Need help reconciling star risings

[AncientHistorian]

Hello, I am trying to figure out how heliacal risings and settings work. For example, here is a passage from a book written in 1908 by a professor in Edinburgh, Scotland:

But I with break of day will turn my oxen on to the land and sow the fields ') is defined as taking place at the setting of the Pleiades, i. e. the cosmical setting of the Pleiades twenty-five days after the autumnal equinox. The harvest is to take place at the rising (heliacal) of the Pleiades, i. e. twenty-seven days after the vernal equinox. Hesiod then adds the remark that the Pleiades are invisible (KeKpixfxrrm) for forty days and forty nights, i. e. owing to their proximity to the sun they are invisible, though really above the horizon, for a certain period before conjunction and for a certain period after conjunction, but 'shine again with the revolving year, when first the sickle is sharpened ', i. e. they now arrive sufficiently in front of the sun to be visible on the eastern horizon just before sunrise, i. e. they now rise heliacally. It should be observed that at the present day the Pleiades are invisible in this country for more than sixty days, from the end of April to the beginning of July, being in conjunction about May 18.

I have the software Alcyone Visibility (PLSV). I set it to the star Alcyone, one of the Pleiades, than entered an observation place of Edinburgh, Scotland. I set the year to 1908. The software then gave me the following information: heliacal / acronychal dates for Alcyone in 1908 location : Edinburgh, Scotland (UK) latitude : 55° 57' 00'' N longitude: 3° 10' 12'' W arcus visionis: heliacal: arcvis = 14.52° acr/cos : arcvis = 12.06° critical altitude: 0.00° date obj r/s sun r/s d r/s age mag last visibility 1908-04-30 22:08 19:49 2:19h -19d 06h 2.9 acronychal rising 1908-08-12 21:42 19:57 1:45h -100d 12h 2.9 cosmical setting 1908-12-17 07:00 08:39 -1:38h 25d 21h 2.9 This does not seem to match the authors statement that the "the Pleiades are invisible in this country for more than sixty days". How can understand this? Thanks for any assistance? Also, is this a "beginner" question or does it belong in a different topic?

[AncientHistorian]

I attached a screen shot. Here is the data:

[pre]

heliacal / acronychal dates for Alcyone in 1908

location : Edinburgh, Scotland (UK)

latitude : 55° 57' 00'' N

longitude: 3° 10' 12'' W

arcus visionis:

heliacal: arcvis = 14.52°

acr/cos : arcvis = 12.06°

critical altitude: 0.00°

date obj r/s sun r/s d r/s age mag

last visibility 1908-04-30 22:08 19:49 2:19h -19d 06h 2.9

acronychal rising 1908-08-12 21:42 19:57 1:45h -100d 12h 2.9

cosmical setting 1908-12-17 07:00 08:39 -1:38h 25d 21h 2.9

[/pre]

[Tim]

There is a free program called Stellarium you can download. Just input your desired location and date and see a graphical representation of the position.

I find that helps me visualise the data more effectively.

By the way, what difference does it make? Or are you just verifying the statements?

Cheers

Tim

[AncientHistorian]

I am trying to understand why the statement in the book does not seem to be reflected by the Alcyone results.

My overall goal is to be able to figure out ephemerises competently. The passage in the book is just one of bunch of similar statements I want to verify and understand.

[acey]

I don't understand why the author should have thought to mention the visibility of the Pleiades in Scotland, given that he is referring to Hesiod (who in turn, I'm guessing, may be referring to observations in Egypt).

Nor do I know how heliacal rising is defined for the purposes of computer programs, given that it refers to the visibility of the object to the human eye in the pre-dawn sky, not the actual rising of the object above the horizon. A very keen observer in Hesiod's time might have been able to see the Pleiades on a morning when others couldn't.

Of more relevance, then, is to determine the method used by Hesiod's sources to define the date of heliacal rising, then compare this with data drawn using the same method from the author's location at the appropriate date.

Who was the anonymous professor? Does he give a reference? Maybe he made a mistake.