What are optical doubles?
Optical doubles are two stars that seem close together because they happen to lie in almost exactly the same direction as seen from earth. Optical doubles are not binaries and the stars are not linked in any way.
What is meant by the precession of the Earth?
The Earth actually spins about a wobbling axis and the movement of the wobbling axis is known as precession of Earth.
What is the precession or precessional translation of the Poles?
The Earth’s axis turns very slowly during the precession of the Earth’s axis, and describes a full circle once in 25,800 years. The circular movement of the Earth’s poles due to this precession is called the precessional translation of the Earth’s poles.
What is the effect of the precession of the celestial poles on the Zodiac?
Precessional translation of the poles results in a shift of not only the celestial poles but also the celestial equator relative to the ecliptic. Hence when the pole shifts, the vernal equinox also shifts along the ecliptic, completing a full cycle every 25,800 years. When the ancient astrologers defined the Zodiac during the second century B.C., the vernal equinox occurred while the Sun was in the constellation Aries. They were, however, unaware of the precessional translation of the celestial poles and made no corrections for it in their calculations. Subsequently the point of vernal equinox has moved from Aries to Pisces due to precessional effect. Naturally, all the other zodiacal signs are also one constellation behind relative to their original position. However, astrologers regard 21 March, the day vernal equinox to lie in Aries even today. It is also called by them as the ‘First Point of Aries’ since it is the point of vernal equinox or the beginning of the year for them when they consider the Sun to enter the sign of Aries.
Do the constellations undergo a change in shape?
Yes. Over a very long period, due to the movements of the stars in different directions, the constellations slowly change shape.
What is the best possible time for viewing the planets in the night sky?
Mercury and Venus are best viewed in the hours just before sunrise and just after sunset. The other planets appear with full intensity when situated due south.