Poor Mickey

Sometimes when you’re looking around for something to scan in your new-ish CT scanner the answer just lands in your lap.

I’ve been doing #xraymyadvent again this year, but thought I’d test out the new scanner with an item more in keeping with the scanner’s intended use. Searching around the lab I found no obvious items. Until I looked down at the floor, this is what I found.

A poor dead mouse.
This is just 60 projections from the full CT scan – it looks like the scanner worked well.

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!

Eclipse chasing

Can you really be an eclipse chaser if you’ve only actually chased one eclipse?
My chased eclipse was August 1999 – south west England. Back in the mid 1980s I had a book of fascinating astronomical facts, it listed the dates of upcoming eclipses until the far-off Year 2000. I decided that I’d see that one, and as time passed, I did find myself watching very cloudy skies from a side road near the hurlers stone circle. The sky did darken at the appointed time, the surrounding fields lit up with camera flashes and there was a genteel sense of disappointment when the sky cleared for a glorious sunny afternoon shortly after the end of the eclipse.

I’ve since caught a few other eclipses visible from London, but I’d not gone out of my way to travel to see any. I’ll not count the North American October 2014 partial eclipse as chasing because I was already in the country for other reasons.

Of course it was cloudy for the big event today. My preparation of solar film, pinholes and time-lapse camera was for nothing. With about ten minutes until first contact between sun and moon, I decided I’d at least have a try at logging the change in light levels.

I quickly bodged together an Arduino, an SD card and a light sensor, and put it in the garden. The plan being the thick cloud cover may stop be seeing the ellipse directly, but would act as a perfect diffuser for making whole-sky light level measurements.

Quick and dirty light logger

The graph shows the result – it got dark(er) when it should have.

eclipse2015

The y-axis units should be Lux, but are uncalibrated.

Other eclipses during my life.

July 1982 – No memory of this one.
December 1982 – No memory of this one either.
May 1984 – Vague memory of my Grandfather trying to view this though smoked glass.
May 1994 – Watched this though a pinhole in card held up to my eye.
October 1996 – I must have watched this, but I can’t recall it.
August 1999 – The big one, had planned to watch this since the mid 1980s. Got stuck in traffic close to our chosen viewing spot (along with half of Cornwall and the BBC), watched from the side of the road. Cloudy, but magic.
May 2003 – Far too early for me.
October 2005 – Set up with telescope and camera at work, clouds rolled in. Managed to get the occasional glimpse of the sun in projection though the telescope.
March 2006 – May have tried to watch this one, but it was only a tiny fraction partial eclipse and I was deep in PhD writing up, so no memory of this eclipse.
August 2008 – Another tiny fraction partial eclipse, I think I tried to spot it using a stack of CDs as a solar filter.
January 2011 – Early and cloudy, nothing seen.
October 2014Nicely visible from a front porch in Minneapolis
March 2015 – as above, cloudy but at least some data from the eclipse.