ToolLiveCited
How far am I from the aurora?
Answer
The nearest 10% cell is 3,839 km NW of Minneapolis, beyond the 1000 km that SWPC gives for seeing a bright display.
OVATION observed 10:53 UTC, forecast 12:26 UTC, 93 min lead. Distances are great-circle from 44.98°N 93.26°W to cell centers.
Worked example
Seattle sits at 47.61N 122.33W. On this request the nearest cell at 10% or more is centered at 66N 145W, reading 10%. It lies 2,437 km (1,514 mi) away on an initial bearing of 335 degrees, roughly NNW.
The bearing is the direction to face when you start walking the great circle, measured clockwise from true north. For aurora it tells you which part of the horizon to watch. A bearing near 0 or 360 means due north.
How the distance is measured
Glow's server reads the full live OVATION grid, about 65,000 cells, and keeps only the cells at or above each threshold. For each threshold it computes the great-circle distance from your coordinates to every remaining cell center with the haversine formula on a sphere of radius 6,371 km, and keeps the shortest. Then it computes the initial compass bearing to that cell.
The three thresholds answer three questions. The 10% cell is the nearest fringe of the oval that the model sees. The 30% and 50% cells are the nearest parts of its brighter core. When all three sit far away, the oval is quiet or far north.
Your coordinates are rounded to 2 decimals, about 1 km, before they leave the browser. The grid never ships to the page; only the three nearest cells come back.
Comparing with SWPC's 1000 km
SWPC says bright aurora can be observed from as far as 1000 km away when conditions are right. Its viewing tips give the same limit as 600 miles and name the conditions: a high vantage point and an open view toward the north.
Glow's verdict line compares the 10% distance with that 1000 km. Inside it, the fringe of the oval is within the range SWPC describes for a bright display. Beyond it, even a bright display over that cell would sit below your horizon by SWPC's own rule of thumb.
The comparison is geometric. It does not know how bright the display is, and a 10% cell is the faint fringe, not the bright core. Read the 30% and 50% rows for the brighter parts.
Limits
OVATION cells are 1 degree square, so distances carry up to about 80 km of rounding at the cell level. The model covers the next 30 to 90 minutes only. Clouds, twilight and the moon are outside this tool; the chance tool shows darkness and US cloud for the same coordinates.
When the NOAA feed is older than 2 hours, every row is blank. When a threshold has no cell anywhere, its row says so.
Questions
- How far away can you see the northern lights?
- SWPC gives 1000 km (600 miles) for a bright display seen from a high point with an open northern horizon. Glow uses that figure as the comparison line and labels it a best case.
- Why measure to the nearest cell rather than straight north?
- The oval is tilted toward the geomagnetic pole, so the nearest part can sit northwest or northeast of you. The bearing column shows which way.
- What does it mean when no cell reaches 50%?
- The live model has no cell that high anywhere on the grid. The row says so instead of reporting a distance to a weaker cell.
- Does a short distance mean I will see the aurora?
- No. It means the modeled oval is near. Darkness, cloud, moonlight and city lights still decide what you see.
- Why is the distance different from a Kp map?
- A Kp map draws a typical line for a planetary index level. This tool reads the current OVATION cells, so the distance follows the real oval.