Phase Day, the day of your personal phase return

Phase Day and phase return - what they are

Each of us has his or her own personal phase of the Moon - the phase that was in the sky at the moment of our birth.

There are four well known phases - New Moon, First Quarter, Full Moon and Last Quarter - and many people are born close to these phases, but in general the phase of the Moon is simply an angle between the positions of the Sun and the Moon from the terrestrial observer's point of view. Say, New Moon takes place when the Sun and the Moon are together in the sky, the angle between them is 0 degrees. At the first quarter, they are at the right angle and the Moon is 90 degrees ahead of the Sun. At the Full Moon, the angle is 180 degrees and at the Last Quarter the Moon is 270 degrees ahead of the Sun, another right angle.

But for most people, the degree between the Moon and the Sun at the moment of their birth will be a number like 23, or 151.3, or 211.123, or 347.654321... So that will be their personal lunar phase.

Consider an example. When Barack Obama was born, the Moon's position was 3.21 Gemini and the Sun's - 12.33 Leo (here and further on, notation like 3.21 will mean "three degrees and 21 minutes"). Converting zodiacal positions into ecliptical longitude, we shall have 63.21 for the Moon and 132.33 for the Sun. When calculating the phase, we are always interested to know how much the Moon is ahead of the Sun, so we subtract the Sun's position from the Moon's position. If the result is negative, we just add 360 degrees. Let's do the math:

63.21 - 132.33 = -70.48

-70.48 + 360 = 289.12

So Barack Obama's phase is 289.12. If you know where the Sun and the Moon were at the moment of your birth, you can find your own phase easily.

The idea is that whenever in the sky the Moon happens to be 289 degrees and 12 minutes ahead of the Sun (which happens every month), that will be a somewhat special time for Barack Obama. Similarly, whenever the angle between the Sun and the Moon in the sky will be equal to the angle at your birth, that will be a moment somewhat special for you.

Technically, the event when the phase in the sky repeats the phase at birth is termed phase return. A phase return happens at a specific moment in time, but its influence covers a longer period. For practical purposes, it will make to consider a period of 48 hours: 24 hours before the phase return and 24 hours after it. Let's give this period a special name: Phase Day.

To recap, Phase Day is a period of 48 hours, in the middle of which the phase return takes place. A Phase Day happens every month. Different people have different Phase Days as they depend on the exact moment of their birth.

You don't need to be an expert in math and astronomy to calculate your, or someone else's phase returns as we have created a special program named Phase Day exactly for that purpose. Currently, it is available for iPhone and iPod touch but will be soon ported to the other major mobile platforms.

Now, let's see why exactly our Phase Day is important for each of us.

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