Primitive telescope making tools

I've recently restarted my 4-inch reflector telescope project at the urging of an acquaintance from dance class. About 10 years ago I had already hogged out the curve, aiming for about a 100cm focal length, which I overshot a little. I managed to find my grinding log from back then, but it includes entries only for grits #120 and #220. I skipped #320, figuring that I can just put in (much) more time at #500; I also didn't want to deepen the curve yet more. Actually I'm not sure if I did or didn't use #320; the baby food jar in which the grit lives had lost its insulation-tape seal around the rim of the lid.

My grinding station is now the bathroom table in the otherwise unused flat in my back yard. Every other waist-height surface in my home is in use. (Yes, I need to get my ass in gear and create some more surfaces.) But anyway, unused is good, as it means there aren't any random household particles landing on my work.

According to ATM canon, I should have a wooden slab and brackets to hold the mirror. But faux-poor and lazy as I am, I simply plonked the glass on a sheet of newspaper, in turn on the bare laminated tabletop, and started grinding. Here is my setup:


That black thing is a quick-and-dirty pitch polisher. I simply softened some pitch and transferred it to a pickle jar cap, then pressed it on the mirror blank to establish some contact. The pink stuff is rouge, of course. I was completely surprised by how well this polisher worked - I got specular reflections after about 5 minutes of polishing with this thing!

Don't let Jacob Maroga leave Eskom

I would be sad to find out that Jacob Maroga, CEO of Eskom, has resigned as some news reports are reporting today.

IMHO Mr Maroga is the best man for the job Eskom (and its customers) can realistically hope to have. It's important here to decouple one's selfish kneejerk reaction to Eskom's application for 3 45% hikes in electricity tariffs from one's desire to have the right person leading the company.

• Mr Maroga has been an electrical engineer for 24 years, and I'd much prefer an electrical engineer who's been with Eskom for 14 years running an electricity supply company than some random accountant or politician type or artist type.
• Mr Maroga has been CEO since May 2007. This is roughly when the worst of the unplanned power failures in the Western Cape were coming to an end. We had a couple more bouts of planned power failures in early 2008, to be fair. Since then, I don't remember any Eskom-caused failures affecting me. My point here is that Thulani Gcabashe is rightly no longer CEO of Eskom. The power failures were not Mr Maroga's doing.
• 10 years ago, when new power stations should have started to have been built, Maroga was "Distribution Technology Manager". Do you see the lack of the word "Generation" there, or in fact anywhere in his career?
• Eskom's electricity is too cheap. Too cheap for them to make a profit (which they must, else capitalism demands they go out of business), not too cheap for us to afford. (Blame the municipalities here, not Eskom. Quick quiz - what's the single largest source of income for your municipality?) Getting rid of Jacob Maroga and replacing him with someone new won't change this fact: their electricity will still be too cheap.

So remind me: why do you want Jacob Maroga out?

Financial independence

The Elm tree and the Vine.

An extravagant young Vine, vainly ambitious of independency, and fond of rambling at large, despised the alliance of a stately Elm that grew near, and courted her embraces. Having risen to some small height without any kind of support, she shot forth her flimsy branches to a very uncommon and superfluous length; calling on her neighbor to take notice how little she wanted his assistance. Poor infatuated shrub, replied the Elm, how inconsistent is thy conduct! Wouldst thou be truly independent, thou shouldst carefully apply those juices to the enlargement of thy stem, which thou lavishest in vain upon unnecessary foliage. I shortly shall behold thee groveling on the ground; yet countenanced, indeed, by many of the human race, who intoxicated with vanity,
have despised economy; and who, to support for a moment their empty boast of independence, have exhausted the very source of it in frivolous expenses.

[Retrieved from http://www.archive.org/stream/aesopsfables00dodsrich/aesopsfables00dodsrich_djvu.txt with scannos fixed.]

Potatoes from my garden

What I don't manage to eat before it goes soft or gets hair or goes soggy or has worms, I put in the compost, or plant it. In July I planted all the leftover potatoes from a few bags I had accumulated. Luckily none were actually rotten (where they go soggy and smell like rotting flesh - yuck!), most were just a little too soft to seem nice to eat. So I planted them all.

The ones I planted in the back yard seem to have been a failure; whether it was for lack of sunlight, some bad juju in the soil (the pool backwash tends to spill over the area where I planted them), or higher mole activity, I don't know. But they barely got any leaves above ground.

By contrast, the ones in the front yard were almost immediately out, in the sun and growing like crazy. Even a month or so ago I started noticing little potatoes pushing up out of the soil. This can't be good for me to eat (solanine) but it was nice to see anyway. So last weekend I decided it was now three months and time to harvest the crop:


I'm so happy that there are some there that aren't totally tiny. Some that might as well have come from the shop! I'm not sure what to do with the tiny ones. Janine suggests using them in a salad. And the green ones freak me out. I should probably pare them down to nearly nothing if I want to survive eating them.

Anyone got some nice potato salad recipe that a kitchen-skills-challenged bachelor can make?

Tips for saving money

I was born into a stingy family, and am proud to continue its traditions.

• You waste an awful lot of toothpaste if you throw it away too soon. Rather cut open the tube and scrape out the last bits with a spoon. Use an old pair of scissors so you don't waste money blunting a new one!
• Take the train for your daily commute, if you can. Third class, even! (I chicken out here and use first class.) Taking my car every day would cost me about R350 each month; instead I pay R128 for a monthly train ticket. No parking woes, and I can go from Retreat to Cape Town as much as I like.

Black hole questions

Jillian's guide to black holes refers. There is the claim that hovering just above a black hole's event horizon must necessarily be painful. I believe the example used to justify this claim is specious: gravitational acceleration is stronger at a small black hole's event horizon than at a large one's. Recall that the Schwartzschild radius is directly proportional to the mass inside. If the gravitational acceleration still scales as 1/R^2, doesn't that make supermassive black holes' event horizons relatively benign?

As much as I contemplate black holes, I still don't grok this curved spacetime business. And especially not the spacetime around a rotating object - I just don't get this "frame dragging" business. Sure, I can look at the pretty spacetime diagrams and marvel at the light cones, but I'm in need of a Zen-like GR enlightenment.

So what exactly happens when you put your hand past the event horizon of a supermassive black hole (so you don't get squished in the process of hovering)? I imagine that spacetime is still flat enough that you won't feel any tidal forces, but then what happens to your hand? Does it tear off neatly as you put it in, blood spurting as you pull it out? Two conflicting "certainties" present themselves:

• Yes, a "detachment front" passes through your hand, likely to be quite painful. Check how much of your arm is left and you know where exactly the event horizon is.
• No, nothing happens to your hand, as far as you can tell. There's nothing special about the even horizon, they say, no signal that you've passed it.

I don't buy the rope-lowering explanation. What does it mean to "quickly" lower the rope? How many meters must we pay out? We might never see the tip pass the event horizon due to its red-shifting, but if we send Jack down the beanstalk, will he eventually reach the event horizon before climbing down an infinite length of the rope?

What happens when a system of non-black holes adopts a configuration where its whole extent fits within the Schwartzschild radius of a mass equal to the sum of the constituent masses? Imagine three borderline strangelet stars converging on a single spacetime event: Darth Vader wants them there. What happens just before they touch? We can draw a sphere around the three strangelet stars that is smaller than a Schwartzschild black hole of the same mass as the three put together. Does that mean that the 3-star system forms a black hole, even before they touch?

Update: Found a partial answer in the sci.physics FAQ.

And more puzzling still, how exactly do black holes merge? Do their event horizons bulge out toward each other or away? My reasoning for the latter is that you have two of these things fighting for the light cones between them. So how exactly do they ever manage to merge?

Oh and by the way, what is the "distance" to the center of a black hole? If I want to calculate the gravitational acceleration at a point outside its event horizon, I need to know how far I am. How do I determine that distance? A tape measure won't do, but will a triangulation give me the answer?

If anyone can explain to me what exactly a tensor is, I'd be most grateful. I once got quite far working through the problems in Schaum's Outline Series' _Tensor Analysis_, but never really "got" what those things were. To me they were just a bunch of symbols with superscripts and subscripts, which one manipulated in a particular way.

Poverty challenge

My colleagues were lamenting how pitiful the South African state pension is - the figure of R283 per month came up. (Sorry, I have no reference.) I claimed that it is possible to survive on that amount, if one reduces ones living standards sufficiently. So the discussion quickly turned into a challenge - whether I could survive on R283 for one month.

(AFAIK the state pension is almost 4 times this amount. I don't know where the figure of R283 fits in - some arbitrary definition of "below the bread line" perhaps?)

I simply do not believe that it is necessary to starve to death in this country. We have enough fat in our system that just about anybody within a couple of sigmas of the mean should be able to eke out a living, however meager.

Of course R283 doesn't go very far. I've accepted that there is no room for a private medical plan. Then again, if you ignore the quacks that advocate garlic for the treatment of AIDS, our public health system is still ticking over, if strained. As for accommodation - let's just pretend that there are an infinite number of bridges. Our weather is mild enough here in the Cape that one needn't die of exposure. But I'll stick to my own home for the Challenge Lite. And since I'm simulating unemployment, I don't really need daily transport, but if I do it'll have to be (make-believe) third-class train tickets.

I don't know if anybody wants to join me in taking on this challenge. I'm not even sure I want to go through with it myself! But I think it would be interesting to test the limits of financial stress. So I'm looking for tips on how to stretch every penny. So far I'm a little stumped on how to get enough protein; carbohydrates seem affordable enough. And let's not forget vitamins.