First Author of a Research Publication/ Journal [duplicate]

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• What does first authorship really mean? 15 answers

This may come as a basic question but can I get a general feel of what most people in the research community think of the contributions made towards fulfilling a 'first author' of a research publication? Now, my general understanding of a first author may be considered naive by some but here goes: [1] Did most (or all, which is quite difficult in this day and age) of the work to answer the research topic of interest [2] Wrote most (or all) of the content of the article, basically the one who made the most significant contribution towards the article.

Is that a too narrow scope or are there many in-between/ grey areas to consider?

Reason for me asking is that I've observed a number of senior researchers in various labs basically being the orchestrator of the project by getting multiple students/ research assistants/ lab technicians do ALL the experiments while the the senior gathers all the data and writes the bulk of the article and presents him/herself as the first author. Is that an acceptable practice? Based on my personal criteria listed above, the senior would fulfill half the criteria as a first author... As such may I ask around what is the opinion of others to see if my personal criteria needs some re-thinking...