Return-Path: Received: from [74.125.149.76] (HELO na3sys009aog106.obsmtp.com) by media-motion.tv (CommuniGate Pro SMTP 4.2.10) with SMTP id 4716308 for AE-List@media-motion.tv; Wed, 16 May 2012 16:39:55 +0200 Received: from mail.stsci.edu ([130.167.238.10]) (using TLSv1) by na3sys009aob106.postini.com ([74.125.148.12]) with SMTP ID DSNKT7O8qO4kFzt9EcOlQbOy3B8kU2S+gdbD@postini.com; Wed, 16 May 2012 07:41:45 PDT Received: from EXCHMAIL2.stsci.edu ([169.254.2.40]) by EXCHCAS1.stsci.edu ([130.167.238.10]) with mapi id 14.02.0298.004; Wed, 16 May 2012 10:38:20 -0400 From: Frank Summers To: "AE-List@media-motion.tv" Subject: Re: [AE] Astronomical positioning in AE (script?) Thread-Topic: [AE] Astronomical positioning in AE (script?) Thread-Index: AQHNM3GI4XI0ntYgckCaVsvnYY5bdw== Date: Wed, 16 May 2012 14:38:18 +0000 Message-ID: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [130.167.166.11] Content-Type: multipart/alternative; boundary="_000_CBD9341915698summersstsciedu_" MIME-Version: 1.0 --_000_CBD9341915698summersstsciedu_ Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable Stephen, Greg Bacon passed along your message to me. I'm an astronomer in the Office= of Public Outreach at the Space Telescope Science Institute (home of Hubbl= e). Right Ascension (RA) and Declination (dec) are simply angular coordinates o= n the sky, analogous to longitude and latitude on Earth. The usual tricky p= art is that astronomers traditionally specify RA in hours-minutes-seconds a= nd dec in degrees-minutes-seconds. Your source gave you the decimal convers= ion, so everything you have should be in degrees. To get the 3D equatorial coordinates, I would write a perl script that uses= the spherical polar coordinate transform: Z =3D D * cos(90 =96 dec) X =3D D * sin(90 =96 dec) * cos(RA) Y =3D D * sin(90 =96 dec) * sin(RA) Remember that you have to convert degrees to radians (mulitply by pi/180) b= efore calling sin and cos in most programming languages. Now this gives you equatorial coordinates in which the Z axis is Earth's ro= tational axis and the XY plane is the projection of Earth's equator onto th= e sky. You may want a different coordinate system, which will require rotat= ing these coordinates. Most likely that will depend on what coordinate syst= em is being used for objects in the foreground. Other useful coordinate systems are: - ecliptic coordinates =97 XY plane is plane of Earth's orbit around the Su= n, good for solar system shots - galactic coordinates =97 XY plane is plane of Milky Way, good for extraga= lactic shots You are correct in noting that there are usually several distance measures = to a galaxy. Distance in the universe is quite difficult to measure. My adv= ice is to use only one source. It will have errors, but the errors should b= e consistent with each other. Using multiple sources can produce nonsensica= l situations (at least from an astronomers point of view). I will also note that galaxies are very small compared to the distances bet= ween them. When doing the flight from the Milky Way to the Virgo Cluster in= IMAX "Hubble 3D", the size of each galaxy was scaled up by about 4-5 in or= der to make them more visible during the flight. Don't know what you are wo= rking on, but you will likely want to do a similar scaling. Frank Summers Space Telescope Science Institute 3700 San Martin Dr Baltimore, MD 21218 410-338-4749 --_000_CBD9341915698summersstsciedu_ Content-Type: text/html; charset="Windows-1252" Content-ID: <004D7C1F73F91746B3A7712E4325D3DD@stsci.edu> Content-Transfer-Encoding: quoted-printable

Stephen,

Greg Bacon passed along your message to me. I'm an astronomer in the O= ffice of Public Outreach at the Space Telescope Science Institute (home of = Hubble).

Right Ascension (RA) and Declination (dec) are simply angular coordina= tes on the sky, analogous to longitude and latitude on Earth. The usual tri= cky part is that astronomers traditionally specify RA in hours-minutes-seco= nds and dec in degrees-minutes-seconds. Your source gave you the decimal conversion, so everything you have should= be in degrees.

To get the 3D equatorial coordinates, I would write a perl script that= uses the spherical polar coordinate transform:

Z =3D D * cos(90 =96 dec)

X =3D D * sin(90 =96 dec) * cos(RA)

Y =3D D * sin(90 =96 dec) * sin(RA)

Remember that you have to convert degrees to radians (mulitply by pi/1= 80) before calling sin and cos in most programming languages.

Now this gives you equatorial coordinates in which the Z axis is Earth= 's rotational axis and the XY plane is the projection of Earth's equator on= to the sky. You may want a different coordinate system, which will require = rotating these coordinates. Most likely that will depend on what coordinate system is being used for object= s in the foreground.

Other useful coordinate systems are:

- ecliptic coordinates =97 XY plane is plane of Earth's orbit around t= he Sun, good for solar system shots

- galactic coordinates =97 XY plane is plane of Milky Way, good for ex= tragalactic shots

You are correct in noting that there are usually several distance meas= ures to a galaxy. Distance in the universe is quite difficult to measure. M= y advice is to use only one source. It will have errors, but the errors sho= uld be consistent with each other. Using multiple sources can produce nonsensical situations (at least from a= n astronomers point of view).

I will also note that galaxies are very small compared to the distance= s between them. When doing the flight from the Milky Way to the Virgo Clust= er in IMAX "Hubble 3D", the size of each galaxy was scaled up by = about 4-5 in order to make them more visible during the flight. Don't know what you are working on, but you will likely= want to do a similar scaling.

Frank Summers

Space Telescope Science Institute

3700 San Martin Dr

Baltimore, MD 21218

410-338-4749

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