Using these programs, you can view the moon in fine detail from four different sides as through a virtual telescope, illuminated at any relative phase angle from 0 to ±360 degrees as well as the current phase, to the nearest degree, based on the NASA/JPL DE405 ephemeris model.
On initial startup of any of the programs below, the current lunar phase, as viewed from the selected perspective, is displayed. After that, you can set the view to any selected phase angle you want or let the program select a random phase.
Due to the large sizes of the lunar phase images (1500x1500 pixels), they will attempt to display in a separate tab or window. The phase images are in PNG format and rendered against a transparent background. The programs also work well with browsers that have a zoom feature (tested in Internet Explorer and Firefox).
In terms of 3D perspective, the lunar surface was rendered as if viewed from a mean geocentric distance of 384401 km (238856 mi) and mangified as through geocentric telescope. An image of the telescopic moon (magnified 100x) from Earth does not look quite the same as the view from 1/100th of the normal lunar distance. The closer we get to the moon, the less we can see of its visible surface, but the clarity of the image detail within that limited view increases in quality or resolution.
- North is upward.
- Near Side Lunar Phase Explorer
This program shows the normal or near-side face of the moon at any given phase angle. It simulates a telescopic, high-resolution geocentric view of the moon at its mean distance.
- Far Side Lunar Phase Explorer
This program shows the far-side of the moon at any given relative phase angle. Here, we have a view from behind the moon looking back as if viewed from an imaginary Earth on the opposite side at the same distance from the moon.
East (sky) Side Lunar Phase Explorer
This program shows the east (sky) side of the moon at any given relative phase angle. Here, we see the moon as viewed from the left side or centered over the western lunar hemisphere.
- West (sky) Side Lunar Phase Explorer
This program views the west (sky) side of the moon at any given relative phase angle, showing the moon as viewed from the right side or centered over the eastern lunar hemisphere.
- Whatever the lunar phase we view from Earth, an observer on the moon looking back would see Earth at the opposite phase ((Front lunar phase + 180°) mod 360) in the lunar sky. For example, if we see the moon in first quarter phase from Earth, an observer on the moon would see Earth illuminated in last quarter phase.
|THE LUNAR PHASE EXPLORER PROGRAM INTERFACE
Using the programs is relatively intuitive and the interface consists of a single input box and seven buttons as shown here.
- Basically, you simply enter an integer phase angle and click
[Compute] to display a view of the moon illuminated at the specified phase. North is upward. The lunar view can be centered on the near-side (normal front view) or far-side or over the eastern or western hemispheres.
- The phase angle is taken to be the difference between the geocentric ecliptical longitudes of the moon and sun in the context moon minus sun and adjusted to fall in the range from 0 to +360 degrees. This becomes the position angle of the sun on the phase circle as shown in the phase legend shown below.
JDTT = JD (Julian Date) value at 12-hour intervals
Lm = Geocentric ecliptical longitude of the Moon
Ls = Geocentric ecliptical longitude of the Sun
PhaseDeg = Lunar phase angle
This algorithm will compute the lunar phase angle in the
range from 0 to +360 degrees, from the (Lm, Ls) values.
w = 360 - Lm + Ls
if w > 360 then w = w - 360
PhaseDeg = 360 - w
RELATIVE PHASE ANGLE LEGEND
First Quarter 90°
Last Quarter 270°
A Quick Synopsis of the Interface Buttons
[-] and [+] buttons will correspondingly decrement or increment the currently displayed phase by one degree. This way you can move through the phases backward or forward, one degree at a time sequentially, from any arbitrary starting point. Due to the large image sizes, just how smoothly this works ultimately depends on your browser, cache settings and ISP connection type, speed and quality.
[Mirror Phase] button toggles between mirror images of the phase illumination. If the right side is a crescent at 45 degrees, then the crescent phase illumination will switch to the opposite side at phase angle 315 degrees or vice versa. Mathematically, we are simply subtracting the current phase angle from 360 degrees to obtain the mirror phase angle.
[Invert Illumination] button simply toggles between illumination and shadow or light and dark. The illuminated part becomes the shaded part and vice versa. Mathematically, we are simply adding 180 degrees to the current phase angle to obtain the inverse illumination phase angle.
[Set to Random Phase] button does exactly what it implies and selects a random phase image to display each time the button is clicked.
[Set to Current Phase] button will compute and display the current phase of the moon (sans librations), as viewed from above the selected hemisphere, based on the NASA/JPL DE405 ephemeris model and the current UT.