Release 2.4.6.0 January 21, 2023: Solar System View Improvements for Extreme Orbits
The recent appearance of the "Green Comet, C/2022 E3 or ZTF, has created a need for some improvement to the Solar System View for objects with extreme orbits.
Users have asked how to view this newly discovered object in Tidewater Planetarium. The comet is not part of the built-in planetary object set, but Tidewater Planetarium lets you add "User Defined Planets" for just such situations as this.
C/2022 E3 is an extreme comet. It is in a 50,000 year orbit that is SO eccentric, NASA's approximation as it passes through the inner solar system is actually a parabola - not an orbit at all. It's not until C/2022 E3 gets some distance from the inner planets that it will settle back into it's long, skinny orbit.
To obtain the orbital parameters for C/2022 E3, we went to NASA/JPL's Horizons web application and requested data on comet's orbit around the solar system baricenter. This gave us everything except accurate semi-major axis and eccentricity. From estimates of C/2022 E3's obital period and closest approach to the Sun, we computed those two values for a smooth Kepler orbit.
Version 2.4.6.0 was pulled forward to release a set of improvements made valuable by C/2022 E3's extreme orbit. It is MUCH larger than orbits of any other object, and it's eccentricity causes the orbit to have an extremely tight loop as it passes the Sun at high speed. These features challenged our user-interface design, and it did not present a clearly understandable view in some cases.
V2.4.6.0 adds a list of improvements to help with this and other extreme viewing conditions. They are summarized in the release notes.
The orbital data we assembled for the Green Comet are as follows:
LONGITUDE of the ASCENDING NODE: 302.7 deg (rotates the orbit around the axis of the ecliptic plane)
ARGUMENT of PERIAPSIS: 145.9 deg (rotates the orbit around its perpendicular axis)
INCLINATION: 109.1 deg (angle between the comet's orbit and the plane of the Earth's orbit. < 90 deg means it orbits in the opposite direction from the planets. "Retrograde orbit".)
SEMI_MAJOR AXIS: 1357.3 AU (Half the distance along the orbit's long axis. 1 AU is the distance from the Sun to the Earth)
ECCENTRICITY: .9991 (0 = perfect circle, 1 = parabola)
MEAN ANOMOLY: .0001 deg (Position of the comet along its orbit. This will change from day to day, Once you set it, the software always present the correct position for the simulated time.) You may have to guess at this parameter, or go to a source like NASA/JPL Horizons to get a current value.
With these six numbers you can define an orbit for a "User-Defined Planet" in the software. For display purposes, we used a very large diameter (1,000,000 km) to simulate the large gas "coma" of the comet and a very low reflectivity (.007) to simulate the fact that most sunlight is not reflected by the gas. Of course, once it gets far from the sun, the gasses will go away, but ...