The Sun

[emmylou]

Hi there everybody.

Just a quick question....I have noticed that over the past few weeks the sunset times and sunrise times have changed dramatically, now don't get me wrong I know the days are now getting shorter but last week it was not getting dark till at least 10PM and now tonight for instance its going to be 9:15PM as for the sunrise last week it was daylight at just after 4AM and its now rising at 5AM the clocks don't go forward till Oct am I just being paranoid about things? or is there some logic explanation why such a big time difference is occuring? I live on the East coast of the UK.

Thanks in advance
Emmy.

[profloater]

while the days get shorter it is not symmetrical at the start and end of the day. After the longest day, june 21, there is a period when the sunrise and sunset both get later. This is due to lattitude on a tilted earth axis. The effect diminishes as the orbit approaches the equinox.

[loglo]

Hi there everybody.

Just a quick question....I have noticed that over the past few weeks the sunset times and sunrise times have changed dramatically, now don't get me wrong I know the days are now getting shorter but last week it was not getting dark till at least 10PM and now tonight for instance its going to be 9:15PM as for the sunrise last week it was daylight at just after 4AM and its now rising at 5AM the clocks don't go forward till Oct am I just being paranoid about things? or is there some logic explanation why such a big time difference is occuring? I live on the East coast of the UK.

Thanks in advance
Emmy.

You can see the cause of this effect easily with an analemma (http://www.analemma.com/Pages/framesPage.html), a composite picture of the position of the Sun at the same time of day throughout the year. The Earth moves faster in some parts of its orbit than at others, this causes the progression of the Sun in the sky to vary with it. Have a look around the site I linked to above, it has some good animations to make this easier to picture.

[Hornblower]

My calculations for that latitude show that the Sun should rise about 15 minutes later than a week ago and set about 17 minutes earlier. The slight asymmetry is from the equation of time as indicated by the analemma. It would take closer to a month for the rising and setting times to change by an hour each. This is consistent with what I observed when I spent five weeks in Edinburgh from late July to the end of August for the 1996 festival.

[emmylou]

Thanks guy for clearing that up for me :)

Thanks loglo for the link just having a look now.

I tend to think way to much into things sometimes and I find it best if I tackle the problem head on :)

[Hornblower]

You can see the cause of this effect easily with an analemma (http://www.analemma.com/Pages/framesPage.html), a composite picture of the position of the Sun at the same time of day throughout the year. The Earth moves faster in some parts of its orbit than at others, this causes the progression of the Sun in the sky to vary with it. Have a look around the site I linked to above, it has some good animations to make this easier to picture.

The equation of time as shown by the analemma does not address the primary effect which emmylou was concerned about. All the progression of the analemma does is skew the changes in the sunrise and sunset times a minute or so over this short interval.

Perhaps emmylou overestimated the sunrise and sunset time changes over the past week, but nevertheless they are very large compared to the equation of time effect. As the Sun's declination goes south, the azimuth of the sunrise point moves to the right rapidly, delaying the sunrise time roughly 2 minutes from one day to the next. The sunset point is moving rapidly to the left, advancing the sunset time by a similar amount. These changes are faster in the high northern latitude of the central UK than at my viewpoint in Washington, because of the shallower angle the Sun's daily path makes with the horizon. I noticed this while I was in Edinburgh.

Let me add that the variation in the summer part of the analemma would be greater if Earth's orbit was circular. The eccentricity exaggerates the effect during the winter portion around perihelion and nearly nullifies it during the summer.

[emmylou]

I am always wary about things like this, maybe I pay to much attention? thank you all for taking the time to reply, I have the horrible habit over thinking things, however with the sun ever since it rose 2 days early over iceland it has been kind of an obsession with me. I know that depending where you are in the UK it sets and rises different even by a small amount could it be I am thinking to much about it? the thing that made me post was my mums comment last night saying it was a little weird that its starting to get dark at 9:15pm and its just the end of July.

Emmy.

[Hornblower]

I am always wary about things like this, maybe I pay to much attention? thank you all for taking the time to reply, I have the horrible habit over thinking things, however with the sun ever since it rose 2 days early over iceland it has been kind of an obsession with me. I know that depending where you are in the UK it sets and rises different even by a small amount could it be I am thinking to much about it? the thing that made me post was my mums comment last night saying it was a little weird that its starting to get dark at 9:15pm and its just the end of July.

Emmy.I think that early sunrise thing in Iceland was just the popular media going overboard with an unusual but inconsequential atmospheric effect.

[Glom]

The weather can also affect how early darkness seems to set in.

[emmylou]

Hornblower yeah I kind of guessed that it was just media hype however at the time it did trigger me sucks but least I got over it :)

Glom :) yes it can its dull here tonight so we will have the lights on about 8pm so I am thinking my mind went into overdrive again.

Thank you all once again for taking the time to reply.