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###############################
08.3. How to plot a light curve
###############################

**RSP Aspect:** Portal

**Contact authors:** Greg Madejski and Melissa Graham

**Last verified to run:** 2025-03-04

**Targeted learning level:** intermediate

**Introduction:**
This tutorial demonstrates how to plot the light curve of a difference image analysis object (``diaObject``).
In this demonstration, an RR Lyrae star is used.
This star has coordinates RA, Dec = 62.1479031, -35.7991348 deg and an object identifier number ``diaObjectId`` = 1651589610221862935.
As is appropriate for variable stars, the forced photometry fluxes from PSF model fits in the direct (not difference) images are used.

The ``diaObjectId`` for a given coordinate can be obtained from the ``DiaObject`` table by
making a spatial query on the coordinates with a small radius (a few arcseconds) that returns the ``diaObjectId`` column.

**1. Execute the query.**
Go to the Portal's DP0.2 Catalogs tab, switch to the ADQL interface, and execute the query below.
The query will return the modified julian date (MJD) from the ``CcdVisitId`` table,
and the forced PSF flux on the direct image (``psfFlux``)
from the ``ForcedSourceOnDiaObject`` table, for the target star only.
It will also return the flux error and the band (filter) of the observation.

.. code-block:: SQL 

   SELECT cv.expMidptMJD, fsodo.psfFlux, fsodo.psfFluxErr, fsodo.band 
   FROM dp02_dc2_catalogs.ForcedSourceOnDiaObject as fsodo
   JOIN dp02_dc2_catalogs.CcdVisit as cv
   ON cv.ccdVisitId = fsodo.ccdVisitId
   WHERE fsodo.diaObjectId = 1651589610221862935


**2. The default plot is an all-filter light curve.**
The first two columns, date and flux, are plotted on the x- and y-axes of the default Active Chart for all filters (Figure 1).

.. figure:: /_static/portal-howto-lightcurves-1.png
    :name: portal-howto-lightcurves-1
    :alt: A screenshot of the default results view showing the light curve from all filters.

    Figure 1: The default results view showing the light curve with all filters as blue points.


**3. Plot a single-filter light curve.**
In the table header, in the "band" column, click on the constraint box and then select "i" in the pop-up window and click "Apply".
The plot will update to display i-band fluxes only (Figure 2).

.. figure:: /_static/portal-howto-lightcurves-2.png
    :name: portal-howto-lightcurves-2
    :alt: A screenshot of the results view with only i-band data selected.

    Figure 2: The results view with only i-band data selected and plotted.


**4. Color markers by band in a multi-band light curve.**
To set marker color based on band (filter),
create a new column in which the band is represented as a number (Figure 3)
and then a color map based on those numbers (Figure 4).
The plot will then display points colored by band (Figure 5).

.. figure:: /_static/portal-howto-lightcurves-3.png
    :name: portal-howto-lightcurves-3
    :alt: A screenshot of the "Add a column" pop-up window.

    Figure 3: The "Add a column" pop-up window to create a new column of integer numbers to represent each band.


.. figure:: /_static/portal-howto-lightcurves-4.png
    :name: portal-howto-lightcurves-4
    :width: 400
    :alt: A screenshot of the "Plot Parameters" pop-up window.

    Figure 4: The "Plot Parameters" pop-up window with the Trace Options set to define a color map based on the new "bands_ascii" column.


.. figure:: /_static/portal-howto-lightcurves-5.png
    :name: portal-howto-lightcurves-5
    :alt: A screenshot of the results view with plotted points colored by band.

    Figure 5: The results view with the new "bands_ascii" column and the plotted points colored by the Rainbow color map.


**Notice:**
In the future, the trick of creating an ascii column to represent band as an integer will not be needed.
The development of Portal functionality to plot multi-band light curves in which points are colored by filter is planned.

Return to the list of DP0.2 :ref:`DP0-2-Tutorials-Portal`.