Celestia Forums

A newly discovered comet has the potential to put on a dazzling celestial display late next year, when it will be so bright you may be able to see it briefly in the daytime sky.

The discovery of the object named Comet ISON was announced Monday (Sept. 24) by Russians Vitali Nevski and Artyom Novichonok, who detected it in photographs taken three days earlier using a 15.7-inch (0.4-meter) reflecting telescope of the International Scientific Optical Network (ISON), near Kislovodsk. The new comet is officially known as C/2012 S1.

When first sighted, Comet ISON was 625 million miles (1 billion kilometers) from Earth and 584 million miles (939 million km) from the sun, in the dim constellation of Cancer. It was shining at magnitude 18.8 on the reverse scale used by astronomers to measure the brightness of sky objects (the lower the number, the brighter the object). That makes the comet currently about 100,000 times fainter than the dimmest star that can be seen with the unaided eye.

http://www.space.com/17762-newfound-com ... 012s1.html

bdfd wrote:Great info Krist

I hope the Mayans and others were wrong for the "after 21 December 2012"...
The spectacle should be at the rendezvous with this comet.

It's going to be a spectacular comet next year


Would be cool to create this as an addon

I am having problems representing its orbit in Celestia. The following ssc places Ison several megaparsecs away. I have checked the numbers, and I don't see what's the problem. Can it be that it is so close to parabolic? The "period" is insane. I know parabolic orbits cannot be represented in Celestia.

Here it is. If someone detects a problem, or manages to do it right, please tell.



Guillermo

abramson wrote:I am having problems representing its orbit in Celestia. The following ssc places Ison several megaparsecs away. I have checked the numbers, and I don't see what's the problem. Can it be that it is so close to parabolic? The "period" is insane. I know parabolic orbits cannot be represented in Celestia.

Here it is. If someone detects a problem, or manages to do it right, please tell.

Code: Select all

# Comet C/2012 S1 (Ison)
# Source: http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=C%2F2012%20S1
# Guillermo Abramson (g.abramson@gmail.com)

"C2012 S1:Ison C2012 S1" "Sol"
{
   Class "comet"
   Mesh    "roughsphere.cms"
   Texture "asteroid.jpg"
   Radius               5.0      # guess
   RotationPeriod   5.0      # guess
   Albedo               0.2      # guess
   EllipticalOrbit
   {
   Epoch                     2456164.5      # 2012-Aug-25.0 TDB
#   SemiMajorAxis        -57347341492.3674
   PericenterDistance   .01250446176504045 # more natural than semimajor axis for hyperbolic orbit
   Eccentricity            1.000000000000218
   Period                    13737660012.0E+6 #13737660012632014.93110852560939     # P = (q/(e-1))^1.5 for hyperbolic orbit
   Inclination              61.81287790235313    
   AscendingNode       295.7451926842039    
   ArgOfPericenter      345.50712732    
   MeanAnomaly         359.9999999999999    
   }
}


Guillermo

Eccentricity is the problem.

Eccentricity only works from -0.99 to 0.99 not to 1.0 or more, that's the problem

kristoffer wrote:Eccentricity is the problem.
Eccentricity only works from -0.99 to 0.99 not to 1.0 or more, that's the problem

I believe that hyperbolic orbits can be represented since long time ago. Not parabolic, though, with e=1.

On the other hand, a negative eccentricity makes no sense.

Cmet McNaught, for example, performs very well:


G

abramson wrote:

kristoffer wrote:Eccentricity is the problem.
Eccentricity only works from -0.99 to 0.99 not to 1.0 or more, that's the problem

I believe that hyperbolic orbits can be represented since long time ago. Not parabolic, though, with e=1.

On the other hand, a negative eccentricity makes no sense.

G

Just not more than 0.99
I've tried that before, 1.0 doesn't work. Doesn't matter how many zero's you have behind
Celestia can't register it

kristoffer wrote:Just not more than 0.99
I've tried that before, 1.0 doesn't work. Doesn't matter how many zero's you have behind
Celestia can't register it

I beg to difer. The McNaught definiton just given has e greater than 1 and it works.

G

abramson wrote:

kristoffer wrote:Just not more than 0.99
I've tried that before, 1.0 doesn't work. Doesn't matter how many zero's you have behind
Celestia can't register it

I beg to difer. The McNaught definiton just given has e greater than 1 and it works.

G

What version of Celestia do you have? do you have the newest one?
1.6.1

kristoffer wrote:What version of Celestia do you have? do you have the newest one?
1.6.1

I build it myself. But as said, hyperbolic orbits are allowed since long time ago.

abramson,

do we need to add a special command in the config file to implement the fadding orbit ? Currently, I don't have any fadding orbit with 1.7.0, just a small ugly gap (Mac version).

Cham wrote:do we need to add a special command in the config file to implement the fadding orbit ? Currently, I don't have any fadding orbit with 1.7.0, just a small ugly gap (Mac version).

Yep. But not commands. There are a couple of parameters to adjust in render.cpp. Search for the following and adjust OrbitWindowEnd and LinearFadeFraction to please your soul:


My modifications are shown, as well as the original values from SVN.

G

Oh, my. I found this in orbit.cpp:



This gives -14465.6 for McNaught, but -1.14695*10^11 for Ison. Something must be breaking apart because of this. Unfortunately I am not very familiar with orbit.cpp...

OK. I found the culprit: the mean anomaly. JPL elements gave it as 359.9999999999999 and this makes Celestia mad. I changed it to 0.0 ant problem solved, even for the almost parabolic orbit. So, you may use this code for an ssc for comet Ison:



I had to change the epoch to the perihelion date. Otherwise I got wrong ephemerides. I have checked this ones against other high precision software and it's OK now.

In the southern Hempisphere we will see Ison at dawn before perihelion, very close to Encke (which doesn't look at all like Celestia rendition, by the way.)

abramson wrote:OK. I found the culprit: the mean anomaly. JPL elements gave it as 359.9999999999999 and this makes Celestia mad. I changed it to 0.0 ant problem solved, even for the almost parabolic orbit. So, you may use this code for an ssc for comet Ison:

Code: Select all

# Comet C/2012 S1 (Ison)
# Source: http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=C%2F2012%20S1
# Guillermo Abramson (g.abramson@gmail.com)

"C2012 S1:Ison C2012 S1" "Sol"
{
   Class "comet"
   Mesh    "roughsphere.cms"
   Texture "asteroid.jpg"
   Radius               5.0      # guess
   RotationPeriod       5.0      # guess
   Albedo               0.2      # guess
   EllipticalOrbit
   {
   Epoch               2456625.36962143133  ##2013-Nov-28.86962143
#   SemiMajorAxis       -57347341492.3674
   PericenterDistance   0.01250446176504045 # more natural than semimajor axis for hyperbolic orbit
   Eccentricity        1.000000000000218
   Period              13737660012632014.9  # P = (q/(e-1))^1.5 for hyperbolic orbit
   Inclination         61.81287790235313    
   AscendingNode       295.7451926842039    
   ArgOfPericenter     345.50712732    
   MeanAnomaly         0.000000    
   }
}


I had to change the epoch to the perihelion date. Otherwise I got wrong ephemerides. I have checked this ones against other high precision software and it's OK now.

In the southern Hempisphere we will see Ison at dawn before perihelion, very close to Encke (which doesn't look at all like Celestia rendition, by the way.)

ison.jpg

For the equation for the Period in a hyperbola, what do the letters represent?

PlutonianEmpire wrote:For the equation for the Period in a hyperbola, what do the letters represent?

q is the pericenter distance, and e is the eccentricity. See here.

abramson wrote:

PlutonianEmpire wrote:For the equation for the Period in a hyperbola, what do the letters represent?

q is the pericenter distance, and e is the eccentricity. See here.

Ah, thanks.

Maybe this old post will be helpful for the orbit definition: http://shatters.net/forum/viewtopic.php?f=4&t=2515&p=16516&hilit=hyperbolic#p16516

http://ssd.jpl.nasa.gov/horizons.cgi













http://www.aerith.net/comet/catalog/2012S1/2012S1.html

symaski62 wrote:http://ssd.jpl.nasa.gov/horizons.cgi

Code: Select all

JPL/HORIZONS                  ISON (C/2012 S1)             2012-Sep-30 02:11:37
Rec #:903902 (+COV)   Soln.date: 2012-Sep-24_12:50:02     # obs: 54 (2011-2012)
 
FK5/J2000.0 helio. eclip. TWO-BODY elements (AU, DAYS, DEG, period=Julian yrs):
 
  EPOCH=  2456164.5 != 2012-Aug-25.0000000 (CT)   Residual RMS= .32024         
    EC= 1.000000000000218  QR= .01250446176504045 TP= 2456625.369621431       
    OM= 295.7451926842039  W= 345.50712732022     IN= 61.81287790235313       
    A= -57347341492.3674   MA= 360.               ADIST= 9.999999E99           
    PER= 9.999999E99       N= 0.                  ANGMOM= .002720376           
    DAN= .01271            DDN= .78592            L= 288.7840605               
    B= -12.7431718                                TP= 2013-Nov-28.8696214     
 
Physical & non-grav parameters (KM, SEC; A1,A2,A3=AU/d^2; DT=days):
    GM= n.a.               RAD= n.a.              A1= n.a.                     
    A2= n.a.               A3= n.a.               DT= n.a.                     
    M1= 5.2                M2= n.a.               k1= 11.                     
    k2= n.a.               PHCOF= n.a.                                         
 
COMET comments
1: soln ref.= JPL#1, data arc: 2011-Dec-28 to 2012-Sep-23
2: k1=11.; TWO_BODY;

This is what occures when I using that

the comet ISON goes right into the Sun

I have made a high precision SPICE based addon for the comet. If your Celestia supports SPICE, you may prefer to use it. Besides, Celestia displays the orbit, which is nice, and it's something that (at least in my system) Celestia doesn't do for hyperbolic orbits. Download the zip file here if you like the preview! We will have a treat of double comets!

SPICE kernels are high precision orbit definitions provided by the JPL Horizons systems. They can be used by Celestia, but not all versions support SPICE. Windows versions since 1.5.0 do. If you install the addon and you don't find the comet in Celestia, your version may not support SPICE. The regular keplerian orbit (hyperbolic) definition is provided in a separate .ssc file if you wish to use it in that case.

EDIT: I noted today that Celestia 1.6.1 plots the orbit with some nasty artifacts around perihelion. The comet, though, follows the correct path around the Sun. My build from SVN, instead, displays the right orbit. I don't know the reason of this....

Enjoy!

Guillermo