Ephemerides

Ephemerides, it is tables or data files that provide the calculated positions of celestial objects, or bodies. It can be planets, moons, stars, satellites etc. at regular intervals over time. They can be used in astronomy, navigation and for the prediction of the sky configuration. Ephemerides are essential for predicting where objects will be in the sky at any given time because they can provide the precise tracking of planetary motion and all related parameters, such as eclipses, satellite orbits, and more. Ephemerides can have positions in different coordinate systems. For example, equatorial and ecliptic are popular. They can also contain additional information about object velocity, distance to other objects and phase angles.

Planetary ephemerides

Planetary ephemerides are mainly focused on the positions of planets, moons, and sometimes comets and asteroids within our solar system. These datasets, depending on their accuracy can be used for spacecraft navigation, astronomical research, and solar system modelling. One of the most widely used ephemeride systems produced by NASA's Jet Propulsion Laboratory (JPL) is DE421.bsp. This file has positional data for planetary bodies over a range of years.

Usually, ephemerides are stored in SPICE BSP (Binary Spacecraft and Planet Kernel) format files, which allow fast and precise computation of celestial positions over a long time range.

Stellar Ephemerides

Stellar ephemerides track star's positions. Due to a very slow star motion in comparison with the distances, the values given in these ephemerides are very precise and can be used for extrapolation of the star positions for larger time ranges.

Satellite Ephemerides

Satellite ephemerides have information about artificial satellites in the space around Earth. These ephemerides are used for satellite communication, navigation, GPS, and observation. They provide real-time updates for the satellite motion trajectories, which can change according to human or computer commands.

Debris

Space debris, or space junk is the parts of the rockers and satellites, and other hand made ojects with lost its original functionality or trajectory withing the space around the Earth. Organizations like the U.S. Space Surveillance Network (SSN) and ESA's Space Debris Office track over 27,000 pieces of debris to prevent collisions with operational satellites and the International Space Station. This is done using Two-Line Element Sets (TLEs), which provide orbital data for tracking debris. Public databases like CelesTrak and Space-Track.org offer TLEs for real-time monitoring of thousands of objects in space.

Space debris ephemerides are crucial for prediction and avoiding collision in space. These data are used to manually adjust the satellite trajectories to avoid crashes.

Lunar Ephemerides

These ephemerides track the motion of Earth's moon. Very precise lunar ephemerides are very important for understanding tides, eclipse prediction, and missions to the moon. They also account for gravitational interactions between Earth, the moon, and other bodies.

Comet and Asteroid Ephemerides

Comet and asteroid ephemerides focus on tracking the orbits of smaller bodies in the solar system, which are not classified as planets, satellites or planetoids. Given the irregular orbits of these objects, these ephemerides are crucial for predicting close encounters with Earth, potential impacts, or plotting space missions to these bodies.

BSP - Ephemerides files

BSP (Binary Spacecraft and Planet) files are ephemeride files used to store the positions, velocities, and orientations of solar system bodies like planets, moons, spacecraft, and other objects over time. These files are created primarily by NASA’s Jet Propulsion Laboratory (JPL) for use in space navigation and research, BSP files are highly accurate and efficient for storing large datasets. They can be read and processed by Python packages such as Skyfield, Spiceypy, and Astropy, which interpret the data for various astronomical calculations. These files are essential in tasks ranging from space mission planning to simulating planetary positions.

DE421.bsp

DE421.bsp: A widely-used planetary ephemeris file produced by NASA's Jet Propulsion Laboratory (JPL). It provides positions and velocities for the Sun, Moon, planets, and major planetary satellites between the years 1900 and 2050. It's often used in astronomical and space mission applications for accurate predictions.


0 ['SOLAR_SYSTEM_BARYCENTER', 'SSB', 'SOLAR SYSTEM BARYCENTER']
1 ['MERCURY_BARYCENTER', 'MERCURY BARYCENTER']
2 ['VENUS_BARYCENTER', 'VENUS BARYCENTER']
3 ['EARTH_BARYCENTER', 'EMB', 'EARTH MOON BARYCENTER', 'EARTH-MOON BARYCENTER', 'EARTH BARYCENTER']
4 ['MARS_BARYCENTER', 'MARS BARYCENTER']
5 ['JUPITER_BARYCENTER', 'JUPITER BARYCENTER']
6 ['SATURN_BARYCENTER', 'SATURN BARYCENTER']
7 ['URANUS_BARYCENTER', 'URANUS BARYCENTER']
8 ['NEPTUNE_BARYCENTER', 'NEPTUNE BARYCENTER']
9 ['PLUTO_BARYCENTER', 'PLUTO BARYCENTER']
10 ['SUN']
199 ['MERCURY']
399 ['EARTH']
299 ['VENUS']
301 ['MOON']
499 ['MARS']

DE430.bsp

DE430.bsp: Similar to DE421 but with improved precision and extended coverage. DE430 covers the time range from 1550 to 2650 and is designed for highly accurate predictions of the Moon and planetary positions, essential for deep-space missions like the Mars and lunar landings. Also contains information about some stars.

DE440.bsp

DE440.bsp: The latest in the DE series, DE440 is used for solar system dynamics, including spacecraft navigation. It covers the years 1550 to 2650 and provides improved models for the gravitational effects of asteroids and other small bodies. It is necessary to understand that the higher precision gives slower performance and requires larger space. Also contains information about some stars.

JUP310.bsp

JUP310.bsp: Focused specifically on the Jovian system, JUP310 provides high-precision data on Jupiter’s moons. It’s used for studying interactions between the moons and for planning missions to the Jupiter system.

SAT375.bsp

SAT375.bsp: This ephemeris provides precise positions for Saturn and its moons. It's designed to support studies of the Saturnian system, including Cassini mission analysis and future exploration plans.

comet.bsp

comet.bsp: This BSP file contains ephemerides for various comets within the solar system. It includes data on their positions and trajectories, which are essential for studying their behaviour predicting their future appearances and planning observation.

Printing BSP content


from skyfield.api import load
eph = load('de421.bsp') # Use your file name
for idx in eph.codes:
    print(idx, eph.names()[idx])

TLE (Two-Line Elements) Files

TLE files are files in a standardized format for encoding the orbital elements of artificial satellites. Each TLE file typically contains two lines of data for each satellite, detailing its orbital parameters such as inclination, eccentricity, and orbital period. These parameters allow for the prediction of a satellite's position in its orbit at any given time. TLEs are widely used in satellite tracking and space situational awareness due to their simplicity and the ease with which they can be generated and parsed. For Python users, the Skyfield library can work with these files.

Minor Planet & Comet Ephemeris Service

It is possible to use the Minor Planet & Comet Ephemeris Service, but they do not provide the full data with all space objects and it is necessary to request it and parse in more manual mode.

Planet Center (MPC) to generate and access positional data for minor planets, asteroids, and comets. This service allows astronomers and researchers to request ephemeris data—tables of predicted positions—based on specific parameters like observation dates, geographic locations, and object IDs. The output typically includes the object’s right ascension, declination, distance from Earth, magnitude, and more. This data is essential for tracking near-Earth objects, studying the orbital evolution of minor bodies, and preparing observational plans for amateur and professional astronomers alike. The ephemeris data can be requested in various formats (text, CSV, HTML), and users can download it for further analysis or input it into software like Python for advanced modelling using tools such as Skyfield or SpiceyPy. The MPC-Ephem service is widely used due to its comprehensive and up-to-date coverage of minor bodies in the solar system.