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Comet C/2025 A6 (Lemmon) - October 2025

Plot

Path of Comet C/2025 A6 (Lemmon) - October 2025 SVG / PNG

How to See It

  • 📅 When: October 21-31, 2025 just after sunset
  • 🌎 Where (on Earth): Visible from Northern Hemisphere
  • 👀 Where (in the sky): Look west
  • 🔭 What you need: binoculars or a small telescope
  • Arcturus is one of the brightest stars in the sky, so use that as a guide
  • Antares is a bright reddish-orange star, another great guiding star
  • Bootes is also a very easy constellation to see — it looks like a kite

On October 21, 2025 the comet C/2025 A6 (Lemmon) will make its closest approach to Earth, becoming bright enough to see with binoculars or maybe even your naked eye. Look for it in the constellation Bootes just after sunset. It should be easily visible until at least the end of October. You can use the chart above to figure out where it'll be each day.

Source Code

Python 3.12 Starplot 0.16.5 
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from datetime import datetime, timedelta
from zoneinfo import ZoneInfo

from skyfield.api import load
from skyfield.data import mpc
from skyfield.constants import GM_SUN_Pitjeva_2005_km3_s2 as GM_SUN

from starplot import (
    HorizonPlot,
    PlotStyle,
    style_extensions,
    Constellation,
    Observer,
    _,
)

# First, we use Skyfield to get comet data
# Code adapted from: https://rhodesmill.org/skyfield/kepler-orbits.html#comets
with load.open(mpc.COMET_URL) as f:
    comets = mpc.load_comets_dataframe(f)

# Keep only the most recent orbit for each comet, and index by designation for fast lookup.
comets = (
    comets.sort_values("reference")
    .groupby("designation", as_index=False)
    .last()
    .set_index("designation", drop=False)
)

# Find Comet C/2025 A6 (Lemmon)
# Values at time of publishing (2025-OCT-15):
# CK25A060  2025 11  8.5383  0.529888  0.995631  132.9700  108.0979  143.6635  20251013  13.2  4.0  C/2025 A6 (Lemmon)
row = comets.loc["C/2025 A6 (Lemmon)"]

# Load timescale and ephemeris
ts = load.timescale()
eph = load("de421.bsp")
sun, earth = eph["sun"], eph["earth"]
comet = sun + mpc.comet_orbit(row, ts, GM_SUN)

# October 17 @ 6:30pm PT (about 20min after sunset)
tz = ZoneInfo("US/Pacific")
dt = datetime(2025, 10, 17, 18, 30, 0, 0, tzinfo=tz)

# Find the RA/DEC of comet for every other day starting on October 17, 2025
radecs = []
for day in range(0, 22, 2):
    dt_current = dt + timedelta(days=day)
    t = ts.from_datetime(dt_current)
    ra, dec, distance = earth.at(t).observe(comet).radec()
    radecs.append((dt_current, ra.hours * 15, dec.degrees))

# Now let's plot the data on a map!
style = PlotStyle().extend(
    style_extensions.BLUE_DARK,
    style_extensions.GRADIENT_BOLD_SUNSET,
    style_extensions.MAP,
)

# Create observer for October 21 @ 6:30pm PT (about 20min after sunset)
observer = Observer(
    dt=datetime(2025, 10, 21, 18, 30, 0, 0, tzinfo=tz),
    lat=33.363484,  # Palomar Mountain, CA
    lon=-116.836394,
)

p = HorizonPlot(
    altitude=(0, 55),
    azimuth=(220, 320),
    observer=observer,
    style=style,
    resolution=3000,
    scale=1,
    hide_colliding_labels=False,
)

# Plot the comet markers
for t, ra, dec in radecs:
    label = f"{t.month}/{t.day}"
    p.marker(
        ra=ra,
        dec=dec,
        style={
            "marker": {
                "size": 38,
                "symbol": "comet",
                "fill": "full",
                "color": "hsl(183, 100%, 80%)",
                "edge_color": "hsl(183, 100%, 80%)",
                "alpha": 1,
                "zorder": 4096,
            },
            "label": {
                "anchor_point": "top right",
                "font_size": 28,
                "font_weight": "bold",
                "font_color": "hsl(60, 70%, 72%)",
                "zorder": 4096,
                "offset_x": "auto",
                "offset_y": "auto",
            },
        },
        label=label,
    )

boo = Constellation.get(iau_id="boo")

p.horizon()

p.constellations(where=[_.iau_id.isin(["boo"])], style__alpha=0.75, style__width=1.8)

p.stars(
    where=[_.hip.isin(boo.star_hip_ids) | (_.name == "Antares")],
    where_labels=[_.magnitude < 2],
    style__label__font_size=30,
)

p.constellation_labels(style__font_alpha=1)

p.export("plot.svg", format="svg")