* It's a variable star: TZ Orionis's brightness changes over time, making it difficult to determine when it was first noticed as a separate object.

* Early astronomy: Before telescopes, many stars were simply cataloged as "stars" without individual names or designations.

However, we can say this:

* TZ Orionis was likely known before 1900: The earliest known observation of TZ Orionis's variability was in 1900 by the astronomer E.C. Pickering using photographic plates. This suggests the star was likely known before that, possibly by visual observation.

* Modern catalogues: TZ Orionis is now recognized as a variable star and appears in modern star catalogues, such as the General Catalogue of Variable Stars (GCVS).

Therefore, while we don't have a specific date of discovery, it's reasonable to assume TZ Orionis was likely known as a star long before 1900, and its variability was first noted in 1900.