Overview
The Moon Simulator in TPE (The Photographer’s Ephemeris) Web provides a detailed, interactive view of the Moon as seen from your selected map location. It is synchronised with the time slider and map view, allowing you to explore lunar phase, orientation, libration, and (when applicable) eclipse geometry.
Prefer a video? Watch the intro video:
Using the Moon Simulator
When in map view, the Moon Simulator typically appears at the top-right of the map whenever the Moon is within 5° of the horizon or above it. However, if the Moon is not selected as a displayed body, or if you have chosen to hide the Moon and Eclipse Simulators, it won’t appear at all.
You can minimise it (button at the top-left, shown above):
Or you can expand it to a full-screen view:
Key Features
The Moon Simulator supports the following features:
- Real-time rendering of the Moon with accurate phase, libration, and position
- Lunar feature labels (mare, craters) with level-of-detail filtering based on zoom
- Camera controls with azimuth/altitude gauges and double-click reset
- Playback controls for time animation with multiple speed options
- Display options toolbar (sky gradient, labels, shadow rings, horizon)
- Lunar eclipse Earth shadow visualisation with umbra/penumbra cones
- Lunar eclipse contact time buttons (P1, U1, U2, Max, U3, U4, P4)
- Below-horizon indicator when Moon is not visible
- Camera direction overlay showing azimuth and altitude
- Day navigation controls for quick date changes
- Lunar distance and libration data display
- Mini 3D Moon preview in simulator popup on map
- Solar eclipse redirect message when viewing during a solar eclipse
Playback Controls
The state of the Moon reflects the selected date and time and the primary pin position on the map: everything is calculated from those key inputs.
If you adjust the time of day using the time slider, you’ll see the appearance of the Moon change. If you move the pin position on the map, you won’t affect things like the illuminated fraction of the Moon, but the orientation with respect to the observer will change (due to the parallactic angle).
In addition, you can use the playback controls at the lower left of the full simulator screen to play/pause the evolving state of the Moon over time. Choose from one of the available playback speeds (×60, ×300, ×900), corresponding to one second equalling one minute, five minutes, or 30 minutes, respectively.
You can skip forward or back five minutes at a time using the arrow buttons either side of the time display, or one day back or forward using the buttons either side of the date.
Horizon
When the Moon is near the horizon:
- A horizontal Horizon mask covers the portion of the lunar disc below the local horizon.
- As the Moon rises, the mask gradually reveals the disc.
- As the Moon sets, the mask progressively covers it.
This mask represents the true local horizon at the selected map location.
Labels and Surface Features
You can toggle Labels on or off.
When enabled, labels identify selected lunar features, including:
- Major maria (dark basalt plains)
- Prominent craters
- Apollo landing sites
- Selected limb features
The simulator is not a complete lunar atlas, but it includes key features useful for orientation and planning.
The tool can also help identify phase-dependent features such as the “ Luna X ” and “ Luna V, ” which become visible near first quarter when low-angle sunlight highlights specific crater rims.
Changing the View
You can control the Moon display:
- Use a mouse wheel, a two-finger trackpad gesture, or a pinch gesture to zoom in or out
- Click/tap and drag to pan the Moon around the display (this can be useful at high zoom levels to bring different areas of the lunar limb into view)
- Double-click/tap anywhere to reset the camera to a default zoom, centred view
Lunar Information
The playback control panel includes additional information about the current state of the Moon. What is displayed varies based on the selected display mode and circumstances.
Distance and Relative Size
The simulator displays the current Earth–Moon distance. Because the Moon’s orbit is elliptical (not perfectly circular), its distance varies over time. This affects its apparent angular size in the sky.
The simulator indicates:
- The current distance
- The percentage difference relative to the Moon’s average angular size
For example, a value of −3% means the Moon appears 3% smaller than its average apparent size.
Orientation Modes
The simulator supports three orientation modes: Zenith Up, Lunar North Up and Celestial North Up.
Zenith Up
This is the default view.
The Moon is oriented as it would appear to an observer standing at your selected location and looking upwards. The top of the display corresponds to the observer’s zenith (the point directly overhead).
Lunar North Up
In this mode, the Moon is rotated so that its north pole is at the top of the screen.
This view highlights libration, which is the apparent “ wobble ” of the Moon caused by variations in its orbit and axial tilt. Libration allows observers to see slightly more than 50% of the Moon’s surface over time.
The simulator displays:
- Libration in latitude (north–south tilt)
- Libration in longitude (east–west shift)
This is useful for photographers tracking features that become visible only under specific libration conditions.
Celestial North Up
In this mode, the top of the screen corresponds to celestial north (the north direction on the sky’s coordinate system).
The simulator displays:
- Position angle (the orientation of the Moon’s axis relative to celestial north)
- Parallactic angle (the rotation of the Moon’s apparent orientation due to the observer’s location on Earth)
These values are useful when aligning or correcting the rotation of lunar photographs.
Disabling the Simulator
You can disable the Moon Simulator entirely:
- Open Settings
- Check Hide Moon and Solar Eclipse Simulators
- Click Save
The simulator will no longer appear automatically until re-enabled.
Subscription Access
Access to the Moon Simulator follows TPE Web subscription tiers:
- PRO: Full access
- Supporter: 5-day look-ahead
- Free users: 24-hour look-ahead
Look-ahead limits apply to date navigation and eclipse exploration.
Credits
- 3D model textures: NASA’s Scientific Visualization Studio
