1

General Science / Re: What causes this optical illusion (trees at night)

« on: 01/03/2015 02:27:03 »

Anyone understand why this occurs?

Your eye is a point sink - opposite of a source. If you imagine straight lines connecting your eyes to any branch, you are only seeing the light illuminating the branches from that point of view, and as you are at the centre, it will appear to be circular.

Thank you. This makes perfect sense to me.

2

General Science / Re: What causes this optical illusion (trees at night)

« on: 01/03/2015 02:25:31 »

Anyone understand why this occurs?

Your eye is a point sink - opposite of a source. If you imagine straight lines connecting your eyes to any branch, you are only seeing the light illuminating the branches from that point of view, and as you are at the centre, it will appear to be circular.

The effect is more pronounced with wet and or icy trees.
It goes away when the tree starts to bud and leaf.

3

General Science / Why do trees produce a circular optical illusion when illuminated at night?

« on: 28/02/2015 04:44:15 »

I have noticed in winter when the limbs are bare there is an optical illusion that occurs when one places a tree between oneself and a street lamp.

Whenever a bare tree is backlit the limbs seem to be growing in concentric circles around the light.


A bare tree at night


With the light behind the tree. Had to block the light eith my hand so the camera would expose for the branches and not be washed out by the lamp.

Anyone understand why this occurs?

4

General Science / Re: How far does sound travel in sand?

« on: 28/08/2012 19:20:46 »

I think Herbert was referring to singing or booming sands when he wrote about drum sands.
http://www.pbs.org/wgbh/nova/earth/booming-sands.html

I don't know how well a thumper would have worked however.  The ones in the Lynch film look as if they would have pile driven themselves into the ground more than anything else.

5

Marine Science / Re: Would fake shark skin protect hulls from fouling?

« on: 18/08/2012 02:31:06 »

http://www.archiv.fraunhofer.de/archiv/pi-en-2004-2008/EN/press/pi/2006/12/ResearchNews12-2006-Topic4.html
^^^
Those guys are working on shark skin paint for aircraft.

6

Physics, Astronomy & Cosmology / Re: We want your space/astronomy pictures!

« on: 17/08/2012 14:30:33 »

A Shoemaker print (the sensitizer is composed of meteoritic iron).

7

General Science / Re: Why do LED tail lights trail to me and not to the rest of my family?

« on: 08/08/2012 23:26:17 »

I do wear glasses.
However it occurs with specific tail lights and not others. One car can have strobing lights while the one next to it will not.  It only occurs when I look away from the lights. But given how our vision works, only the very center of our field of view is in focus and one constantly scans around, the strobing can be very annoying.

8

General Science / Why do LED tail lights trail to me and not to the rest of my family?

« on: 08/08/2012 22:29:09 »

The family and I were riding home the other night and I was complaining about how LED lights strobe when I look away from them.  The rest of my family couldn't see it.

What's going on here?


^^^
What my family sees.


^^^
What I see.

It's just LED lights that strobe too.  Incandescent don't.  Some makes of cars are worse than others as well.  Cadillac's SUVs are especially bad. 

The trails are strobes as well, not streaks.  Do LEDs power on and off like fluorescent lights? 

9

Chemistry / Re: How to make Ferric Ammonium Citrate?

« on: 04/08/2012 20:56:30 »

Fresh from the print washer

Shoemaker test print-1

This is a kind of Kallitype print called a VanDyke. It is an Iron/Silver print.
The silver came from this US Silver Eagle, and the iron is from the meteorite on the right.

The meteorite is a Campo del Cielo meteorite that fell 4000-5000 years ago in Argentina.

10

Chemistry / Re: Why do my ice cubes grow spikes in the freezer?

« on: 01/08/2012 06:18:02 »

That was one of the first questions I asked when I joined TNS.

http://www.usatoday.com/tech/columnist/aprilholladay/2005-10-24-ice-spikes_x.htm
^^^
Long answer.

Short answer: your ice cubes freeze from the sides of the container towards the middle.  Since water expands when it freezes the water is pushed through the small hole left in the center of the ice on top of the cube and is extruded out as a spike.

11

Chemistry / Re: How to make Ferric Ammonium Citrate?

« on: 25/07/2012 04:35:03 »

My first (and probably only) batch of silver nitrate is almost complete.
I had access to a fume hood.  I vacuum filtered it several times and now the batch is sitting in a desiccator drying out. 
I'll make a small batch of VanDyke sensitizer and make a few test prints with it directly.

12

Physics, Astronomy & Cosmology / Re: How much water was created when the Hindenburg exploded?

« on: 16/07/2012 09:22:33 »

That image comparing the Hindenburg, a Boeing and the Titanic is extraordinary; I had absolutely no idea it was that big - is that picture accurate and to scale etc?

Yes it is.  It was huge to say the least.  804 feet in length for 100 passengers.
This site is an excellent resource on dirigibles: http://www.airships.net/

Wikipedia has this image to show its scale.



By the way my uncle served on the Macon during WWII.

13

Just Chat! / Re: Where do we stand legally on forum posts about commercial products?

« on: 15/07/2012 00:25:30 »

When Simon Singh was sued by the BCA they did not sue The Guardian, just Singh.  It would stand to reason that The Guardian was immune to liability (being they have deeper pockets than Singh and more likely to settle).

I can't find anything stating if the UK has an equivalent to our (US) amendment of the CDA act.

14

Chemistry / Re: How to make Ferric Ammonium Citrate?

« on: 14/07/2012 11:51:34 »

It is set up in the back garden and I won't approach it without my respirator. There is also a good breeze.
Although the breeze is probably the most important part of that.

The ridges on the side of the coin and the face are gone this morning.  It's going to take days.  Kind of a shame that the heat wave we just had has passed.  It is only going to be 33º today.  It was 42º the other day. That would have sped things up.

15

Chemistry / Re: How to make Ferric Ammonium Citrate?

« on: 14/07/2012 06:14:05 »

My nitric acid came in finally.
I have an ounce of silver dissolving now.  It's going to take quite a while it seems.  It's moving quite slowly.

16

Chemistry / Re: How to make Ferric Ammonium Citrate?

« on: 09/07/2012 17:13:22 »

Someone sent me this link:http://holoforum.org/oldforum/viewtopic.php?f=2&t=6561
Interesting, but I think it makes a blob of both green and brown forms of FAC.

17

Chemistry / Re: How to make Ferric Ammonium Citrate?

« on: 08/07/2012 19:12:56 »

Bother!
I sometimes find ebay sellers are less concerned about such matters.
Anyway, I'm currently washing all the Fe(OH)3.

How did it turn out?

18

Chemistry / Re: How to make Ferric Ammonium Citrate?

« on: 08/07/2012 03:42:46 »

Ebay did the trick. Thanks.

19

Chemistry / Re: How to make Ferric Ammonium Citrate?

« on: 05/07/2012 17:03:09 »

Good news, I'm a step closer to getting my NASA press pass.  I want to photograph an Atlas rocket launch and print that in meteorite.

20

Chemistry / Re: How to make Ferric Ammonium Citrate?

« on: 05/07/2012 14:47:15 »

Ran into a snag.  The company I ordered my chemicals from will only ship to a business address that is zoned for industrial use and not to a residence.  I work from home and they will only ship to me if my darkroom is physically separated from my property. Need to find a new source now.