Displaying the Lightcurve of a Comet

Generating a lightcurve of a Comet

This page explains how to generate and interpret the lightcurve (or observation plot) for a comet using the available interface.

  1. Choose a Comet
    - Use the Comet dropdown to search for and select the comet you want to analyze.

  2. Select a Date Range (Optional)
    - Enter values in From date and To date to restrict the data to a specific time window.
    - If left empty, all available observations will be included.
    ⚠️ Note: If the entered dates fall outside the range of available observations, the plot will automatically display the full observation range instead.

  3. Choose Observation Type(s)
    - By default, both Visual observations and CCD observations are included.
    - Deselect one of the options if you only want to analyze a specific type of observation.

  4. Plot the Data
    - Click Plot to generate the lightcurve (or observation plot).
    - Each point on the chart represents a single observation.

Example:
Below is a screenshot of comet C/2025 A6 (Lemmon) with a date range applied:


Display Options for the Plot

You can customize which values are shown on the X-axis and Y-axis of the lightcurve plot.

X-Axis Options (Plot X value)

  • Observation date – Standard calendar date of the observation.
  • Time from perihelion – Relative time before or after the comet’s perihelion passage.
  • Heliocentric distance – Comet’s distance from the Sun in astronomical units (AU).

Y-Axis Options (Plot Y value)

  • Apparent magnitude – Observed brightness of the comet.
  • Coma diameter – Apparent size of the comet’s coma.
  • Coma DC – Degree of condensation of the coma.
  • Tail length – Observed length of the comet’s tail.
  • Tail PA – Tail position angle (orientation).
  • Heliocentric magnitude

Fitting Options

You can overlay various calculated curves or markers on the plot to highlight trends. Select one or more options from Fit options:

  • Brightness lightcurve (simple) – Standard lightcurve fit through magnitude observations.
  • Brightness lightcurve (scatter) – Forward scatter fit through magnitude observations.
  • Perihelion date – Vertical marker indicating the perihelion date.
  • Current epoch – Vertical marker showing the present date.
  • Heliocentric distance – Curve showing the comet distance from the Sun.
  • Geocentric distance – Curve showing the comet distance from Earth.
  • Elongation – Curve showing solar elongation (Sun–Earth–comet angle).
  • Phase angle – Curve showing the phase angle (Sun–comet–Earth angle).

Examples:

Figure 1. Observations of comet C/2025 A6 (Lemmon) plotted against observation date.

Figure 2. Coma diameter [′] of comet C/2023 A3 plotted against observation date.

Figure 3. Change of tail position angle (PA) over time for comet C/2004 Q2 (Machholz).

Figure 4. Comparison of simple vs. scatter lightcurve fits for observations of comet C/2023 A3 (Tsuchinshan–ATLAS).

Figure 5. Observations of comet C/2025 A6 (Lemmon) plotted against time from perihelion [days].

Figure 6. Observations of comet C/2025 A6 (Lemmon) plotted against heliocentric distance [AU].

Figure 7. Heliocentric magnitude of comet C/2025 A6 (Lemmon) against heliocentric distance [AU], with a simple lightcurve fit and heliocentric distance trend.