September’s talk

Stephen Tonkin lectures in Astronomy at Brockenhurst College and is a member of Wessex AS.  His talk was on ‘Binocular Astronomy’, and he has written a whole book on the subject.

As someone who has long known that beginners should always invest in a decent pair of binoculars before ever trying to buy a telescope I was still impressed by the nuggets of information in this talk.

Advantages of using binocular as opposed to mono vision:

  • Statistical summation gives binocular vision a 1.4 x advantage over monocular vision.
  • False stereopsis is the depth effect that you can get when looking at a deep sky object, even though it is so far away
  • You have a blind spot in each eye, but when you are looking at something with both eyes, you won’t necessarily end up seeing something with the same part of each eye.

Useful nuggets:

  • Your thumb joint fits nicely against eye socket, which makes it easier to hold binoculars steady
  • With large binoculars hold one side with both hands and rest the other side on your arm.
  • You can wear a cap and hold a finger from each hand over the front of the cap and that can keep binoculars steady.
  • A monopod with a trigger grip head is actually a very good stable base for heavier binoculars. He recommends Manfrotto.
  • Make a long dew cap for mounted binoculars by wrapping black material round the end of them.
  • Get binoculars where each side has independent focussing. That makes it easier to focus on astronomical objects.  Cap each side while you focus with the other.
  • For best quality in smaller binoculars go for roof prisms, which do not bend the light so much and are easier to focus. The limit in aperture is limited by the distance between our eyes, giving about 55mm.  Porro prisms fold the light path and make it possible to have much larger apertures.  Binoculars with Porro prisms will be heavier and cheap ones can lose collimation easily.

He also told us not to be fooled by sellers’ claims of certain standards, because the standards are not regulated, so if you’re told the optics are fully coated this does not tell us how many coatings the optics have.  The best optics have seven coatings on all surfaces.  You may think that all 10×50 binoculars have an objective glass 50mm in diameter but if you hold a piece of graph paper over the end of the binoculars you may be surprised and find the aperture is smaller.  Shine a torch into the binoculars at 6” distance and the light cylinder that comes through the eyepiece will also tell you how big the aperture is.  Another giveaway that any binoculars will be rubbish is if they have an orange bloom.  This is to remove the red end of the spectrum.  As red light scatters more easily and will show up defects in the focussing it is easier to put the bloom on, thereby reducing the amount of red light reaching the eye.

Mr Tonkin has a website =, where he goes into lots of details regarding binocular specifications.

Celestial line up on the 24th August

Saturn, Mars and Antares all line up on the evening of the 24th August.  The graphic below is for 20:45BST from Abingdon.

3 in a line

The day before Mars will be slightly to the West of the Saturn/Antares line and the day after it will be slightly to the East. Should be a nice photo opportunity and nice naked eye sight.

Clear skies,

The Tidore Total Solar Eclipse

Number one on the bucket list – total solar eclipse.

EclipseFullSizeRenderCredit: BBC

Whatever people say, there is a clear winner in the bucket list stakes. People may say ‘oh yeah, solar eclipse; I’ve seen one of them and it was good…’ But no, if you’ve ever seen a total one, you’d never be so blasé about it.

And beware, they are very addictive.

My first one was in June 1983 in Java, Indonesia. It seemed a bit of a long way to go and it was a rather expensive holiday. But I’m glad the umbraphiles in Liverpool AS worked on me and I gave in. At least I could say I’d seen one and I’d be satisfied….
So, 8 eclipse trips later, two failures (Hawaii 1991, Cornwall 1999) I ended up back in eastern Indonesia, Manado, North Sulawesi, and flew over to Ternate, North Maluku on 8th March, 2016. Ternate, and Tidore and famous for their spices, especially cloves, and are typical tropical volcanic bumps sticking out of the Maluku Sea. They were constantly capped by thick clouds on the summit. Ternate was on the centre line and many umbraphiles congregated at the Bela International Hotel there. There’s a rather special kind of relief when you arrive within the centre line. But, the more intrepid and energetic members of our tour group chose to venture out by boat early on eclipse day (9th March) so we could get to the south of Tidore and get about 20 seconds more of totality. We set out while it was still dark but it quickly began to get light as we clambered over other moored boats to get onto ours so we could make the quick trip across. There were taxis waiting for us to go down to the south of the island. Quite a hairy trip indeed, as they zapped past local traffic that had no lights. Lots of hooting and zipping down the middle of the road. (They do drive on the left side of the road normally.)

Tidore is a Muslim island, and eclipse day was a special calendar day for them too. They had also been preparing for our invasion for three years. We were quite nervous about seeing it as most of our mornings had been clear but we often had cloud come in later and the night before the eclipse there was a downpour. We had hoped it would stay clear long enough for us to see the eclipse but there was quite a lot of cloud to the south from where we finally stopped. If you saw my slides at the AGM you will see that it was a wonderful site. Incredibly clear water. One small island out to the east, which made for a picturesque view, and helped me to keep the eclipse in focus when I ran my camera on video during totality.

The locals had set up on the beach behind us and had collected loads of plastic chairs (?where from?) and had set up a large awning. They provided drinks and snacks, part funded by our hotel. They also organised a few dances, but really we just wanted to get on with it. They also wanted to take pictures of themselves with us, ‘selfies’ as they called them. They seemed to have a lot of smartphones for a place so isolated.

The clouds were threatening, and we just got first contact. You never really believe it will happen until you see that tiny bite out of the Sun. Then the bite gets bigger very quickly but by the time the Moon has covered about a third of the Sun nothing much really happens for ages, so it seems. Time seems to slow down. We’d been ready for ages. A sunspot became visible near the centre of the disc as our eyes dark adapted. Odd. You never realise the light levels dropping until something like that happens. The Sun was rising straight up, as we were just slightly north of the equator. Someone saw Venus above but it took me ages before i could see it. Mercury was also supposed to be visible but I was otherwise occupied.

As the crescent becomes slimmer in the final 15 minutes or so the sky takes on a metallic quality, but there were some high clouds and it didn’t seem so obvious this time. You can also get odd effects when you look at the shadows of leaves. You can get a pinhole effect which produces lots of crescent images of the eclipse. You also notice that shadows become blurry along one side and sharp on the other. In the final ten minutes the light levels dropped rapidly. At this point you usually get a sharp wind picking up, because of the temperature drop. It didn’t seem to happen much here in the tropical heat. My little compact camera was fixed to one of the plastic chairs with a gorilla pod. The tide was also going out in front of me, so I decided I would be able to jump down on the sand and not be bothered by the locals who were surrounding us and putting me on edge.

The locals were totally fascinated by this invasion of mainly tall, pale people with lots of gadgets. I still couldn’t believe how many had smartphones. Normally the final phases before third contact seem to go quite quickly but my body seemed to be on high alert and the last five minutes lasted a lot longer than usual.

You have to protect your eyes when looking at the Sun, even in those final minutes. Iwas using mysmall binoculars with astro-solar filters on them and my 15×70 binoculars were ready for viewing totality. So i was able to watch the crescent dwindle. In my first eclipse the crescent broke into three very distinct Baily’s beads before totality, but this time the light must have come across a more bland area on the Moon’s profile as the crescent just got lumpy in its final stages.

Then suddenly… I have videoed three eclipses now, so that I can just admire the view through my eyeballs and my binoculars, so I started the camera running before totality and stood in front of it to protect it. Wham, and the Sun imploded. So difficult to describe those few seconds as the light drops and this wonderful apparition appears, the Moon just seems to slot itself quickly over the Sun and trembles there. I had never got such an impression of the light falling into a hole and the Moon acting as a plug. Maybe it was because this eclipse was so high, 49 degrees up. China 2009 was much higher but there was a film of cloud. The Moon became very 3d, maybe because my dark adapted eyes were seeing some Earthshine. Our atmosphere means there is a constant sort of trembling. I jumped down onto the sand in front of the camera, and there is a special feeling I cannot describe. The eclipse lasted just over three minutes, and the whole body seemed to tingle and boil all over. You have to be there. I looked through the binoculars and there was a very impressive coronal streamer out at 5 o’clock on the disc and a bright pink and long prominence at 8 o’clock, near where the final crescent disappeared. The horizon around me seemed to stay very light, which surprised me, but the video shows that there was a lot more high cloud than I realised, so this would have kept the light levels up. There is usually a blackening and reddening effect where you can see the edges of the Moon’s shadow around us but not this time. The clouds also prevented us from seeing shadow bands, an effect of light refraction in the atmosphere in the very final seconds before second contact.

I was grabbed by a local while I looked through my binoculars and elbowed him away, as you see in the video. The video shows some of the locals photographing us, backs to the Sun! The locals are probably still afraid of eclipses. As in Java ‘83 there was lots of banging as the locals tried to scare the demon away that was trying to eat the Sun. You hear the racket on the video but I was oblivious to it at the time. Of course, all this hoohah worked, and the demon spat the Sun out. (t works every time.) Someone shouted it was finishing and within a second a bright diamond ring came up at 12 o clock. It seemed long and wide and the sky seemed to light up all over at the same time. That seemed odd to me, but then I noticed the high cloud all around it. I have overused the word ‘gawp’ in describing eclipses, but the brain just focuses all attention on visual input, and excludes everything else. The video shows me wiping my eyes. I am usually pouring my eyes out by the time the eclipse ends, but am not aware of it at the time.

So, forgive me if I get silly when I talk about my eclipse trips, but there is something about them that makes me feel real. Go get one for your bucket list and you’ll see what I mean. How about August 21 next year, central USA, or for a really good one, Gibraltar/Egypt, August 2nd 2027? That is part of the same saros as Hawaii 1991 and China 2009, which has given us two of the longest eclipses in these two centuries.