Angular resolution of the dome of Planetarium of Majorca from Palma

WOW – what a clickbait title that is…

Back from having spent a few days between Christmas and New Year in Palma, Majorca. On the last day there I noticed I could just see the dome of the Planetarium of Majorca (or the telescope dome, I’m not sure which) from the hotel terrace. Seeing conditions were not great, but the small white point on the mountain top was clearly visible by reflected sunlight. It did look to be just on the edge of visibility, so now I’m back I wondered just how close to being invisible it really was.

Some Data:

  • Telescope dome position : 39.642528°N 2.950516°E (from wikipedia)
  • My viewing position : 39.555666°N 2.623219°E (from photographic GPS and google maps)
map
Positions of the dome and my viewing point

Some derived data:

  • Dome diameter : 15m (measured off google earth)
  • Distance between these points : 29.668km

Angular size :

equation

  • 5.056×10^-4 radians
  • 0.02897 degrees
  • 1′ 44.3″ arc seconds

This seems pretty small, how’s it compare to things we’d usually see?

  • Sun diameter : 31’30″Full Moon diameter : 29’20”
  • Planet Venus at closest  : 1’00”
  • Brightest star in the sky – Sirius : 0.005936″

(All values from wikipedia)

The dome appears larger than the brightest star in the sky and roughly the same size the planet Venus does. These are both perfectly visible, so why did the dome appear just visible to me? I’m guessing it’s because the dome was only reflecting a small amount of light, and I was viewing it against quite a bright background (blue sky) too. Atmospheric haze and thermal twinkles probably didn’t help.

So although I should have been able to see it pretty clearly (if it had been emitting it’s own light, against a dark background) , I was probably pretty lucky to have seen it at all given the atmospheric conditions.

Happy new year!

Lunar Eclipse September 2015

I do like a good eclipse, but not enough to be awake at 3am to photograph it. So, I set up a camera to take one picture every 30 seconds, pointed it roughly where I expected the moon to be at the time of maximum eclipse and set it recording.

Stacking the images with StarStaX produced this rather different view of the eclipse.

Luna Eclipse
Time lapse stacked images of the Lunar eclipse of September 2015

Using the same photographs I produced a video of the eclipse too. It starts dark until the moon moves into shot, then the moon fades out nicely, you can see the shadow of the Earth moving down the face of the moon, and then the moon reappearing.

Perseids meteor shower

I watched the meteor shower from the field at the Secret Nuclear Bunker where a group of us were camped doing radio stuff including bouncing signals off the ionized gas trail left by burned up meteors (meteor scatter).

I captured this time-lapse video which does include a few meteors as well as a pass by the ISS. The bright blob moving in from the left is the moon.

The circular trails are the stars moving across the sky around the pole star (not quite in frame)

De-capping ICs for fun and profit, but mostly fun.

Some time back, a friend @codfishcatfish was building a GPS disciplined oscillator for radio measurements. Part of the circuit uses a MAX232 device to interface the low voltage digital signals to a PC serial port. He found his cheap (from eBay) MAX232s got very hot and failed in use.

It was obvious the devices were fake, so I offered to tear one down to see what it really was, a cheap clone or a re-badged something else?

 

A couple of sacrificial fake ICs
A couple of sacrificial fake ICs

The standard technique to remove all the epoxy and metal to leave the bare silicon die is to use strong nitric acid. So I cut the legs off the chips, no point wasting acid dissolving those, and ground away some of the epoxy resin to speed up the dissolution.

ICs with legs and some of the epoxy package removed
ICs with legs and some of the epoxy package removed

Soaking the ICs for an hour in room temperature nitric acid had no discernible effect, so I heated up the acid. The reaction became very vigorous!

It took about 20 minutes to remove sufficient epoxy to see the silicon die – it also removed the lead-frame and bond-wires so there was no chance to test the ICs after de-capping.

 

Cruddy mess after the acid finishes its work
Cruddy mess after the acid finishes its work

 

After the acid had done its work the bare die was visible in both ICs
After the acid had done its work the bare die was visible in both ICs

The ICs were dried and the die removed by scraping away the carbonised epoxy with a scalpel. This done, the die could be examined under high magnification to see if it looked anything like a real MAX232 or I could see any other identifying features.

Bare die of fake MAX232
Bare die of fake MAX232

Comparison with a real MAX232 die proves these ICs are fake. The only identification I could find on the die is the following

Identification marks
Identification marks

So I’m non the wiser as to who actually made these, but the device does seem to show a general resemblance to the layout of a real MAX232 – they didn’t just program a micro-controller to do the job or something similar.

It was just a fun diversion and a chance to try something I’d wanted to do for a while. I might try to find some more interesting ICs to pull apart and take better images of.