Asteroids and comets

AstroVizor includes asteroids Ceres, Pallas, Juno, Vesta, Chiron, several centaurs (asteroids between Saturn and Neptune), and trans-neptunian asteroids, as well as several bright comets of recent years. One can add more asteroids and comets from NASA ephemeris system HORIZONS. It allows to generate and download so called SPK files with ephemerides of asteroids and comets. Each SPK file can contain ephemerides for several objects of solar system.

The HORIZONS system can be accessed by connecting to "horizons.jpl.nasa.gov" via telnet port 6775. This will initiate a text-only terminal session. You will be taken through a series of prompts that will ask you questions needed to generate the desired information. To initiate such an interactive session from a UNIX/LINUX system command line, type:

telnet horizons.jpl.nasa.gov 6775

Most MacOS and Windows telnet programs have a dialog box in which the port number (6775) can be entered. If after connecting to "horizons.jpl.nasa.gov" you are prompted for a login name (not necessary for HORIZONS), it means the port 6775 request was not passed along by the software on your end. Some Windows terminal software does not fully implement the telnet protocol and does not send port numbers, even if you enter them. In case of success, you get the following screen:

Here the system expects the solar system object. You can enter the name or the identifier of an object followed by semi-colon ';'. An asteroid can be identified by its number (1 for Ceres, 4 for Vesta and so on). For the newly discovered asteroids that do not have a number yet, identifier may look like 2002 TX300.

For comets with short period, identifier looks like 1P/Halley (Halley comet). You should enter '1P;' or 'Halley;' but not both. Recently discovered comets may have identifier like P/2020 O3. Comets with long period have identifier like C/1995 O1 (Hale-Bopp comet). Here we enter the asteroid Chariklo:

The system proposes to confirm your input, so type "Enter" to execute the search. After a moment, your search results will be shown. If the only object is found, you will get the output with information about the orbit and some physical parameters, like this:

Here you should type "S" to proceed with generating an SPK file. However you can meet several object satifying your request. For example, if you input 'Halley;', the following output appears:

You can see the list of objects, first one is the asteroid Halley, the following items are the comet Halley for different Epochs, that is the year of comet approaching to the sun. Since comets have significant chaotic perturbations, the orbits are evaluated for each period independently. Press Enter for next line, or Space for next page, or use arrow keys to get to the end of the list:

Here you should enter the 8-digit number from the left column followed by semi-colon. Then you should get the screen like we have got for Chariklo, with SPK option in the last line.

You will then need to enter an email address and confirm by pressing "Enter" twice.

Enter 'B' letter to specify binary format of ephemeris. Text format is not supported by AstroVizor. Next, you will enter the desired start and end times for your SPK file:

Use the same date format that system proposes. Maximum period length is 200 years. For comets, use the dates around selected epoch. It will be possible to add other epochs or objects to the same SPK file.

Finally system asks if you want to add another object (or epoch) to the ephemeris file. If you enter 'Y', you can input next object (or 8-digit code for comet epoch) at the next system prompt. If you enter 'N', the final SPK file is generated and you can download it via ftp service within 10 minutes:

Here you see the information for downloading the file by FTP, you can copy the address after Full path: and paste it into your browser address line. Once you have download your file, rename it with the extension ".bsp" and put it into the AstroVizor folder, which is:

Android: Android/data/com.semnon.astrovfr

iOS: the iTunes sharing folder

MacOS: Library/Containers/com.semnon.AstroVios/Data/Documents (the Library folder is in your home folder, but it might be not visible by Finder unless you enable it in the Finder's Preferences).

Note that HORIZONS system generates ephemerides in SPK format only for asteroids and comets. After putting the file(s) into the folder, restart AstroVizor (get the screen with running application and swipe out, or in AstroVizor, save any chart with name Stop!!!).

You can add up to 25 asteroids and 24 comets. The free version supports only one asteroid and comet. AstroVizor supports now only SPK files with segment type 21 that is used in the SPK files produced by HORIZONS.