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what is a year?

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gruff5
419240.  Wed Oct 08, 2008 4:44 am Reply with quote

Davini994 wrote:
I reckon someone could get a dissertation out of this.

He he - I think your friend at uni possibly did! I had to resort to wiki to try & understand how the analemma shape comes about:

wiki wrote:
There are three parameters that affect the size and shape of the analemma: obliquity, eccentricity, and the angle between the apse line and the line of solstices. For an object with a perfectly circular orbit and no axial tilt, the Sun would always appear at the same point in the sky at the same time of day throughout the year and the analemma would be a dot. For an object with a circular orbit but axial tilt similar to Earth's, the analemma would be a figure of eight with northern and southern lobes equal in size. For an object with eccentricity similar to Earth's, but no axial tilt, the analemma would be a straight east-west line along the equator.

Though I'm not sure if wiki is a bit misleading here. It the orbit was circular, I would think there would be no east-west movement and so no figure of eight, but just an up-down line?

Mar has the most eccentric orbit in the solar system - other than mercury. So, the northern loop of its analemma is squeezed out & what's left is a teardrop.

Yeah, I love that pic on Mars also - seeing the base of the pathfinder lander and the little sojourner rover off by the rock really completes the sci-fi feel of it.

 
Fifi
419901.  Thu Oct 09, 2008 10:01 am Reply with quote

I think what gets me most Izz is that it doesn't look all that widely different to this planet. It's a bit incomprehensible that the picture is of Mars for me, but I like that feeling.

 
Davini994
419976.  Thu Oct 09, 2008 12:26 pm Reply with quote

It has to be to do mainly with the angle of rotation of the planet relative to the plane of the orbit around the star, does it not?

And also the latitude that you are measuring at...

 
gruff5
420241.  Fri Oct 10, 2008 6:06 am Reply with quote

Davini994 wrote:
It has to be to do mainly with the angle of rotation of the planet relative to the plane of the orbit around the star, does it not?

Otherwise known as 'obliquity' and also to do with how elliptical (ie not circular) the orbit is aka 'eccentricity'.

Davini994 wrote:
And also the latitude that you are measuring at...

That doesn't effect the shape, but the tilt of the analemma away from vertical. In which case I would have thought that vertical-looking analemma sundial in Valetta is not going to be accurate, as Malta is a long way away from the equator.

I guess such an analemma sundial is like an annual sundial (which was the way Tom Hanks was using it), as opposed to the usual daily sundials?

 
gruff5
420246.  Fri Oct 10, 2008 6:09 am Reply with quote

Fifi wrote:
I think what gets me most Izz is that it doesn't look all that widely different to this planet. It's a bit incomprehensible that the picture is of Mars for me, but I like that feeling.

I don't think NASA ever went to Mars. It was a set-up, filmed in a studio in the Nevada desert. Just look at the shadows around the Soujourner rover, they're at all different angles - just what you'd expect from studio lights.

;-)

 
npower1
420256.  Fri Oct 10, 2008 6:49 am Reply with quote

gruff5,

You are quite correct. NASA never did go to Mars. How can a government organisation go to Mars? But, the different angles of the shadows are caused by the studio lamps that they sent to Mars with the rover.

 
Dangriff679
420273.  Fri Oct 10, 2008 7:04 am Reply with quote

365 days!!!!!! duh

 
mckeonj
420384.  Fri Oct 10, 2008 11:02 am Reply with quote

What's another year?

 
smokie
420606.  Fri Oct 10, 2008 6:36 pm Reply with quote

mckeonj wrote:
What's another year?

Breaking the conditions of your parole.

 
gruff5
422315.  Tue Oct 14, 2008 9:23 am Reply with quote

A chap called Justin Quinnell has photographed half a year using a pinhole camera made from a drinks can, then scanning in the undevelped photo paper - clever!



This is taken at the Clifton Suspension Bridge in Bristol and the partial tracks are where the sun struggled to emerge from clouds. More at:-

http://www.newscientist.com/gallery/mg20026761900-solargraphs-show-half-a-year-of-sun/5

 
samivel
422413.  Tue Oct 14, 2008 10:47 am Reply with quote

Ooh, that's very good. Looks like a painting.

 
Southpaw
422904.  Wed Oct 15, 2008 9:04 am Reply with quote

A good book on the subject of time and how we interpret it is Mapping Time by EG Richards.

 
Nigelblt
427485.  Wed Oct 22, 2008 7:24 am Reply with quote

52 or 53 weeks, depending on the year.

I was doing some work this morning to calculate the ISO week number in any year because the inbuilt Excel function doesn’t do it properly.

The basic calculation is easy. You take the number of days since the start of the year, divide by 7, discard the fractions and add 1.

However, in the ISO week number year, January 1 is not necessarily the start of the year. It is defined as the first Monday (ISO weeks start on Monday) in the week containing 4 or more January days.
    If January 1 is a Monday, that is the start of the year
    If January 1 is Tuesday, Wednesday or Thursday, then the previous Monday (December 29, 30 or 31 of the previous calendar year) is the start of the year
    If January 1 falls on Friday, Saturday or Sunday, the following Monday (January 2, 3 or 4) is the start of the year.
To calculate the week number for any particular date, you first have to calculate the start dates for the previous, current and next years. Then, if your date is earlier than the start of the current year, you calculate the week number based on the start date of the previous year. If your date is later than the start date of the next year, you use that to calculate the week number. Otherwise, use the start date of the current year.

Because the year defined like this is always a full number of weeks and the calendar year has an extra 1 or 2 days, this is rectified by years in which January 1 is a Thursday (Wednesday in leap years) having 53 weeks. "2009" will start in 29 December 2008 and end on 3 January 2010.

 
mckeonj
427584.  Wed Oct 22, 2008 9:38 am Reply with quote

Bloody hell! ISO should Instantly Sod Off!
So, how many ISO fortnights are there in an ISO month of Sundays?

 
Davini994
427621.  Wed Oct 22, 2008 10:21 am Reply with quote

That's a jolly complicated way of expressing it nigelblt.

Do you write those little instruction manuals for domestic appliances for a living, by any chance?

;)

 

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