# Display of NEOs

It is possible to display Near Earth Objects (NEOs) in Skychart after meticulous calculation of their positions on the sky. To do these calculations, we need our position on Earth and the time for moment of display. We can obtain the results of these calculations from the Minor Planet Center or from Horizons website from NASA JPL. After that, we can copy the data in a ASCII text file and use CatGen to compile a catalogue.
We can not use the orbital elements to do a trustworthy track display of a NEO flyby!
It is strongly advised to do a latest calculation and compilation of the catalog short before observing. The track of the NEO is likely to be different from the earlier predictions!

### Why we're not using orbital elements now

Usually Skychart is very well capable to create reliable charts with comets and asteroids based on orbital elements. Because of the usual large distances, the perturbations caused by the gravity field of the Earth or other planets are only very small influences on the track of the solar system objects. In case of a flyby situation, the gravity of the Earth is one significant perturbator extra, it has a large influence on the trajectory.

Orbital elements are mathematical data to determine conical section orbits (ellipses, parabola's) of solar system objects moving around the Sun. The orbital elements are calculated based on two bodies, the object itself and the Sun. Of course, there are the perturbations by the planets, but distances are very large, so influences are little. This is why we -under normal conditions- can use orbital elements to make reliable predictions for some time.

In case of NEOs, these normal conditions are not the case. To make predicitons about time and position, we need to do calculations based on three bodies: The object itself, the Sun and the Earth. Under the extra influence of Earths gravity, the track of the object does not follow its former conical section orbit anymore. Because orbital elements describe only conical sections, these aren't helpful in case of NEOs. If you would hold on to use orbital elements during a flyby event, you wil notice great changes of the orbital element data over short periods of time. Only after the object has moved far enough from Earth's influence you can rely on the orbital elements again.

## Download of the CatGen project-files

You can use ephemerides calculations from both the Minor Planet Center (MPC) and the NASA JPL Horizons, or you can choose one of them. Skychart is capable to display catalogues of both sources in one single chart.
For our convenience, I compiled a zip file containing:

MPC.prj | The CatGen project file for the efemerides-format of MPC
Horizons.prj | The CatGen project file for the efemerides-format of NASA JPL Horizons
mpc.txt | Raw ASCII-text file as an example, containing efemerides from MPC
horizons.txt | Raw ASCII-text file as an example, containing efemerides from Horizons
mpc.hdr | Example-catalogue header, ready for usage at 2013-02-15, generated with CatGen, based at MPC data.
horizons.hdr | Example-catalogue header, ready for usage at 2013-02-15, generated with CatGen, based at Horizons data.
mpc.info2 | Example-catalogue data, ready for usage at 2013-02-15, generated with CatGen, based at MPC data.
horizons.info2 | Example-catalogue data, ready for usage at 2013-02-15, generated with CatGen, based at Horizons data.
README.txt | Short description of the purpose of these files.

First of all, download this zip file and save it in the directory where you want to store your catalogues. With windows, the standard catalogue directory is `C:\Program Files\Ciel\cat`, with Linux that is `/usr/share/apps/ciel`. Unzip the file in your catalogue directory. After that, you will find a new directory named `ephemerides`. It will contain the above-mentioned files.

## Retrieval of Minor Planet Center data

Open the source of the MPC data by this link in a new Window.
Select the radio button `Return Ephemerides`, in case it wasn't selected. Enter the object identification(s) in the rectangular window for which you want generate the catalogue, for example 2012 DA14.
Select of enter at the same page also:

- The wished start date for the calculations, in Universal Time. Several formats are allowed, for example
  - `2013 02 15 194600` is 07:46:00 PM UT (h:m:s) at february 15th 2013
  - `2013/02/15.75` is february 15th 2013 at 6:00 PM UT.
- The number of positions that you demand to be calculated (`number of dates to output`).
- Optional: enter a number in the text box (`Ephemeris interval`) if you want to an interval for the number of time units. You will select this time unit next at Ephemeris units.
- Your wished time unit (`Ephemeris units`) in days, hours, minutes or seconds.
- In decimal notation: `(longitude)`, the `(latitude)` and the `(altitude)` above sea level in meters of the site of your observations.
- Keep selected: `full sexagesimal`, `total motion and direction`, `”/min`.
- Select according to your preference `Measure azimuths`.
- Keep selected: `Format for elements output: none`.
- Click at the `Get ephemerides/HTML page` button.

    2013 02 15 180000 11 46 49.9 -59 00 03   0.00036 0.988  105.1  74.9   9.6 1164.89    006.0    128  -54   -11   0.30   128  +45        54 078.6 / Map / Offsets
    2013 02 15 180100 11 47 05.7 -58 40 38   0.00036 0.988  105.4  74.6   9.8 1178.23    006.0    127  -54   -11   0.30   129  +45        54 078.5 / Map / Offsets
    2013 02 15 180200 11 47 21.4 -58 21 00   0.00036 0.988  105.7  74.3   9.7 1191.74    005.9    127  -54   -12   0.30   129  +45        54 078.4 / Map / Offsets
    2013 02 15 180300 11 47 36.9 -58 01 07   0.00036 0.988  105.9  74.0   9.7 1205.47    005.9    126  -53   -12   0.30   129  +45        54 078.2 / Map / Offsets
    2013 02 15 180400 11 47 52.4 -57 41 01   0.00035 0.988  106.2  73.8   9.7 1219.36    005.8    126  -53   -12   0.30   129  +45        54 078.1 / Map / Offsets
    2013 02 15 180500 11 48 07.7 -57 20 41   0.00035 0.988  106.5  73.5   9.7 1233.43    005.7    125  -53   -12   0.30   130  +44        54 078.0 / Map / Offsets
    2013 02 15 180600 11 48 22.9 -57 00 07   0.00035 0.988  106.8  73.2   9.7 1247.67    005.7    125  -53   -12   0.30   130  +44        54 077.9 / Map / Offsets
    2013 02 15 180700 11 48 38.0 -56 39 18   0.00035 0.988  107.1  72.9   9.6 1262.14    005.6    124  -52   -12   0.30   130  +44        55 077.8 / Map / Offsets

Now open in the earlier created `ephemerides` directory the file MPC.txt using an ASCII-editor (i.e. notepad of vi). Select in the browser containing the generated MPC-efemerides only those lines that contain position data. Copy the lines in the MPC.txt document and save it. We are going to use this document as an Input catalog file with CatGen.

If you don't want to use ephemerides data from Horizons you can savely skip the next paragraph and continue with Genereration of an ephemerides catalogue with CatGen.

## Retrieval of Horizons position data

Open this link in a new window.
Adapt your settings like the example below.

- Select for Ephemeris Type `Observer Tables`.
- Enter your demanded object at Target Body.
- Click under Specify Observer Location: at the line `specify latitude, longitude, and altitude` and set the coordinates and altitude above sea level at Specify Observer Coordinates. After that, click the button Use specified Coordinates.
- Next, set the time range for which you want to retrieve the position data.

Ephemeris Type | [change] | : OBSERVER
Target Body | [change] | : Asteroid (2012 DA14)
Observer Location | [change] | : user defined ( 5°52'07.0”E, 51°49'24.0” N, 60 m )
Time Span | [change] | : Start=2013-02-15 19:00, Stop=2013-02-16 02:00, Step=10 m
Table Settings | [change] | : defaults
Display/Output | [change] | : default (formatted HTML)

All demanded data are entered. So now, click the button Generate Ephemeris. In the Results you will find the positions like the example below.

     2013-Feb-15 19:00  m  12 00 04.31 -31 04 57.4   8.32 0.00025777599773  -3.0499410 127.3788 /L  52.6083
     2013-Feb-15 19:01  m  12 00 15.84 -30 26 57.6   8.30 0.00025656475249  -2.9902275 127.8449 /L  52.1423
     2013-Feb-15 19:02  m  12 00 27.35 -29 48 37.0   8.27 0.00025537764519  -2.9295700 128.3127 /L  51.6746
     2013-Feb-15 19:03  m  12 00 38.84 -29 09 55.8   8.25 0.00025421505430  -2.8679690 128.7818 /L  51.2056
     2013-Feb-15 19:04  m  12 00 50.31 -28 30 54.3   8.23 0.00025307735783  -2.8054258 129.2522 /L  50.7354

Now open in the earlier created `ephemerides` directory the file `horizons.txt` using an ASCII-editor (i.e. notepad of vi). Select in the browser containing the generated MPC-efemerides only those lines that contain position data. Copy the lines in the horizons.txt document and save it. We are going to use this document as an Input catalog file with CatGen.

## Generation of an ephemerides catalogue with CatGen

If you keep the default file name for the data and you not want to do any change to the provided example mpc.hdr or hori.hdr you can skip this section and go directly to Activate the catalogue.

For common documentation on the usage of CatGen click here.

From the menu: Setup → Catalog, then the tab Catalog in the dialog, click the CatGen button at the right hand side.

### CatGen Page 1

Click at the bottom of the new dialog the button Load project. Find the directory were you earlier unzipped the downloaded file and select the appropriate .prj file that belongs to the ephemerides source.
Replace at Catalog short name the identification for a short, recognizable catalogue name, max. 4 signs. For example, the last four signs from the object name.
Enter at Catalog full name the object identification combined with the date.
Click the button Input catalog files to set the input-catalog. Select the .txt file with the ephemerides data that belongs to the project file you using now.
Leave the output catalog type untouched to Text file catalog.
Click Next.

### CatGen Page 2

For MPC: Leave equinox to 2000, set epoch to the year of the date for which you're creating the chart.
For Horizons: Find in the results part of the Horizons page the equinox and epoch data. These are displayed above the coordinates table. It is likely that you will find data as `Initial FK5/J2000.0 heliocentric ecliptic osculating elements`, in that case, leave equinox to 2000. The epoch has been given in Julian format and as ordinary date. Take for the epoch the year part of the ordinary date.
Search in the results table which maximal magnitude we can expect from the object. Round the value up, and enter it in the magnitude field.
At Object type you can determine the displayed shape. Choose a simple, well recognizable shape.
Click Next.

### CatGen Page 3

Here, all needed settings are in place for the formats of MPC - or Horizons data. Click Next.

### CatGen Page 4

Now, set the path where you want to write the catalogue file. A logical place is the same directory where you placed the ASCII and .prj files.
Save your project settings by a click at the button Save project.
Now click the button Create catalog, after that, click Close.

### Activate the catalogue

From the menu: Setup → Catalog, then the tab Catalog in the dialog, click at the button Add in order the tell Skychart where to find your new catalog. Search for the `.hdr` file of the catalogue in the directory. After that, activate the catalogue by a click at the red dot. To confirm activation, it will turn green.

## Display

If you didn't change the other settings, the position of the asteroid will be displayed by a red lozenge. The catalogue will respond as if it is a deep sky catalogue, so you can set the magnitude of the stars independently from the asteroid.
In order to display the NEO in the same coordinate system that we retrieved from Horizons, check your settings: Setup → Chart, coordinates…, choose under Type of coordinates the radio button `Astrometric J2000 (mean equinox J2000, epoch of the date)`.