Along the Ecliptic
At 5 p.m. CDT (22 UT) on the 18th, today, the sun in its apparent eastward motion along the ecliptic crosses the boundary between the constellations Pisces the Fishes
and Aries the Ram
as it enters the area of the sky containing the stars of Aries. This graphic shows the real position of the Sun on this date.
The banner graphic at the top of this page shows a larger view of the area including the point, Vernal Equinox, where historically it was used to mark the starting point for the change of seasons from northern hemisphere winter to spring. This celestial position is referred to as the ‘First Point of Aries
‘ even though the Sun is no longer at that position at the start of spring around March 20th. The shift of approximately one month is a result of a long term motion known as precession, or precession of the axis.
Precession is a wobble like motion the Earth has caused by the gravitational pull of the Sun and to a lesser extent, the Moon. The Earth leans at an angle of 23.5 degrees and over time, about 26,000 years the Earth wobbles and the poles of the Earth trace out a circle where any star on or near the precession circle will be the pole star.
Another effect of precession, as the Earth wobbles, is that the celestial coordinate system, which is based on the Earth’s geographical coordinate system (latitude and longitude) moves or shifts toward the east with respect to the stars and constellations. The stars in the background stay fixed, more or less, in their location, while the celestial coordinates move as the Earth is precessing. The result is that several centuries ago the sun was in Aries at the start of spring, now the Sun is further west across Aries and has nearly precessed into Pisces.
Click here to go to the Qué tal in the Current Skies web site for more observing information.