Tutorial on Creating Solar System Observations in APT

This article presents an example for creating a solar system observation in the JWST Astronomer's Proposal Tool (APT).

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Main article: JWST Astronomers Proposal Tool Overview

We walk through an example for creating new solar system observations in the JWST Astronomer's Proposal Tool (APT). This is a very basic example; the article Solar System Special Requirements describes in greater detail the options for constraining moving target observations.

To learn how to download APT and start a JWST proposal, see JWST Moving Targets in APT. Before this tutorial you may want to read Tutorial on Creating Solar System Targets in APT and after, Tutorial on Visualizing Dithers of a Solar System Observation in APT. If you have questions please contact the help desk

Getting started creating a Solar System observation

You must first create targets before proceeding to this step.

The workflow for this step is

  • Pick a target
  • Pick an instrument (MIRI, NIRCAM, NIRISS, NIRSpec)
  • Pick a science template (Imaging, IFU Spectroscopy, etc.)

Moving targets can be observed with any instrument and any observing template.

To create observations for your targets, click on the Observations folder and then New Observation Folder. An empty Observation Folder will be created, containing an empty Observation 1. Inside Observation 1 will be a blank form where you can select the target, instrument, template, etc.

The article APT Observations describes APT observations more generally and APT Observation Templates describes the available instrument templates. Below we give an example for setting up a NIRCam Imaging observation; other modes, of course, have their own unique parameters.

Example: NIRCam imaging

To create a NIRCam imaging observation, select NIRCAM from the Instrument drop-down, NIRCam Imaging from the Template drop-down, and one of the previously defined targets from the Target drop-down. After you have selected the template, a new form will appear at the bottom, where you can define the template's parameters such as the subarray, dither pattern, and filters. Notice how the estimated time in the Duration box changes as you tweak the parameters.

Figure 1. Selecting the observing template.

In the other tabs on the template form you can, for example, modify observation constraints such as timing and position angle under Special Requirements. These can differ between observing templates; more general information can be found in APT Special Requirements.

Figure 2. Special Requirements.

You can modify the observation windows under the Solar System Target Windows tab. As seen below, observations of Jupiter, its pre-defined satellites, and user-defined satellites will, by default, have 4 entries in the Solar System Target Windows tab for each of the Galilean satellites. Any time that a Galilean satellite eclipses Jupiter or its satellites will be automatically removed from the observing window. A list of default Solar System Target Windows can be found here.

Figure 3. Solar System Target Windows.

Let's add a solar phase constraint. In the Solar System Target Windows tab click Add Observing Window.
Figure 4. Adding a Solar System Target Window.

Select New Solar Phase Observing Window from the drop-down. You will get a pop-up menu as shown below. Under Object you can select from a list of any of your defined targets or solar system Standard Target, and likewise from the Observer drop-down menu.
Figure 5. Adding a Solar Phase Observing Window.

Solar System Target Windows

A full list of the available Solar System Target Windows, with descriptions, can be found here. A few notes about specific Solar System Target Windows:

  • Separation vs. Distance: The Separation observing window allows the user to define the separation between two objects in angular units, while the Distance observing window allows the user to specify that an observation should occur at a particular separation between two objects in distance units (i.e., AU). There are no specific target windows for defining a heliocentric or observer-centric distance; either can be specified using the Distance observing window and choosing the appropriate object (SUN or JWST) for Object 2.

  • Central Meridian Longitude: This observing window allows the user to specify a longitude on a rotating solar system object. This is similar to the Phase constraint available under the Special Requirements tab, except that the Central Meridian Longitude observing window only applies to a handful of standard targets: Mars, Jupiter, Saturn, Uranus, Neptune, Io, Europa, Ganymede, Callisto, Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Iapetus, Ariel, Umbriel, Titania, Oberon, Miranda, Triton, Pluto, and Charon. Specifying a Central Meridian Longitude constraint on an object not in this list will result in a warning when running the Visit Planner. Rotational constraints for other objects not in this list should be specified instead with the Phase constraint.

  • Transit vs. Occultation: A transit begins when the entire disk of the transiting body is in front of the transited body and ends when the limb of the transiting body crosses over the limb of the transited body. In other words, the transit duration covers only the time when the entire disk of the transiting body is on the disk of the transited body. An occultation begins when the limb of the transiting body first touches the limb of the transited body and ends when the two bodies are no longer in contact. The duration of an occultation is therefore always longer than the duration of a transit.

  • Eclipse: An eclipse begins when the limb of the eclipsed sphere first touches the umbra or penumbra (depending on which is specified) and ends when the limb of the eclipsed spheres touches the umbra or penumbra for the last time. In other words, the eclipse duration covers the entire time that any part of the eclipsed sphere is in the shadow.

The user should be aware that drop down menus for choosing solar system objects, available in a few of the Solar System Target Windows, will place targets defined by the user in the APT file first, followed by standard targets, satellites of standard targets, and JWST at the bottom. (There is a second instance of JWST between the standard targets and their satellites, and either can be used.)


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