You could use the following options:
1. Using the English spelling:
* แคสซิโอเปีย (Kae-ssi-o-pi-ya) - This is a phonetic spelling of the English word, pronounced as closely as possible in Thai.
2. Using the scientific name:
* แคสซิโอเปียเอ (Kae-ssi-o-pi-ya A) - This uses the scientific name of the constellation, "Cassiopeia A," and is more specific.
3. Using the Thai name for the constellation:
* There is no specific Thai name for the constellation Cassiopeia, but you could refer to it as กลุ่มดาวแคสซิโอเปีย (Klum Dao Kae-ssi-o-pi-ya), which means "Cassiopeia constellation."
Ultimately, the best option for you will depend on the context and your desired level of formality.