refractor vs Reflector

Hmm, i would definitely disagree about newts on the planetary front. The image through a smaller scope might be more aesthetically pleasing, as the image may be a more comfortable brightness and cleaner looking due to lack of central obstruction / less impact from seeing. But i don't see how a 4" scope could ever give the same amount of detail as a 10", given good conditions.
2. ## What next after Saturn?

jupiter + moons, particularly if there's a visible transit going on, or GRS is visible. people get quite excited to see things "in motion" like that, i find.
3. ## Refractor vs Reflector

The airy disc is the diffraction limited resolution, and decreases linearly with aperture. I think seeing limiting kicks in first most of the time though. some people might find the point like stars of a refractor easier to split, but i actually find the diffraction spokes of a reflector useful sometimes.
4. ## Refractor vs Reflector

In terms of visuals? no in terms of practicality / portability? yes
5. ## variable light speed

The many worlds interpretation solves that apparent paradox. In that interpretation you don't have to worry about whether any information was transmitted, you're just finding out what universe 'you' ended up in
6. ## Why you can't travel faster than the speed of light

There is no shame in admitting ignorance whilst seeking knowledge! You may have missed it at the end of one of my earlier posts, but momentum isn't really mass x velocity, this is just a convenient approximation for massive objects moving at everyday speeds. please fasten your seatbelts, as the only way to explain why requires a little maths: this is the real equation for momentum. in every day scenarios, where v is much, much smaller than c, the bottom of the fraction disappears, and we are left with the familiar p = mv however, if we're talking about light, traveling at c, with m=0, this equation no longer makes sense. you have 1-1 = 0 on the bottom, and 0 on the top. what is 0 divided by 0? it is undefined, there is no single correct result - this equation has broken down. this is why we use the alternative formulation for momentum when talking about light, because it does give meaningful answers: p = h / wavelength this is known as the de broglie formula, and bear in mind that it applies to everything - everything in the universe can be considered a wave with a characteristic wavelength!
7. ## Why you can't travel faster than the speed of light

If you travel at the speed of light, time stops! Which raises some interesting philosophical discourse, since a photon does not exist in its own reference frame! It measures no time at all between being created and destroyed, so in what sense can it be said to exist?
8. ## Why you can't travel faster than the speed of light

Well, that's not bad going on your part, considering that's the point where the collective knowledge of the human race breaks down! This is actually one of the things the LHC is trying to discover - the Higgs boson (the 'God' particle): you may have heard of it. If the standard models of particle physics are correct - and they have a pretty good track record so far - then the Higgs boson imbues every particle with mass. We should all be sitting in a Higgs field that gives us our mass. of course - this might be wrong.
9. ## Why you can't travel faster than the speed of light

I think he asked why it has mass, which is a whole other kettle of fish! We do have very accurate measurements of electron mass, i actually managed to do it myself up to about 3 dp in 1st year lab at university.
10. ## Why you can't travel faster than the speed of light

that'd be E^2 = m^2c^4 + p^2c^2 It is sometimes written like that, but i find it neater to write it with the brackets because it allows you to easily think in terms of components, by analogy to Pythagoras: a^2 = b^2 + c^2 you've got your rest mass term and your momentum term on the right, which you can think of as the vertical and horizontal sides of the triangle then the energy term on the left is the hypotenuse - it feels more intuitive to me to think of it like that
11. ## Why you can't travel faster than the speed of light

Regarding E=mc^2: This equation is only valid for stationary objects! The true equation is rarely seen because it doesn't so neatly fit on a t-shirt or coffee mug E^2 = (mc^2)^2 + (pc)^2 Where p is momentum. I wonder if this helps with the conceptual difficulty you were having Rabbithutch? if we now apply this to light, which has m=0: E^2 = 0 + (pc)^2 E = pc This is a well known result from quantum mechanics. If you're wondering how something with m=0 can have momentum, p can also be defined as planks constant (written as h) divided by the wavelength of the wave. this gives us the relation between the energy of a photon and its wavelength E = hc / wavelength from this we can see that increasing the wavelength decreases the energy of the photon, so red light has less energy than blue.
12. ## Why you can't travel faster than the speed of light

In response to the spacecraft traveling near light speed shining a light question: As one travels closer to the speed of light, their subjective time is dilated - clocks will run slower for you than for a stationary observer. You won't notice anything different, of course, but if you look outside the window, everything appears to be happening in fast-forward. light always travels at 299,792,458 m/s, no matter what speed the emitter is. let's round this up to 300,000,000, for convenience, and say you are traveling at 299,999,999 m/s. a stationary observer will say that the light beam moves away from you at 1 m/s, so far so good. you however, in your reference frame - experiencing time dilation - have a subjective second 300,000,000 times slower than your stationary friend: so you still measure light as traveling at 300,000,000 m/s! (This is not entirely physically accurate, as there is also length contraction to take into account, but it serves to demonstrate the general idea)
13. ## VLT timelapse

What a wonderful video! Watching it and being aware that the sky is the stationary object makes one dizzy :s The shots from within the dome were gorgeous.
14. ## variable light speed

No, the speed of light is a constant. It only appears to vary in materials because it interacts with it
15. ## variable light speed

I don't see why E=mc^2 couldn't hold in an earlier universe with a higher c. I suppose you'd have to sacrifice energy conservation instead then or something though... I don't think there's a good reason to think c has ever varied, but we have to explore every avenue.
16. ## T-ring ... M48 ... help?

Got myself a little confused with all the adapters and rings and all... I want to attach a canon 1000d to my telescope with a skywatcher coma corrector. The page says i need an M48-DSLR adapter - is this in addition to the regular t-ring or does it replace it?
17. ## bye rover

Poor Spirit Never forget <3
18. ## Cosmic distance record 'broken'

I'm pretty sure that's an x-ray image, but you're right, were it visible it would be noticeably more blue in real life
19. ## Cosmic distance record 'broken'

oh, it gets better, due to the expansion of the universe, it's actually more like 30 billion light years away!

congrats!
21. ## Wavelength connfusion - Any help welcome

http://apod.nasa.gov/apod/image/0008/solarspectrum_noao.jpg this is a spectrum of the sun - as you can see it's very messy! you couldn't tell a lot about this picture just by picking a few narrow wavebands, you really need the whole spectrum to make a good analysis
22. ## The Sun and what we see?

The short answer is sun is white, it emits light of all colours. However, it looks yellow when you look directly at it because all the bluer light is dispersed out in all directions - hence blue skies this is why it becomes redder at sunset, more light is being dispersed. The 'total' is still white light, clouds being white is evidence of this. The longer answer, as mike has mentioned is that our eyes having evolved under the sun have adapted to see it this way.
23. ## She is an Astronomer.....

I think Carolyn Porco is fantastic, i wish we saw more of her on tv. Positive female astronomer role models would do a world of good i think. Carolyn Porco flies us to Saturn | Video on TED.com She did get a little spot in Wonders of the Solar System.