Find Heliacal Events

Use the /v1/heliacal endpoint to find when a planet emerges from or disappears into the Sun's glare. This requires an observer location since visibility depends on the local horizon and atmosphere.

Find Venus's heliacal rising

The heliacal rising ("morning first") is when a planet first becomes visible in the pre-dawn sky:

curl "https://api.morphemeris.com/v1/heliacal?\
datetime=2024-01-01T00:00:00Z\
&body=venus\
&event=morning_first\
&lat=40.7128\
&lon=-74.006" \
  -H "Authorization: Bearer morphemeris_live_YOUR_KEY"

The response tells you exactly when Venus becomes visible, the angular separation from the Sun, and both altitudes:

const { data } = await res.json();
console.log(`Venus rises heliacally on ${data.event_datetime}`);
console.log(`Sun-Venus arc: ${data.visibility_arc_deg.toFixed(1)}°`);
console.log(`Sun altitude: ${data.sun_altitude.toFixed(1)}° (below horizon)`);
console.log(`Venus altitude: ${data.object_altitude.toFixed(1)}° (above horizon)`);

Model different conditions

The defaults assume standard atmosphere and normal naked-eye vision. Override them for specific scenarios:

High-altitude desert observatory

curl "https://api.morphemeris.com/v1/heliacal?\
datetime=2024-01-01T00:00:00Z\
&body=mars\
&event=morning_first\
&lat=31.9583\
&lon=-111.5967\
&alt=2096\
&pressure_mbar=790\
&temp_celsius=10\
&humidity_pct=20" \
  -H "Authorization: Bearer morphemeris_live_YOUR_KEY"

Lower pressure and humidity at altitude mean clearer skies — the planet may become visible earlier than at sea level.

Telescope observation

curl "https://api.morphemeris.com/v1/heliacal?\
datetime=2024-01-01T00:00:00Z\
&body=saturn\
&event=morning_first\
&lat=40.7128\
&lon=-74.006\
&telescope_aperture_cm=20\
&telescope_magnification=50" \
  -H "Authorization: Bearer morphemeris_live_YOUR_KEY"

Available events

Tips

• Heliacal searches cost 3 credits.
• Observer location (lat, lon) is required — there's no "global" mode for heliacal events.
• The Sun and Moon cannot have heliacal events. Outer planets (Jupiter through Pluto) cannot have evening_first or morning_last.
• Results are sensitive to atmospheric parameters. If you're modeling historical observations, consider the local climate.
• See Heliacal Events for background on the visibility model and planetary cycles.