en:documentation:date_time

# Date / Time setting

From the menu: Setup → Day / Time.
You also can retrieve this dialog box by a click at the icon from the left bar, or by Setup → All configuration options → Date / Time.
You can also access directly the Animation setting by a right click on the button.

The `Date/Time` setting has three tabs:

- Time
- Simulation
- Animation

For a proper display of your chart, also make sure you set the right observation position.

## Time

With this dialog box you can set the date and time for SkyChart to use. To display a reliable chart, SkyChart needs to do many calculations which require time as a parameter. The proper date and time setting is very important to display an accurate position of the planets, comets and asteroids. The date and time is also very important to display a proper chart when you are using Alt-Az coordination grid, or when you want to check the visibility of an object in the detailed information window. You might even want to display the proper motion of stars over many years.

### The checkbox Use system time

By checking this box, SkyChart will copy the system time from your computer at the moment you check this box, or every time you open a new chart and use this time to calculate the chart. A very convenient choice when you want to display a chart of the sky at the present time.

### Setting the date and time manually

You need to uncheck the Use system time checkbox when you want to display a chart for a date / time in the future or past. You can set the date and time by usage of the appropriate combo boxes. SkyChart can calculate with dates in the range from -200'000 to +200'000 years. However, by default the planet positions are only properly calculated for dates from -3000 to +3000. You can expand this range by installing a JPL ephemeris file.
Beware with the negative years: 1BC is the year 0 and 2BC is the year -1. Note that the entered time is the local time (legal time) of the defined observatory location.
You also can set JD time by using the input area and the JD calendar dialog box.

#### fixed time buttons

Tonight: Set the time to the beginning of the astronomical twilight for today.
Actual system time: At the moment you click this button, the system time will be copied and used as if you set it manually. The active chart will be recalculated with this time. From now on, every newly opened chart also will use this time.
00h: At the moment you click this button, the system time will be set to 00:00:00 of your local time. The date will be untouched. The active chart will be recalculated with this time. From now on, every newly opened chart also will use this time.
00h UT: At the moment you click this button, the system time will be set to 00:00:00 Universal Time. The date will be untouched. The active chart will be recalculated with this time. From now on, every newly opened chart also will use this time.

### The checkbox Auto Refresh

If you want SkyChart to automatically display an updated chart, you need to check this checkbox. Also, set a value in seconds for the interval after which you want SkyChart to generate a new chart. Keep in mind that generating charts can be a demanding task for your processor. Usually it only makes sense to auto refresh your charts when you are using the Alt-Az coordination grid in the chart. If you are observing occultations, asteroids or comets, it also can be usefull even if your chart isn't using Alt-Az grid.

By a click at the box More Options you get the possibility to change the difference between the Dynamic Time (DT) and the Universal Time (UT) used by the program. You need to set the correct value when you want to retrieve the accurate data regarding occultations. Click here to read more about time standards.

## Simulation

SkyChart can display the movement of the solar system objects (Sun, planets, moons, asteroids and comets) for a period of time in one single chart. The part of the orbit that those objects move during this time, can be displayed by a line and positions at a choosen interval.
You define the total period of time by setting values in the combo boxes Number of steps, every (which can be read as the step size or interval) and selecting a unit with the radio button group. If you set Number of steps to 10, set every to 7 and unit to day, you will display the movement of solar objects the next ten weeks from the set date and time.
With the radio buttons you can choose which solar system objects to display, if, and how you want to display labels for these objects.

## Animation

#### Real time options

Adjust the “Delay between frames” cursor to slow down the screen refresh during the animation. Put the cursor to the right for a two seconds delay or to the left for no delay. It is recommended to put it to the left when recording a movie.

#### Recording options

You first need to install the ffmpeg program to create the movie. For more detail see the installation section for your system.
Set “ffmpeg program path” to point where you install this program, or just the program name if it is within your search path (default on Linux).

Check “Record animation to file” to make a video movie. Otherwise no file are saved and the animation is just played in the current chart.

Change “Recording directory” to indicate where you want the resulting movie. The default value is not convenient as this is under an hidden folder.

“Recording prefix” is used to name the movies. Using the default, the first one will be skychart1.mp4, then skychart2.mp4, and so on.

Set “Recording extension” to change the default ffmpeg container. See ffmpeg documentation for more details.

Adjust the “Frames per second” you want for the final movie. Use a low value from 0.5 to 2 if you want the same effect as the real time animation. Use a value between 15 and 30 if you want a smooth movie, but use a smaller time increment in this case. This set the -r option of ffmpeg.

Set “Frames size” to the size you want for the movie. The default is to not change and use the size of the current chart. If you set another size the chart will be resized when the animation start. This not set any ffmpeg option.

“Additional ffmpeg options” let you any option you want to give to ffmpeg. The default value set a relatively high bit rate to give a good quality result for all the preset size and fps. You can use this field to change the bit rate, but also the video codec. See ffmpeg documentation for more information.

You can try this options from a command line window before to put them here. The image sequence from the last animation run is keep until a new animation is run. So you can use them to try new option or even use another software to assemble them. You will find the files in the tmp folder under the User settings directory.
The default command is “ffmpeg -r 10 -i %06d.jpg -b:v 18000k -bt 10000k skychart1.mp4”

It is recommended to use the VLC software to visualize the resulting video without boring with the codec installation.

## Date/Time settings are related to:

Chart Coordinate System. When you want to see what is visible above your horizon at a certain time and want to see time simulation in effect, the Chart Coordination System needs to be set to Azimutal Coordinate. There are several ways to achieve this. For example, from the menu bar: Chart → Chart Coordinate System → Alt-Az Coordinate

Solar System Probably you want to simulate movement of planets, asteroids or comets in whatever coordinate system. You need to set them visible, also here there are several ways. From the menu bar: Chart → Show Objects and check “Show Planets”, “Show Asteroids” and “Show Comets”. Or the fastest way, by clicking the appropriate icons from the object bar in object group B.