Sky at Night Magazine

[Aratus]

From my location Mercury will start to pass in front of the Sun on Monday 9th May at 12:12pm (1112 UT) It finishes at 7:37pm (1837UT). Mercury is so far away from us that its position won't be very different wherever it is observed in the UK. Therefore the time won't differ by more than a minute or so across the UK.

Hopefully at least some of the afternoon will be clear enough to see it.
Either a sun filter across the front of the telescope or a solar prism will have to be used, or use the telescope to project an image on to white card. Looking at the transit through the telescope in the normal way will permanently damage the eyes, instantly!

For one reason or another I've never been able to observe a transit of Mercury, so I'm hoping this time I will!

[Gfamily2]

It's worth noting that Mercury is tiny, a lot smaller than Venus, so during the transit it'll only have an angular size of 13arc seconds. If you've ever looked at Uranus through your telescope you'll have some idea of the size to expect.
Projection onto card might be a challenge to see something that small.

We're going to be at Astrocamp in Brecon on the day - so we'll be hoping for sunny weather.

[Aratus]

It will be tiny - for instance there is no point in looking at the sun through 'eclipse glasses', but projection through a small refractor will show Mercury as a black dot. It will be best to project the image into a darkened area - a room or shed with thick curtains closing up the rest of the window, or even a large cardboard box! (You will probably want to do this somewhere you cannot be observed by your neighbours!) That way you can magnify the image at least 5x or more. It is certainly true that Mercury will be smaller than your average sunspot, but it is large enough to be seen via projection. It will be very black, and its relatively rapid movement across the sun will give it away.

I've done a diagram showing how Mercury might look if projected.


(btw - Mercury will be at its nearest to us in its orbit, and therefore quite a bit larger through a telescope than Uranus. It is when on the other side of the sun it looks that small.)

[Gfamily2]

.

(btw - Mercury will be at its nearest to us in its orbit, and therefore quite a bit larger through a telescope than Uranus. It is when on the other side of the sun it looks that small.)

Yes, my mistake.

[Aratus]

You were right about the actual size though. Venus in 2004 was easily visible with eclispe glasses, but this is going to need some kind of magnification. This is a projection photo I took of the Venus transit in 2004 for comparison.

Did you plan the day in Brecon, or is it just a coincidence?
I admit I've had the date in my diary for several years!

[Gfamily2]

We've been on a few Star parties and they're good fun.
This is our first time at Astrocamp - as for the dates, normally they're at the end of April, so beginning of May is unusual, but it's hard to tell which was critical:
* to avoid an inconvenient Moon
* the site would rather keep the bank holiday weekend 'open'
* the transit on the Monday

Personally, we knew that I'd be free of work commitments for the Astrocamp dates, but the transit was a coincidence. I'd probably have taken the day off anyway - as I did for Venus 2004

My favourite image from the day

Transit (2).jpg (48.3 KiB) Viewed 3068 times

[Aratus]

Very nice. I found myself lacking the right equipment in 2004. The 6" reflector I had was no good for projection, and I couldn't get hold of a decent filter. In the end I projected the image using binoculars on a white card in a cardboard box. A newly aquired digital camera was used to photograph the image. I was able to experiment with it until I got a decent photograph.

[Aratus]

Just to flag up once more the Mercury transit on Monday 9th May. Within a minute or so, Mercury starts the crossing at 12:12pm (1112 UT) and finally leaves at 7:40pm (1840UT)

I suspect I will lose the sun behind some trees before it finishes, so I won't be able to view or photograph the entire event. I think I will be happy to get a good sharp image. If Mercury comes near a sunspot, that seems like a good comparison, and worth a shot. At the moment the weather forecast is pretty good - but I've seen that change before.