Heliacal Cycle

In a sidereal (stellar) zodiac, its all about the stars. As the Sun moves through the zodiac each star will disappear into the Sun for some time to reappear after the Sun has moved forward. The stars have a heliacal cycle; their cycle of being seen based upon the Sun's movement... which is our movement around the Sun. Here I use a generic 'star' to explain the cycle, but this movement will be the case for all stars and constellations.

The cycles begins with a star rising after it has not been visible for some time by its conjunction with the Sun. This is called it Heliacal Rise (udaya). It is associated with rebirth. Each day, the star stays longer and longer in the sky.

Then after the Sun has moved 90 degrees away from the Star, which takes approximately 3 months, it is seen in the meridian at the time just before sunrise.

Each day, the star continues to set later and later remaining in the night sky longer and longer.

As the Sun moves forward one degree a day, the star  gets farther from the Sun, till it becomes opposite the Sun. This takes approximately 6 months. At this time the star sets when the Sun rises... this means that the star rises when the Sun Sets.

This opposition of a star or a planet from the Sun is called the Acronychal Rise. Here a star will be visible for the entire night. It is considered the peak of strength for the star, its prime point of adulthood.

At this point the Sun is no longer moving away from the star. It has crossed the mid distance and is now moving towards the star. The star remains in the night sky less and less. At the beginning of the last quarter, the star is visible on the meridian after sunset.
rise.

Then the Sun approaches the star. There is a point when the Sun gets so close that the star is no longer visible. The last evening of visibility is the 'death' of the star, or the combustion of a planet. For a time the star or planet remains invisible until it returns to the sky in its heliacal rise.

The exact distance the star disappears into the Sun, or planet becomes combust the Sun, varies depending on the brightness (magnitude) of the star or planet. From the vantage point of the star gazer, it will also depend on the atmospheric conditions.

Below is a circular diagram which graphs all these cycles as an angle from the Sun (Heli), which is therefore the Heliacal Cycle.

The star Sirius is the brightest star in the sky (brighter than Saturn, Mars, and Mercury) and is therefore the most watched helical cycle.