Due to Llewelyn's interest in astronomy, her father constructed an equatorial observatory at Penllergare Valley Woods for her sixteenth birthday. The construction of the observatory was a family affair, as Llewelyn described the event in an 1851 letter to her father:
I laid the foundation stone of the observatory today, July 7th. When Grandpa and Grandmama were here on Saturday we told them about it and they were so very kind as to come over here today and to see the first stone laid; so we went in procession to the place; they had got some stone already and after I had laid the first stone Emma laid the second and Elinor the third, which she was very much delighted to do.
Llewelyn collaborated with her father in a number of astrophotographic experiments, including the production of some of the earliest photographs of the moon in the mid-1850s. She later recalled how "as moonlight requires much longer exposure, it was my business to keep the telescope moving steadily as there was no clockwork action." They also developed a means to photograph snow crystals. Collaboration between Llewelyn and her father also extended to meteorology, as they contributed to the maintenance and monitoring of the British Association's volunteer weather stations. Llewelyn managed the meteorological records and hoped to present her observations in person at a meeting of the Association. However, her father did not allow her to attend. One of John Dillwyn Llewelyn's photographs of his daughter, taken around 1854, has a photogram of ferns as a vignette border rather than the lace, ink and watercolour, or papercut borders that were common at the time. Llewelyn adopted this decorative method for at least one of her photographs of her sister, Elinor. In addition to photography, Llewelyn compiled a herbarium and wrote a report that was read at the Linnean Society in 1857. Llewelyn may have observed Donati's Comet in 1858 before it was officially announced by the Italian astronomer. Following her marriage to Maskelyne, the two collaborated on experiments in chemistry and photography. In 1874, Llewelyn corresponded with Charles Darwin in the pages of Nature about her observations of birds biting flowers to eat nectar.
Legacy and archives
In 2012, the British Library acquired the Dillwyn Llewelyn/Story Maskelyne photographic archive, which includes a selection of Thereza's journals, memoirs, and photographs.
