A time-series plot showing the brightness of an astronomical object over time, designed to reveal exoplanet transit events as characteristic dips in flux. The plot displays photometric measurements with error bars against time or orbital phase, with an optional fitted transit model overlay. This visualization is fundamental in observational astronomy for detecting and characterizing planetary transits, variable stars, and other periodic brightness variations.
""" anyplot.ai
lightcurve-transit: Astronomical Light Curve
Library: plotly 6.8.0 | Python 3.13.14
Quality: 90/100 | Updated: 2026-06-20
"""
import os
import numpy as np
import plotly.graph_objects as go
# Theme tokens (Imprint palette — see prompts/default-style-guide.md)
THEME = os.getenv("ANYPLOT_THEME", "light")
PAGE_BG = "#FAF8F1" if THEME == "light" else "#1A1A17"
ELEVATED_BG = "#FFFDF6" if THEME == "light" else "#242420"
INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
INK_SOFT = "#4A4A44" if THEME == "light" else "#B8B7B0"
INK_MUTED = "#6B6A63" if THEME == "light" else "#A8A79F"
GRID = "rgba(26,26,23,0.15)" if THEME == "light" else "rgba(240,239,232,0.15)"
# Imprint categorical palette
BRAND = "#009E73" # position 1 — observations (first series, always)
MODEL_COLOR = "#C475FD" # position 2 — transit model
# Data
np.random.seed(42)
n_points = 500
phase = np.sort(np.random.uniform(0.0, 1.0, n_points))
# Transit model parameters (quadratic limb darkening)
transit_center = 0.5
transit_duration = 0.06
transit_depth = 0.01
u1, u2 = 0.4, 0.2
# Compute model flux with limb-darkened transit shape
model_flux = np.ones_like(phase)
in_transit = np.abs(phase - transit_center) < transit_duration
z = np.abs(phase[in_transit] - transit_center) / transit_duration
mu = np.sqrt(1 - z**2)
limb_darkening = 1 - u1 * (1 - mu) - u2 * (1 - mu) ** 2
transit_profile = 1 - transit_depth * limb_darkening
model_flux[in_transit] = transit_profile
# Observed flux with noise
flux_err = np.random.uniform(0.0008, 0.0020, n_points)
flux = model_flux + np.random.normal(0, 1, n_points) * flux_err
# Fine model curve for smooth overlay
phase_model_fine = np.linspace(0, 1, 2000)
model_fine = np.ones_like(phase_model_fine)
in_transit_fine = np.abs(phase_model_fine - transit_center) < transit_duration
z_fine = np.abs(phase_model_fine[in_transit_fine] - transit_center) / transit_duration
mu_fine = np.sqrt(1 - z_fine**2)
ld_fine = 1 - u1 * (1 - mu_fine) - u2 * (1 - mu_fine) ** 2
model_fine[in_transit_fine] = 1 - transit_depth * ld_fine
# Plot
fig = go.Figure()
fig.add_trace(
go.Scatter(
x=phase,
y=flux,
mode="markers",
name="Observations",
marker={"size": 8, "color": BRAND, "opacity": 0.55, "line": {"width": 0.5, "color": PAGE_BG}},
error_y={
"type": "data",
"array": flux_err,
"visible": True,
"color": "rgba(0,158,115,0.35)",
"thickness": 1.5,
"width": 0,
},
hovertemplate="Phase: %{x:.4f}<br>Flux: %{y:.5f}<extra></extra>",
)
)
fig.add_trace(
go.Scatter(
x=phase_model_fine,
y=model_fine,
mode="lines",
name="Transit Model",
line={"color": MODEL_COLOR, "width": 3},
hovertemplate="Phase: %{x:.4f}<br>Model: %{y:.5f}<extra></extra>",
)
)
# Transit window highlight
fig.add_vrect(
x0=transit_center - transit_duration,
x1=transit_center + transit_duration,
fillcolor="rgba(196,117,253,0.06)",
line_width=0,
annotation_text="Transit Window",
annotation_position="top",
annotation_font={"size": 13, "color": INK_MUTED},
)
# Baseline reference line
fig.add_hline(y=1.0, line_dash="dot", line_color=GRID, line_width=1.5)
# Transit depth annotation
min_model = 1 - transit_depth
fig.add_annotation(
x=transit_center + transit_duration + 0.025,
y=(1.0 + min_model) / 2,
text=f"Depth: {transit_depth * 100:.1f}%",
showarrow=False,
font={"size": 16, "color": INK_SOFT},
bgcolor=ELEVATED_BG,
borderpad=4,
)
# Bracket lines for transit depth
bracket_x = transit_center + transit_duration + 0.015
fig.add_shape(type="line", x0=bracket_x, x1=bracket_x, y0=1.0, y1=min_model, line={"color": INK_SOFT, "width": 1.2})
fig.add_shape(
type="line", x0=bracket_x - 0.005, x1=bracket_x + 0.005, y0=1.0, y1=1.0, line={"color": INK_SOFT, "width": 1.2}
)
fig.add_shape(
type="line",
x0=bracket_x - 0.005,
x1=bracket_x + 0.005,
y0=min_model,
y1=min_model,
line={"color": INK_SOFT, "width": 1.2},
)
# Ingress/egress contact markers
for label, xpos in [("T₁", transit_center - transit_duration), ("T₄", transit_center + transit_duration)]:
fig.add_annotation(x=xpos, y=min_model - 0.0015, text=label, showarrow=False, font={"size": 14, "color": INK_MUTED})
# Title length 69 chars → ratio 67/69 ≈ 0.97 → rounds to 16px (at default floor)
title = "Exoplanet Transit · lightcurve-transit · python · plotly · anyplot.ai"
# Style
fig.update_layout(
autosize=False,
title={"text": title, "font": {"size": 16, "color": INK}, "x": 0.5, "xanchor": "center"},
xaxis={
"title": {"text": "Orbital Phase", "font": {"size": 12, "color": INK}},
"tickfont": {"size": 10, "color": INK_SOFT},
"showgrid": False,
"showline": False,
"zeroline": False,
"range": [-0.02, 1.02],
"linecolor": INK_SOFT,
"spikemode": "across",
"spikethickness": 1,
"spikecolor": GRID,
"spikedash": "dot",
},
yaxis={
"title": {"text": "Relative Flux", "font": {"size": 12, "color": INK}},
"tickfont": {"size": 10, "color": INK_SOFT},
"showgrid": True,
"gridcolor": GRID,
"gridwidth": 1,
"showline": False,
"zeroline": False,
"linecolor": INK_SOFT,
"spikemode": "across",
"spikethickness": 1,
"spikecolor": GRID,
"spikedash": "dot",
},
hoverdistance=20,
hovermode="closest",
legend={
"font": {"size": 10, "color": INK_SOFT},
"x": 0.02,
"y": 0.02,
"xanchor": "left",
"yanchor": "bottom",
"bgcolor": ELEVATED_BG,
"bordercolor": INK_SOFT,
"borderwidth": 1,
},
paper_bgcolor=PAGE_BG,
plot_bgcolor=PAGE_BG,
font={"color": INK},
margin={"l": 80, "r": 40, "t": 80, "b": 60},
)
# Save — 3200×1800 landscape (width=800 × scale=4)
fig.write_image(f"plot-{THEME}.png", width=800, height=450, scale=4)
fig.write_html(f"plot-{THEME}.html", include_plotlyjs="cdn", config={"displayModeBar": True, "scrollZoom": True})
Part of Astronomical Light Curve on anyplot.ai.