Ephemerides, Star Charts, Orbital Elements
The following ephemerides were generated using the JPL HORIZONS system web-interface using the following settings:
Ephemeris Type: OBSERVER
Target Body: Comet 103P/Hartley 2  or Asteroid 4 Vesta or ...
Observer Location: Geocentric 
Time Span: Start=2010-08-01, Stop=2010-09-01, Step=1 h
Table Settings: QUANTITIES=1,9,19,20,23,24,29
Users may wish to generate an ephemeris for their specific location and only for the times when the asteroid is above their local horizon and it is dark. Check out our sample ephemeris to learn how to read and interpret these files.
[These are text files. For printing, you may want to use landscape mode.]
|Hartley 2||Vesta||Ceres||Other targets?|
|field of view||charts||comments|
|27° x 17° 0 UT||20-25 Oct
28 Oct - 2 Nov
|This set of charts shows the comet's motion over several dates. The position for each date is at 0 UT. The field of view is 27° x 17°.|
|10° x 6° 0 UT||20 Oct
|This set of charts shows the comet's position at 0 UT on the given date. The field of view is 10° x 6° for each of the charts.|
|6° x 4°
17° x 11°
4° x 2°
3° x 3°
28 Oct w/ Moon
|This set of charts shows the comet's motion over a 24-hour period on the given dates. Charts are zoomed in. On 28 Oct, Hartley 2 reaches perihelion, but likely will not be visible because of the full moon passing by!|
About the Charts
Charts were generated (19 Oct) using Starry Night Pro Plus 6.2.3 with some edits in Photoshop CS3. These charts are just to help give you an approximate idea of where Hartley 2 is in the sky. To get a better fix on the position for your specific location, we suggest you generate an ephemeris for your location or use your own planetarium software setup for your location to pinpoint the target.
Table 1: Charts for finding Hartley 2 20 Oct - 11 Nov 2010.
comet 103P/Hartley 2(from Near Earth Object Program)
asteroid 4 Vesta(from Near Earth Object Program)
dwarf planet 1 Ceres(from Near Earth Object Program)
|e = 0.6951453076480744||e = 0.08862257449001465||e = 0.07913825068250649|
|i = 13.61693532515943 deg||i = 7.134063497427865 deg||i = 10.58682104881885 deg|
|q = 1.058689847276991 AU||q = 2.152593570120434 AU||q = 2.546503662734588 AU|
|w = 181.1943387446215 deg||w = 149.837350174273 deg||w = 72.58979862770518 deg|
|a = 3.472768744706854 AU||a = 2.361912320700606 AU||a = 2.765348506029223 AU|
|node = 219.7638502536721 deg||node = 103.9097233846497 deg||node = 80.39320032560637 deg|
|Q = 5.886847642136718 AU||Q = 2.571231071280779 AU||Q = 2.984193349323859 AU|
|M = 350.9753638186096 deg||M = 307.8010597409298 deg||M = 113.4104532820824 deg|
|P = 6.47 yr||P = 3.63 yr||P = 4.60 yr|
|n = 0.1522966244734063 deg/d||n = 0.2715241210144796 deg/d||n = 0.2143281753199815 deg/d|
|TP = 2010-Oct-28.25696786 (2455497.756967858577) JED||TP = 2011-Jan-31.24421044 (2455592.744210437151) JED||TP = 2009-Feb-08.85606868 (2454871.356068677083) JED|
Table 2: Table containing the orbital elements (as available from NEO site on 2010-10-18) for Hartley 2, Vesta, and Ceres for input into personal planetarium programs.
Other Targets to Observe
Although Vesta and Ceres are the targets of the Dawn mission and Hartley 2 the target of the EPOXI mission, there are other asteroids and comets related to the missions that you might want to try to observe! Scientists, engineers, and other staff associated with the missions have asteroids named after them for recognition of work done in the field. And what about Tempel 1, the orginal Deep Impact target or comet Boethin the original EPOXI target? Well, here are the links to get you started. Just use what you've learned about observing Vesta and Ceres and apply it to these.
Orbital Elements for Spacecraft
Although the Deep Impact Flyby spacecraft had a flyby of Earth on 31 Dec 2007 (as well as in 2008, 2009 and 2010), it and other spacecraft are generally too faint to actually observe.
On occasion we have provided the elements for spacecraft, but they would be for a given date. Why? When looking for the elements, I found (using the telnet option at Horizons) the elements, but it gave them to me for every day that I had specified during a timespan. So I asked...
Q: Okay, if I'm understanding the output right, the elements for the spacecraft are actually changing continuously so there's not exactly one definitive set of elements?
A: Yes, that's correct. Osculating elements can only represent the position and velocity at one instant.
The spacecraft is continuously acted on by gravity perturbations, solar radiation pressure, maneuvers, etc. Six orbital elements at some instant can't capture this time evolution.
Horizons internally uses the navigation team's trajectory model, which includes such factors. So when you obtain orbital elements over a span of time, each set is the result of accessing the underlying trajectory and converting the instantaneous state into equivalent orbital elements for that instant.
Aside from thruster events (maneuvers), the delta should be small. Suitability depends on how accurate you want the result to be.
About orbital elements
- Near Earth Object Program: graphical orbit displays of comets and asteroids, orbital elements
- Solar System Simulator: Show X as seen from Y (ie, show me Earth as seen from the DI spacecraft).
- Solar System Dynamics: various tools including Horizons ephemeris generator, orbital elements
- Minor Planet Center: various tools including ephemeris generator, orbital elements