Vernal equinox today!

Hurrah!!! And everywhere in the world today daytime and night time are the same length, :cool:

Google chicken itza equinox, been smart folk around for millennium :)
 
According to the Weather Channel on my 'phone, on Monday (18th March) sunrise was at 6.19 am and sunset 6.22 pm.

So the daylight was 12 hours and 3 minutes.

Paul
 
Strictly speaking the equinox occurs the moment the sun crosses the celestial equator – the imaginary line in the sky above the Earth’s equator – from south to north. This happens either on March 19, 20 or 21 every year.

It's officially the start of spring, and about time!
 
Daylight hours are measured in two ways; astronomical sunrise and sunset (which are determined by the Earth's orbital characteristics) and civil sunrise and sunset (which take account of refraction). For the latter, sunrise occurs earlier and sunset occurs later than the astronomical sunrise and sunset, so the astronomical equinox occurs later in spring and earlier in autumn than the civil daylight hours would indicate.
 
AntarcticPilot said:
Daylight hours are measured in two ways; astronomical sunrise and sunset (which are determined by the Earth's orbital characteristics) and civil sunrise and sunset (which take account of refraction). For the latter, sunrise occurs earlier and sunset occurs later than the astronomical sunrise and sunset, so the astronomical equinox occurs later in spring and earlier in autumn than the civil daylight hours would indicate.
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Nice answer !

Lets hope spring weather finally arrives before easter - I have not been able to get the antifouling on yet!!
 
AntarcticPilot said:
Daylight hours are measured in two ways; astronomical sunrise and sunset (which are determined by the Earth's orbital characteristics) and civil sunrise and sunset (which take account of refraction). For the latter, sunrise occurs earlier and sunset occurs later than the astronomical sunrise and sunset, so the astronomical equinox occurs later in spring and earlier in autumn than the civil daylight hours would indicate.
Click to expand...
Yes, but at the equinox daytime will always be longer than nighttime because of the way it is defined. Sunset is when the sun's disc disappears and sunrise when it appears. If we redefined daytime as occurring between the time the centre of the sun appeared and disappeared at the horizon it would be closer to exactly 12 hours at the equinox, although refraction would still be a problem.
 
Obviously from this thread the weather in UK is still really only for "indoor sport" ie forum pontification.
I hope it improves soon for you all and it is a great summer. Meanwhile here in the antipodes had a light blanket on the bed for the first time since spring and sun is definitely setting earlier all signs that sailing is nearly done. Just a handful of races left for summer season. good luck olewill
 
nigelmercier said:
I find this sort of stuff fascinating, can you recommend any good books for numpties?
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Sorry don't know of any particular books. The website at http://earthsky.org/ has stuff at beginner level and some interesting stuff if you delve into their links. The search facility brings up lots of stuff. Search for 'quasars' and read the article on the 50th anniversary of their 'discovery'. A simple to understand explanation of how their discovery drove our current understanding of the universe.
 
nimbusgb said:
A simple to understand explanation of how their discovery [quasars] drove our current understanding of the universe.
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Drifting a little ...

I watch a lot of stuff about the universe on Discovery and Discovery Science, and I've read a few books. One thing in particular that puzzles me: after Hubble discovered the red shift, it was found that the further away the galaxies are, the faster they are moving; from this it was postulated that they are speeding up. Yes? But surely the further away they are, the further back in time we see their position. So rather than say they are going faster there, we should say they were going faster then.
 
Halo said:
Nice answer !

Lets hope spring weather finally arrives before easter - I have not been able to get the antifouling on yet!!
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Let's hope indeed. I bought the antifouling last month during a period of dry sunny weather (even if the temperature was below 10 C) but since then it has been colder and damp. When it was not snowing. Even yesterday, there were snow flurries. On the first day of spring!
 
nigelmercier said:
Drifting a little ...

I watch a lot of stuff about the universe on Discovery and Discovery Science, and I've read a few books. One thing in particular that puzzles me: after Hubble discovered the red shift, it was found that the further away the galaxies are, the faster they are moving; from this it was postulated that they are speeding up. Yes? But surely the further away they are, the further back in time we see their position. So rather than say they are going faster there, we should say they were going faster then.
Click to expand...

I think Lemaître put the theory of doppler shift forward prior to Hubble but quite right objects seen now were travelling 'then', and since some of them are 100 million light years away it was more than a couple of weekends ago! Look up at the sky and all you can see is historical! :)
 
A brain-boggling distance, to be sure, nimbus, but not even a scintilla of the half of it:

The new record holder is the galaxy MACS0647-JD, which is about 13.3 billion light-years away. The universe itself is only 13.7 billion years old, so this galaxy's light has been traveling toward us for almost the whole history of space and time.

http://www.space.com/18502-farthest-galaxy-discovery-hubble-photos.html
 
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