Archive for the 'Astronomy' Category

Mar 20 2015

Spring is here, and welcomed by an eclipse

Published by under Astronomy,Calendars

  30 Uarain, 3041       164·16·5·30       1 Ostermonth, 1571  

Today is the start of spring in the northern hemisphere, and in the United Kingdom it was greeted by a rare partial eclipse, with between 84% and 98% of the Sun obscured by the Moon at maximum eclipse. Here are some pictures that I took of the eclipse this morning.

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Sep 22 2008

Autumnal Equinox

Published by under Astronomy,Calendars Aodhrain
1 Wintering 1564

Today is the autumnal equinox (in the northern hemisphere). Now the days will be shorter than the nights for six months and, officially, autumn begins today. In the southern hemisphere, it is the first day of spring.

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May 30 2008

Prague Orloj is a bit wonky!

Published by under Astronomy,Calendars Geamhain
10 Forelithe 1564

Have just got back from a trip to Prague. One of the highlights was seeing the “Orloj”, or Astronomical Clock. This clock shows the time and the positions of the Sun and Moon in relation to the signs of the zodiac and thus accurately indicates the time of year and the length of the day. There is a good explanation of how it works in this Wikipedia article.

Anyway, we went to see it one afternoon at just around 2:30 pm (on 26th May). I had predicted how it would look, with the Sun pointer at the beginning of Gemini and the Moon pointer in Aquarius, and right enough this was how it appeared, with the exception that it was actually an hour earlier than expected as it does not appear to be adjusted for daylight savings time:

Predicted positions

Actual positions:

However, after just a few minutes, I was surprised, if not a little shocked, to see the entire inner dial (with the signs of the zodiac) move suddenly in a clockwise direction so that the pointers were now no longer in the correct positions. I took the following picture just after 3:00 pm showing the new positions:

As can be seen, the Gemini symbol is now to the right of the Sun pointer and the Moon pointer has moved into Pisces. This dial is not meant to move so suddenly and I think it is a source of disappointment to many that there is not more noticeable movement in the parts of the clock, but it is a 24-hour dial and the clock moves very slowly. Personally I couldn’t understand why it would do this and why it would just happen to occur while I was there. Then I surmised that perhaps the inner dial was slightly loose and that it would do this when it went over to the right-hand side of the main dial. If so, then it should right itself in the morning, when the inner dial moves to the left-hand side of the main dial. Right enough, when we visited it again at around 9:15 am on 28th May, it had gone back to its proper position, showing the Sun just into Gemini, but the Moon having by this time actually moved into Pisces.

So, whilst I was a little perturbed to find the clock not as perfect as I had hoped, at least it was still showing the correct positions for part of the day. I do hope that they can get this fault resolved though.

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Dec 02 2007

Analemma effects

Published by under Astronomy Samhain

One of the effects of the analemma is that the latest sunrise and the earliest sunset in most latitiudes do not occur on the shortest day. In fact, the nearer to the equator that you are located, the further apart these events occur. At my latitude of 57 degrees north, these dates are 16 Dec (15:26) and 29 Dec (08:47) respectively. However, if you at the latitude of, say, Baltimore MD, these dates are 8th Dec (17:43) and 5 Jan (08:27) respectively. This is due to the analemma being more tilted with respect to the horizon at latitudes closer to the equator.

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Nov 29 2007

Seeing the analemma

Published by under Astronomy Samhain

I have long known about the “analemma”, but now I have actually observed it. The analemma is the apparent path of the sun in the sky, as observed at the same time each day, allowing for daylight savings time. This traces out the shape of a figure of eight in the sky (see image below) due to the tilt of the Earth and the slight ellipticity of its orbit, which causes it to travel at different speeds around the sun during the year.

One effect of this is the “Equation of Time”. This is the difference between absolute solar time, determined by the position of the sun in the sky, and the local mean time, again adjusting for daylight savings when appropriate. This difference can be as much as fifteen minutes either way, e.g. in early November the sun is as much as fifteen minutes ahead of local mean time, and in February, as much as fifteen minutes behind.

Observing this effect is difficult, however, without some fixed method of measurement, e.g. the angle of a shadow compared to fixed landmarks on the ground. In my office, the sun has gotten low enough at this time of year to shine onto my desk at around lunchtime. A few weeks back, it was shining in my face at around 12:10 GMT, before moving on. Now it is nearer 12:20 before this happens, and getting later every day.

This effect can be observed in situations like the above, or using shadows, for example of trees or lamp-posts, but in those situations there must be another object to measure it against, e.g. the windows on an office block, or whatever. Then, the position of the shadow would have to be noted each day to really see the effect, but it can be fun to do this and get a greater understanding of the workings of our wonderful and interesting planet.

The Analemma on 2 Dec 2007

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Nov 13 2007

Comet Holmes

Published by under Astronomy Samhain

I had a glimpse of this the other night. It is not very bright and rather small, and looks a bit like a fuzzy star with the naked eye. A quick look through the binoculars identified it as I could see it more clearly as a fuzzy blob beside Mirfak in the constellation Perseus. So, it is not spectacular, but interesting to see nonetheless.

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Jun 21 2007

Summer is here

Published by under Astronomy Siùfainn 

Today is the longest day this year and the exact time of the solstice is 19:07 BST (18:07 UTC). Traditionally, this day marks the beginning of Summer in the Northern Hemisphere and Winter in the Southern Hemisphere. It is a very ong day where I live as sunrise was at 04:13 BST and sunset will be at 22:07 BST. Officially though, the earliest sunrise here was on 19th June and the latest sunest will be on 25th June, at approximately the same times, presumably differing by seconds rather than minutes.

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Mar 04 2007

Total Lunar Eclipse Pics

Published by under Astronomy

 13 Herthamonth 1563   15 Lenten/Naghaid 

Here are some pictures I managed to take of last night’s spectacular lunar eclipse. I thought we were going to miss much of it due to clouds but they cleared and we got a fantastic view. During totality the moon took on a lovely coppery-red colour, which was much more apparent in the photographs than to the naked eye.

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Feb 27 2007

Total Lunar Eclipse, March 3rd/4th

Published by under Astronomy

 8 Herthamonth 1563   10 Lenten/Naghaid 

There will be a total lunar eclipse, visible from almost every part of the World, on the evening of the 3rd to the 4th of March. A nice diagram with times of the various contacts can be found HERE.

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Jan 22 2007

Crescent Moon and Venus

Published by under Astronomy

 2 Solmonth 1563   3 Snow/Riùr 

Just got back from Lanzarote, and on Saturday night I got a wonderful view of the crescent moon alongside Venus.

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