Imaging & Double star Measures

[lunator]

I have not used the chronmetric method of measurment for double stars since I purchased the microguide.

A couple of weeks ago as I was re-reading the Bob Argyle book on doubles it occurred to me that I could use my S5600 camera like a CCD.

The maximum exposure is 15 seconds so if I let the stars drift I would get the true West postion and from this I could get the true North position.

From this it would be easy to measure the PA and the seperation would use the Chronmetric method calculation

15.0411 x t x cosdec / sin PA

To worok out t all I need to do was measure the ratio between the length of the star trail (x) and the length between where the continuation of the star trail crossed the North line and the start of the star trail (y).

This would give me the time difference between the 2 stars crossing the line which is t.

I thought I would start with a realtively easy pair theta 1 & 2 Tau.

The measurement of the image gave a PA of 347 and the distance of y= 0.35x so y = 5.25 seconds.

putting this into the equation gave me

15.0411 x 5.25 x cos15.869 / sin347 = 337.6" (arc seconds)

The WDS data says PA 348. Sep 336.7"

I am quite happy with these initial results. I dont know what the limtations are on this method but I am going to invesitage further.

I know a picture paints a thousand words so here is the image I took with the lines draw in to show how the calculations work.

I hope this helps.

Cheers

ian

[Kai]

WOW you lost me at Chronmetric

Just as well im a superficial observer or i might have to use the old grey stuff.

[Kaptain Klevtsov]

So this works by knowing that the stars trail at 15 degrees per hour, so that's one sixtieth of that per minute, which is easy, that's 15 arcminutes. So every 4 seconds the stars do one arcminute of trailing.

Snap the stars with no tracking to make the trails making note of the duration of the exposure. Work out the angle that the stars moved during the exposure, measure the trail length and work out the whole image scale. Good so far?

Then, because the trail is East - West, work out which way is North, then you can measure the spacing between the two stars and the angle, all from a single unguided snap.

If that's how it works, it sounds very straightforward for the brighter stuff, should be a winner.

Captain Chaos

[lunator]

CC

you have the idea.

The only reason I have used 15 seconds is that is the longest exposure that the S5600 can do.

The most important part is working out the time difference(t) between when the 2 stars would cross the North/South line. Doing this visually needs an illuminated wire but by taking an image I can add it in later and know it will be accurate.

If you want to take a few images of doubles I'd be happy to measure them, I may be able to add then to the WDS data I send in.

Cheers

Ian

[Kaptain Klevtsov]

Could be fun. Are there any candidates kind of straight up i.e. not going to be in a tree?

Captain Chaos

[lunator]

CC

I'll check into this

One worth considering is iota cancri.

It is fairly bright & wide (and high)

Cheers

ian