<P> Also, unlike most other solar measurements, sunrise occurs when the Sun's upper limb, rather than its center, appears to cross the horizon . The apparent radius of the Sun at the horizon is 16 arcminutes . </P> <P> These two angles combine to define sunrise to occur when the Sun's center is 50 arcminutes below the horizon, or 90.83 ° from the zenith . </P> <P> The timing of sunrise varies throughout the year and is also affected by the viewer's longitude and latitude, altitude, and time zone . These changes are driven by the axial tilt of Earth, daily rotation of the Earth, the planet's movement in its annual elliptical orbit around the Sun, and the Earth and Moon's paired revolutions around each other . The analemma can be used to make approximate predictions of the time of sunrise . </P> <P> In late winter and spring, sunrise as seen from temperate latitudes occurs earlier each day, reaching its earliest time near the summer solstice; although the exact date varies by latitude . After this point, the time of sunrise gets later each day, reaching its latest sometime around the winter solstice . The offset between the dates of the solstice and the earliest or latest sunrise time is caused by the eccentricity of Earth's orbit and the tilt of its axis, and is described by the analemma, which can be used to predict the dates . </P>

The first part of daybreak pierced the sky