Sphere
Sphere
Cueball: How are you? Megan: Trapped on the surface of a sphere. [A beat.] Cueball: That astronomy class has made you suck at small talk. Megan: The universe is too big for small talk.

Megan has taken or visited an astronomy class and has become more conscious and aware about the colossal size of the universe, and our own minuscule place in it. She ponders that she can only observe and learn about the rest of the universe; she cannot explore it directly as she is trapped, probably by the constraints of our gravity well, time and human technology.
The sphere she mentions here is the Earth , whose surface is roughly spherical in shape. The figure of the Earth is an irregular shape which can be better approximated as an oblate spheroid , or more specifically as a geoid .
Her disinclination to make " small talk " with Cueball is a reference to how astronomers and people of other 'big-science' specializations can be so focused on their topic that they become disconnected from the simple details of everyday life. This has also been touched upon in 663: Sagan-Man and 786: Exoplanets .
The concept of "small talk", which is usually used as a colloquial term meaning insignificant chatter with others, is taken quite literally by Megan to be small in size. The word itself is juxtaposed with the size of the universe shortly after, which also ties into her previous sentence of being trapped on a "sphere". It seems that astronomy, which deals with ideas of a vastly large scale, has expanded Megan's views to the point where she feels insignificant herself, as well as other matters that concern her. Her gaze outwards also reinforces this suggestion, especially during her conversation with Cueball. She does not engage in eye-to-eye contact, instead replying without looking directly at him. This implies that she is disregarding the current conversation as insignificant as well, which furthers the assumption of Megan's expanded scope of viewpoint.
The title text is a continuation of this theme. The name "Society of Astronomers Trapped on the Surface of a Sphere" or, "SATSS", follows a common naming practice for scientific communities, Society, or Association, or Union of <Scientists> of <Country, Nationality, or What Ever>.
Cueball: How are you? Megan: Trapped on the surface of a sphere. [A beat.] Cueball: That astronomy class has made you suck at small talk. Megan: The universe is too big for small talk.
