Tau4 Serpentis
star in the constellation Serpens
Tau4 Serpentis, Latinized from τ4 Serpentis, is a variable M-type giant star in the constellation of Serpens, approximately 710 light-years from the Earth. Its brightness varies from magnitude 5.89 to 7.07, making it occasionally bright enough to be faintly visible to the naked eye under very good observing conditions.
With a spectral classification M5IIIa, Tau4 Serpentis is a cool red giant star. The spectrum varies, and some sources classify it between M4IIIe and M6IIIe. Some of its spectral lines show an inverse P Cygni profile, where cold infalling gas on to the star creates redshifted hydrogen absorption lines next to the normal emission lines. Sometime between the years 1868 and 1877, John Ellard Gore discovered that the star's brightness varies. It is classified as a semiregular late-type variable, and its magnitude varies between +5.89 and +7.07 with a period of approximately 100 days.
τ4 is unique among the stars with the Bayer designation τ Serpentis as being the only one with no HR catalog number.
The public source identifies “Tau4 Serpentis” as star in the constellation Serpens. This brief keeps that definition visible, then builds a research path around Tau4, Serpentis and star.
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The citation trail is more important than the brevity of the summary: it shows where individual claims can be examined in context. The source revision retrieved here is dated May 20, 2026. The linked authority identifier is Q5178125. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1868 and 1877.
Overview language is designed for orientation and should not be treated as a substitute for the evidence cited beneath it. The source lead contains qualifying language; that uncertainty should survive quotation, summary and reuse. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
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This entry incorporates text from “Tau4 Serpentis” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.