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Days of heliacal rising and setting of a star

Days of heliacal rising and setting of a star

Our sky is filled with thousands of stars visible with the naked eye. Some of them remain visible all year long. These are the stars which define the geometrical outlines of the northern circumpolar constellations like Ursae Minoris (the Small Dipper), Ursae Majoris (the Big Dipper), Draco, ... On the contrary, the southern circumpolar stars remain invisible to the european, the russian or the north-american observer. This is due to his (her) geocentric latitude. An australian or a south-american observer effectively enjoys a reversed situation : he (she) can see the Triangulum Australe and the Octans but not the Big Dipper nor the Draco, indeed. In the one and the other cases, most of the stars visible with the naked eye however fill an intermediate area, located between the northern and southern circumpolar areas, which the Sun yearly seems to travel. During its apparent yearly course, the Sun goes near then moves away from everyone of these stars. On their conjunction day, most of them are unseen with the naked eye. Several days, weeks, even months later, they make their heliacal rising, that is to say, their reappearance at dawn. Their heliacal rising puts an end to their yearly period of invisibility which began on their day of heliacal setting, that is to say, on the day they became unseen in the twilight sky.

Heliacal rising

At intermediate latitudes, most of the stars lie within the northern and southern circumpolar areas. Their daily and yearly periods of invisibility seem all the longer to the northern hemisphere's observer since the star lies far away from the northern circumpolar area.

The yearly period of invisibility of a star - that is to say, the time elapsed between its days of heliacal rising and setting - mainly depends upon its apparent magnitude, its distance from the ecliptic line, the latitude and the altitude of the site chosen for observation, meteorological parameters and the visual acuity of the observer. It is necessarily between 0 and 365 days. A star whose yearly period of invisibility is equal to 0 or 365 days is a circumpolar star ; it makes no heliacal setting nor any heliacal rising. Any other star sets and rises heliacally during the year.

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This software invites you to accurately determine the days and time of heliacal rising and setting of any star visible with the naked eye of the Hipparcos catalog (5043 stars in total) at any year between -4712 and 2025. To do so, it combines various astrometry (relative to the positioning of the stars in the sky) and photometry (relative to the brightness of the observed star and the conditions of local visibility) algorithms published within the scientific articles whose list appears below.

Free tests of this software are available within the Client Area. The access to the user interface of this software is made on payment : 20 euros, which can be paid via the Paypal secured paiement system (right button). This amount includes an unlimited access to the user interface and a free access to any future updates.

Price : 20,00 euros

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