Glossary
Quick reference to the terms, scales and data used across the IPMA platform.
Astronomical terms related to the position of the Sun and Moon. Data is computed locally using the suncalc-php library, not from the IPMA API.
Solar Twilight Phases
| Term | Description |
|---|---|
| Astronomical dawn | Sun at −18° (sky completely dark before sunrise) |
| Nautical dawn | Sun at −12° (horizon just visible) |
| Civil dawn | Sun at −6° (enough light for outdoor work) |
| Sunrise | Upper limb touches horizon |
| Sunrise end | Lower limb clears horizon (full disc visible) |
| Golden hour end | Sun below 6° (warm, low-angle light) |
| Solar noon | Sun at highest altitude for the day |
| Sunset | Upper limb touches horizon at dusk |
| Sunset start | Lower limb clears horizon (full disc set) |
| Golden hour start | Sun below 6° (warm, low-angle light) |
| Civil dusk | Sun at −6° (enough light for outdoor work) |
| Nautical dusk | Sun at −12° (horizon just visible) |
| Astronomical dusk | Sun at −18° (sky completely dark after sunset) |
| Nadir | Sun at its lowest point (directly below) |
| Day length | Interval from sunrise to sunset |
Sun Position
| Term | Description |
|---|---|
| Azimuth | Compass bearing (0° = North, 90° = East, etc.) |
| Altitude | Angle above the horizon (negative = below horizon) |
Moon Phases (Numeric Range 0–1)
| Phase | Range |
|---|---|
| New moon | 0–0.125 |
| Waxing crescent | 0.125–0.25 |
| First quarter | 0.25–0.375 |
| Waxing gibbous | 0.375–0.5 |
| Full moon | 0.5–0.625 |
| Waning gibbous | 0.625–0.75 |
| Last quarter | 0.75–0.875 |
| Waning crescent | 0.875–1 |
Additional Moon Data
| Term | Description |
|---|---|
| Moonrise | Time of Moon's appearance above the horizon |
| Moonset | Time of Moon's disappearance below the horizon |
| Illumination | Percentage of lunar surface illuminated |
| Distance | Distance of the Moon in kilometres |
| Azimuth (Moon) | Compass bearing of the Moon (0° = North, 90° = East, etc.) |
| Altitude (Moon) | Angle of the Moon above the horizon |
Planet Parameters
Data for the seven classical planets (Mercury through Neptune). Calculated locally using simplified astronomical algorithms.
| Parameter | Description |
|---|---|
| RA (Right Ascension) | Equatorial coordinate analogous to longitude, measured in hours (0–24h) |
| Dec (Declination) | Equatorial coordinate analogous to latitude (−90° to +90°) |
| Azimuth | Compass bearing (0° = North, 90° = East, 180° = South, 270° = West) |
| Altitude | Angle above horizon; positive = visible, negative = below horizon |
| Magnitude | Apparent brightness; lower numbers are brighter (Venus ~−4, Neptune ~+8) |
| Elongation | Angular separation from the Sun (0° = behind Sun, 180° = opposite) |
| Distance | Distance from Earth in astronomical units (AU) and kilometres |
Terms related to the sea-state forecast provided by the IPMA API.
| Term | Description | Unit |
|---|---|---|
| Wave height | Significant wave height of wind-generated waves (average of the highest one-third) | m |
| Wave period | Dominant period between successive wave crests | s |
| Wave direction | Compass direction waves are travelling toward | compass |
| Total sea | Combined height of swell and wind-generated waves | m |
| SST (Sea Surface Temperature) | Temperature of water at the surface | °C |
The “feels like” temperature shown next to station readings. It is computed locally from each station’s observation, not supplied by the IPMA API.
It uses Steadman’s apparent-temperature scale (Steadman 1984, refined 1994) in its simplified operational form — an approximation of his full model of heat balance in the human body.
The model represents an adult walking outdoors in the shade, so the result does not account for direct sunlight: a station in full sun will feel hotter than the value shown. A variant of the formula also takes solar radiation into account; it is not used here, because not every station reports radiation.
Formula
e = (RH / 100) × 6.105 × exp(17.27 × T / (237.7 + T))
AT = T + 0.33 × e − 0.70 × v − 4.00| Symbol | Meaning | Unit |
|---|---|---|
T |
Measured air temperature | °C |
RH |
Relative humidity | % |
e |
Water-vapour pressure, derived from T and RH | hPa |
v |
Wind speed at 10 m | m/s |
AT |
Apparent temperature | °C |
How humidity and wind pull it
Humidity raises the result, because moist air slows evaporative cooling from the skin. Wind lowers it, because moving air carries heat away. The two act independently, so they can cancel each other out entirely:
| Air temp. | Humidity | Wind | Feels like |
|---|---|---|---|
| 25 °C | 40 % | calm | 25.2 °C +0.2 |
| 25 °C | 90 % | calm | 30.4 °C +5.4 |
| 25 °C | 40 % | 8 m/s | 19.6 °C −5.4 |
| 25 °C | 90 % | 8 m/s | 24.8 °C −0.2 |
Why barometric pressure is not used
The e term is the partial pressure of water vapour, fixed by temperature and relative humidity alone. It is not the station’s barometric pressure, which has no term in this formula — so a station’s pressure reading never changes its apparent temperature.
Missing readings
- Temperature and humidity are both required. Without either, no value is shown (—).
- Where wind is unreported it is treated as calm and the value is marked ≈. Because the wind term is subtracted, such a value is an upper bound — the true figure is lower by 0.70 × the unreported speed in m/s.
- A wind speed measured as zero is real data, not an assumption, and is shown without the ≈ marker.
- On the 24-hour trend chart, hours plotted from an assumed calm are drawn as hollow points.
WHO global UV index scale, used by IPMA.
| Level | Range | Advice |
|---|---|---|
| Low | 0–2 | No protection required. |
| Moderate | 3–5 | Protection recommended: hat, sunglasses, SPF 30+. |
| High | 6–7 | Avoid sun 11h-16h; SPF 30+, shade, clothing. |
| Very High | 8–10 | Extra protection; avoid being outside 11h-16h. |
| Extreme | 11+ | Stay indoors during midday; full protection outdoors. |
Status of harvesting availability in bivalve mollusc production zones. Note: Zones may have interdicted species even when the overall status is "open".
| Status | Description |
|---|---|
| Open | Harvesting permitted for all species. |
| Partially open | Harvesting permitted for some species; others interdicted. |
| Partially closed | Harvesting restricted; some species interdicted. |
| Closed | Harvesting prohibited for all species. |
| Unknown | Status not available. |
EU Sanitary Classification
Classifications follow EU bivalve sanitary standards:
- A: Ready for direct consumption
- B: Depuration required
- C: Relaying required
- NA: Not applicable