The map type pop-up, located at the top right corner, let you toggle between the map types:
When they exist, the northern and southern path limits are rose and the central line is blue. The orange lines crossing the path indicate the position of maximum eclipse at 10-minute intervals. When displayed the curves delimiting the penumbral area, of maximum eclipse on the horizon and of equal magnitude are all in green; and maximum eclipse at sunrise and sunset is in yellow. When displayed the curves of maximum eclipse at 30-minute intervals are displayed in violet.
- "Map" displays cartographic features on the map (roads when available, rivers, etc).
- "Terrain", available when "Map" is selected, displays physical features on the map, such as mountains and vegetation, with elevation shading. To enable this option first select "Map".
- "Satellite" (default) loads an aerial or satellite image of selected area.
- "Legend", available when "Satellite" is selected, displays major roads and features overlaid.
- "Night Lights" displays a night view showing the light pollution using data from the NASA Blue Marble Earth 2012 'beautified'.
- "Night Sky Brightness" displays a night view of the sky brightness using data from the World Atlas of the Artificial Night Sky Brightness 2006 by David Lorenz.
Note for the "Night Lights" map type:
This overlay of the Earth at night is a composite assembled from data acquired by the Suomi National Polar-orbiting Partnership (Suomi NPP) satellite over nine days in April 2012 and thirteen days in October 2012.
The nighttime view of Earth was made possible by the Visible Infrared Imaging Radiometer Suite. VIIRS detects light in a range of wavelengths from green to near-infrared and uses filtering techniques to observe dim signals such as gas flares, auroras, wildfires, city lights, and reflected moonlight.
Away from the cities, much of the nightlight observed by Suomi NPP is wildfire. In other places, fishing boats, gas flares, lightning, oil drilling, or mining operations can show up as points of light. The number of rural lights is also a function of composite imaging. Fires and other lighting could have been detected on any one day and integrated into the composite picture even though they were temporary. That seems to be the case in the Northern Territory, Western Australia and the northwest corner of South Australia, where many lights appear in this map. Different areas burned with wildfire at different times that the satellite passed over, giving the impression (in the composite view) that the entire area was lit up at once. See City Lights of Australia, or Not for a more detailed explanation.
A click anywhere inside the penumbral area of the eclipse will display a tooltip with the local circumstances. At the same time the (ant-)umbral shadow outline will be displayed at the local maximum eclipse if the click is inside the path, i.e. inside the area swept by the (ant-)umbral shadow. When hovering the cursor over the various contact events the position of the shadow outline will be recomputed at the current contact time.
- Eclipse type & Duration - The type and duration of the eclipse as seen at your location (taking into account that the Sun may not be above the horizon until the eclipse is in progress, etc.). The corrected duration taking into account the lunar limb profile is displayed only inside the path of totality. Displays "???" if the eclipse is underway at sunrise or sunset,
- Umbral/Antumbral depth - The percentage of the way from the closest edge of the eclipse path to the centre line that this location is at,
- Path Width - The width of the total or annular path in kilometers,
- Obscuration - The percentage of the Sun’s disk surface covered at maximum eclipse (this box will display "???" if the Sun is below the horizon at maximum eclipse),
- Magnitude at maximum - The fraction of the Sun’s diameter covered by the Moon at the local maximum eclipse,
- Moon/Sun size ratio - The ratio of the apparent size of the Moon to that of the Sun at the local maximum eclipse,
- Umbral/Antumbral velocity - The speed of the umbra/antumbra,
- Eclipse diagram - The eclipse diagram displays the relatives positions of the Sun, Moon and ground in horizontal coordinates (the refraction and terrain declivity are not taken into account). The solar north is indicated by the red tick mark and the diagram is updated when hovering the cursor over the various contact events.
- Eclipse Event or sunrise/sunset,
- The Universal Time (UT) Date and Time of the event. When the event occurs while the Sun is below the horizon, an asterisk (*) will appear after the hour. The given time is provided without any lunar limb correction, to know the time with the limb correction just add the value found in the LC column. Be aware that the computations are executed using the standard IAU 1976 solar radius, that is 959.63 arc-seconds at one astronomical unit, and not the true photospheric solar radius that is closer to 959.98 arc-seconds at one astronomical unit (±0.02 arc-second),
- Alt - Altitude of the sun, in degrees, above the horizon. To have the value with the atmospheric refraction, hover the cursor over the value for a few seconds to get a tooltip,
- Azi - Azimuth of the sun, in degrees (0° = due north, 90° = due east, etc.),
- P - Angle, in degrees, between the north point on the Sun’s disk and the contact point with the Moon. When the current event is sunrise or sunset, the obscuration of that event is displayed over the two columns when the eclipse is in progress (the time is then rounded to the nearest minute and the atmopsheric refraction not taken into account),
- V - The "o’clock" position on the Sun’s face of the contact point with the Moon (eg V=12.0 means that the contact point is in the "12 o’clock" position - ie the top of the Sun’s disk),
- LC - The calculator is able to determine a correction factor to the time of the start and end of the eclipse due to the fact that the Moon’s limb is not smooth. When it is, then the correction (in seconds) is given. A click on the LC column header will display the lunar limb profile and Baily’s beads in a new window.
All the tools can be activated by clicking on their respective icon. Plus one more click to deactivate them.
The "timezone" tool will give you the time offset needed to compute local time at the observer’s location.
The "road traffic" tool will indicate you the current state of the road traffic. The road traffic can be activated by default when loading the map by just appending &Traffic=1 to the URL.
The elevation profile in the maximum eclipse line of sight is there to let you make sure the eclipse will be visible over the horizon. To compute it, first click on the "elevation" tool to activate and then click at the observer’s location.
The Δmin value is the minimum height between the bottom of the solar disk and the terrain. If negative, then part of the eclipse will not be visible (the apparent diameter of the Sun is roughly half a degree). The day and night areas can be activated by default when loading the map by just appending &ND=1 to the URL.
The "day and night" tool will let you display areas where the Sun is set at the given time from the observer’s location. The areas if civil twilight, nautical twilight, astronomical twilight and night are all shaded appropriately. When hovering the cursor over the various contact events the display will be updated to show the situation at the contact event time. The elevation profile can be activated by default when loading the map by just appending &EP=1 to the URL.
When activated the "geolocation tracking" tool will constantly center the map on the observer’s location while displaying the local eclipse circumstances. When zooming far enough you can visualize around your location the 95% confidence circle indicating the accuracy of your geolocation: the smaller the radius is the better is your location known. To work this feature needs you to allow geolocation: please refer to your browser’s privacy settings; your operating system may also have some geolocation privacy settings. Please take note that no data is transmitted or stored on the server generating the map.
Various techniques —GPS (cellphones), triangulation GSM/3G/4G/LTE (cellphones), Wi-Fi triangulation (cellphones and MAC address databases), IP address (correspondence with databases)— are put to use for more or less accurate geolocation. Over time they can be combined to refine the result. Some methods such as GPS are slower than others and more energy-intensive especially on cellphones. That is why the first step is often to get a rough approximation —often by GSM triangulation— and then start up the GPS module after a few seconds (this is visualized on iOS by the gradual decrease of the extent of blue circle).
The geolocation can be activated by default when loading the map by just appending &GL=1 to the URL.
- Those computations do not account for atmospheric refraction, which makes a difference if the eclipse occurs close to sunrise or sunset (a good example of this was the midnight Sun eclipse in Antarctica on November 23, 2003). However, by hovering the cursor over the altitude value a tooltip will show the correction with refraction,
- Corrections for the irregular lunar limb are only available when you are online, i.e. connected to the Internet. This can produce a few seconds time difference on the start and end of totality or annularity,
- It is not possible to predict the exact value of ΔT in advance, although the extrapolated value should be good to better than 0.5 seconds.
Thanks to Sergey and Larry for making regular and timely imagery updates to locations where eclipse chasers will be going.