Why 1st November?

[stargazerlily]

Hi Folks,

I'm slowly understanding how this polar aligning lark works. Was reading a fantastic post by Great_Bear the other day and he described how you can use a Planisphere to work out the transit times for Polaris by rotating the date dial so that 1st November aligns up to midnight (0 time). All the transit times for Polaris for any date can be read off for the entire year. I did this and checked with a software program ... and by jove ... it works. But I'm puzzled ... what is so special about this 1st November - midnight time alignment?

Pete

[kniclander]

do you mean transits the meridian? but doesn't the north star always appear in the same place in the sky, ie the NCP?

[brantuk]

I'm intrigued about the "1st Nov" question and confess I don't know the answer.

To answer the second question "doesn't the north star always appear in the same place in the sky" - the answer's "no". The north star makes a small circle in the sky because the Earth is actually wobbling a couple of degrees as it spins

(the NCP is actually the closest star to the axis of the Earth projected into space)

This is why polar alignment is so critical for imaging, and what makes guiding essential to keep the image in exactly the same place on the chip. Everything in space is just moving all the time lol

[kniclander]

I'm intrigued about the "1st Nov" question and confess I don't know the answer.

To answer the second question "doesn't the north star always appear in the same place in the sky" - the answer's "no". The north star makes a small circle in the sky because the Earth is actually wobbling a couple of degrees as it spins

er, not quite, it makes a tiny circle each night becasue it's not exactly at the NCP. the "wobble" causes its relative position to move quite a bit but over long periods of time.

[brantuk]

Ahhh - that's what I was trying to say - you catch on quick hehehe

[kniclander]

the old, "deliberate mistake" - a device I use myself frequently:)

[stargazerlily]

do you mean transits the meridian? but doesn't the north star always appear in the same place in the sky, ie the NCP?

By transit I think it means Polaris is directly below (in the '6pm' position) when you look through the Polar Scope. As the image in a Polar Scope is inverted, Polaris will be directly above the NCP (in the 12 o'clock position) ... I think

Pete