The Blue Sky thread.

[sixspeed]

Have to say I've never really paid much attention to the effects of what has been discussed here. I have marvelled at the brilliant blue skies we've had though over the last week however, and this morning looking out of the window, the number of vapour trails and "man-induced cloud" is incredibly apparent.

[Getragdogleg]

Yep, Its really obvious to me now just how much "cloud" the aircraft leave.

We had a few flights go over late last night and this morning when I looked out it was business almost as normal plane/sky wise, plenty of traffic again.

[Digga]

One fact not yet mentioned is prevailing wind direction.

Aside from the direct outdoors weather knowledge provided by twice daily dog walks up on the hills and the odd bit of mountain biking, my office is next to some cooling towers. So I'm pretty 'aware' of the direction stuff's blowing from. See:



Prevailing UK weather is from the southern Atlantic - south-westerly winds - but of late the wind has mostly been from the north, hence how st (actually, make that more st - we suffered their banking nonsense too) from Iceland gets here.

Edited by Digga on Wednesday 21st April 14:20

[don4l]

NoelWatson said:

don4l said:

Here in Camberley, the limiting magnitude (the dimmest stars that are visible) has been 4.7 instead of the usual 4. That is quite a significant difference.


Don
--

How do you measure that? Reference stars?

In autumn, I count the stars in the square of Pegasus, and identify them in a sky charts program, which will give their magnitude.

Otherwise, just pick an area and see which are the dimmest that you can make out. Carefully compare with the star chart with the area of sky that you are observing. As you get to the dimmest stars, you won't e quite sure if you are looking at a star or not, so confirming with the star chart is very important.

It is easier with two people. One can be sat at the laptop looking at the star chart. The other is left free to observe without losing his night vison when making the comparisons.

The first time that I did it, I was surprised at how accurate the method is. Mind you, it also depends on your eyesight. The guy who showed me the method could only see down to a quarter of a magnitude more than I could. So I suppose that my results should be preceeded with "at least".


Don
--

[DangerousMike]

is the magnitude scale linear or logarithmic?

[don4l]

DangerousMike said:

is the magnitude scale linear or logarithmic?

It definitely isn't linear.

If I remember correctly, each order of magnitude is about 5 times dimmer than the previous one. So a Magnitude 2 Star is 5 times less luminious than a magnitude 1 star.


I *might* correct this tommorow!

Don
--

[don4l]

Ah well... here is the correction.

Each magnitude is 2.5 times dimmer. So a mag 2 star is 2.5 times dimmer than a mag 1 star. A mag 3 star is 6.25 times dimmer than a mag 1.

Don
--

[NoelWatson]

don4l said:

NoelWatson said:

don4l said:

Here in Camberley, the limiting magnitude (the dimmest stars that are visible) has been 4.7 instead of the usual 4. That is quite a significant difference.


Don
--

How do you measure that? Reference stars?

In autumn, I count the stars in the square of Pegasus, and identify them in a sky charts program, which will give their magnitude.

Otherwise, just pick an area and see which are the dimmest that you can make out. Carefully compare with the star chart with the area of sky that you are observing. As you get to the dimmest stars, you won't e quite sure if you are looking at a star or not, so confirming with the star chart is very important.

It is easier with two people. One can be sat at the laptop looking at the star chart. The other is left free to observe without losing his night vison when making the comparisons.

The first time that I did it, I was surprised at how accurate the method is. Mind you, it also depends on your eyesight. The guy who showed me the method could only see down to a quarter of a magnitude more than I could. So I suppose that my results should be preceeded with "at least".


Don
--

I was thinking that you were somewhere op North where there is less light pollution. Have you been to Galloway Forest Park?

[don4l]

NoelWatson said:

don4l said:

NoelWatson said:

don4l said:

Here in Camberley, the limiting magnitude (the dimmest stars that are visible) has been 4.7 instead of the usual 4. That is quite a significant difference.


Don
--

How do you measure that? Reference stars?

In autumn, I count the stars in the square of Pegasus, and identify them in a sky charts program, which will give their magnitude.

Otherwise, just pick an area and see which are the dimmest that you can make out. Carefully compare with the star chart with the area of sky that you are observing. As you get to the dimmest stars, you won't e quite sure if you are looking at a star or not, so confirming with the star chart is very important.

It is easier with two people. One can be sat at the laptop looking at the star chart. The other is left free to observe without losing his night vison when making the comparisons.

The first time that I did it, I was surprised at how accurate the method is. Mind you, it also depends on your eyesight. The guy who showed me the method could only see down to a quarter of a magnitude more than I could. So I suppose that my results should be preceeded with "at least".


Don
--

I was thinking that you were somewhere op North where there is less light pollution. Have you been to Galloway Forest Park?

No, I haven't. I'm is Surrey, and the light pollution is awful.

Don
--

[DangerousMike]

don4l said:

Ah well... here is the correction.

Each magnitude is 2.5 times dimmer. So a mag 2 star is 2.5 times dimmer than a mag 1 star. A mag 3 star is 6.25 times dimmer than a mag 1.

Don
--

thanks

so the difference in magnitude you saw was pretty dramatic then!

[don4l]

DangerousMike said:

don4l said:

Ah well... here is the correction.

Each magnitude is 2.5 times dimmer. So a mag 2 star is 2.5 times dimmer than a mag 1 star. A mag 3 star is 6.25 times dimmer than a mag 1.

Don
--

thanks

so the difference in magnitude you saw was pretty dramatic then!

Absolutely! Even the Mrs was impressed, and she has no interest in the night sky. In fact, it was she who called me out to see it.

I cannot be sure that it was down to the absence of aircraft, but it started the night that they were grounded, and ended the night that they returned.

Don
--

[Hedders]

The end of the clear skies in the morning here, by the look of it

[Puggit]

They've gone since the day flights were allowed over UK airspace, here in Reading.

The difference is so obvious, it is saddening (and I love to fly!)

[Getragdogleg]

The picture above is exactly what I was talking about.

It was quite nice to see what the sky is supposed to look like on nice days instead of the spread out lingering trail fest we get the rest of the time.

I love flying, I love leaving this country and going somewhere else but now we have had those few days of no flying it has shown me just how much vapour and other stuff we put up there.

[supersingle]

Yep, very obvious difference here in the midlands since the planes returned.

It's astonishing. The high cloud doesn't look like contrails but it's now obvious that that is how it occurs. I'd just never twigged before.