Baily’s Beads Study Window

The window displays a graph of the LRO lunar limb profile and the Sun in the background as seen from the observer’s current location at either second or third contact and maximum eclipse. It is then possible to change the time of the display to see how the Sun moves behind the Moon’s rugged terrain.

Choose Display > Baily’s Beads Analysis…

The Moon exhibits an irregular limb when seen in profile, due to its surface topography. Most eclipse calculations assume some mean radius that averages high mountain peaks and low valleys along the Moon’s rugged limb. Data from the Lunar Reconnaissance Orbiter probe is used for higher accuracy in those calculations.
The mauve limb is LRO. The brown dotted line charts the reduced mean lunar radius k₂, usually used to compute the uncorrected second and third contacts and the umbral or ant-umbral path. The blue dotted line is the mean radius used for the data of the LRO and Kaguya probes. The vertical axis unit is arc-seconds and the unit of the position angle of axis on the horizontal axis is degrees.
The positions of second and third contacts, corrected or not, are identified by the C2 and C3 symbols when uncorrected, C2' and C3' when corrected. The limb of the Sun is also displayed as a dotted curve in orange for second contact and in green for third contact. The position of the Sun is also indicated at the given instant which can be adjusted using the time slider.
A click anywhere on the graph will reveal the position angle of axis value and the height with reference to the IAU mean lunar radius (1738.091 kilometers or k = 0.2725076).

A contextual menu, that can be invoked with a right click, will let you select various options:

Axis Angle - Select the graph direction from either Increasing or Decreasing, the angles starting at the lunar north pole and counted to the east. Increasing by default.
Graph Size - Select the lunar height resolution. 14400 by 400 pixels by default.
Around Second Contact - Sets the time to the second contact and then updates the position of the Sun.
Around Maximum Eclipse - Sets the time to the maximum eclipse and then updates the position of the Sun.
Around Third Contact - Sets the time to the third contact and then updates the position of the Sun.
Save the Graph to a PNG File… - Lets you create a color high-resolution PNG image file containing the Baily’s beads study.
Export the Graph Data to a Text File… - Exports the lunar limb profile data for the current topocentric libration in a text file.

The Update Profile button allows to update the lunar limb profile.
A clic anywhere in the graph area will display in the lower left corner of the window the corresponding values of the position angle of axis in degrees and the limb height in arc-seconds.