Subject: Starry Night
Date: Tue, 16 Mar 99 18:03:15 -0500
From: Tom Andersen 
To: "Brian von Konsky" 
Mime-Version: 1.0
Status: RO

Brian,

The position of Stars on the screen in Starry Night Deluxe does not 
include the effects of proper motion or parallax. This was just too much 
of a burden for the slow processors without math units, as Starry Night 
Deluxe was built to run on. (of course it runs faster with newer pentiums 
and PPCs). 

We are planning a new version of Starry Night that will include the 
effects of proper motion. This will also use a much more accurate stellar 
database known as the Hipparcos/Thcho database. 

The effects of preccesion are simulated in Starry Night Deluxe, and that 
is what the movies on your web site shows. You should note that movies of 
star motion will look smoother if you plot the stars on a black sky, as 
Starry Night does antialiasing for the star images in this case. 

Thanks,

--Tom

>Date:        03/14  8:10 AM
>Received:    03/16  12:12 PM
>From:        Brian von Konsky, bvk@cs.curtin.edu.au
>To:          programmers@siennasoft.com
>CC:          bvk@cs.curtin.edu.au
>
>Dear Sienna Software:
>
>I have been a registered Starry Night Deluxe user for some time now, and I
>thoroughly love it!  I am an amateur astronomer, who usually uses it to
>plan before an observing session.
>
>This weekend I was reading about measuring the parallax of nearby stars
>over a six month period as a means of measuring the distance to those 
>stars
>as they move against a field of more distant stars.   I began to wonder if
>Starry Night would allow me to see this and experiment with taking virtual
>measurements of this effect.
>
>Note, that I'm uncertain that this is simulated, given the resolution and
>accuracy  needed to measure the small number of arc-seconds required in a
>typical parallax measurement. This would be around  1/3 arc-second in the
>case of Cygnus 61...
>
>Also, I was wondering about measuring the proper motion of stars, again as
>a virtual experiment.
>
>Should I be able to measure proper motion in Starry Night, or is the
>celestial sphere assumed fixed?
>
>I have a web page that shows some of the simulations I've done, but I'm
>having difficulty interpreting the results and was hoping you'd have a 
>look
>. See:
>
> http://www.cs.curtin.edu.au/~bvk/astronomy/snd/index.html
>
>motion1.mov appears to show some back-and-forth cyclic motion in a six
>month cycle that one would expect to see in the case of parallax of nearby
>stars.  There also appears to be a trend for all stars in the simulation 
>to
>move down and to the left.  I began to wonder  if this trend were due to
>proper motion of the stars.  This seemed unlikely, since they were all
>moving in the same general direction. Could it somehow be due to the fact
>that the stars in our spiral arm are all heading in the same general
>direction?  Seems unlikely to me.
>
>In motion2.mov I attempted to test this theory, but then found that the
>stars all seemed to be moving roughly around the celestial pole.  I think
>the motion I must be seeing, then, is not due to proper motion of the
>stars, but perhaps due to the precession of the earth.
>
>Any thoughts?
>
>Brian von Konsky
>
>-------------------------
>
>Brian von Konsky
>Perth, Western Australia
>
>



Tom Andersen
Sienna Software, Inc.
tandersen@siennasoft.com
www.siennasoft.com