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3/17/05 First Quarter Moon

Winner! This image took second place in the 2005 SCT-Users Group Imaging Contest - Best CCD Image of a Solar System Object category! The contest home page can be seen at

On this night the Moon was about as high in the sky as it can get. This happens occasionally and is caused by the tilt of Earth's axis and the tilt of the Moon's orbit around Earth. The Earth's tilt makes the the apparent path of the Sun, known as the Eliptic, move as much as 23.4 north and south of the celestial equator in our sky. This effect causes Winter and Summer in opposite hemisphere's on Earth as the Sun rides high or low in the sky. In addition, the Moon's orbit around Earth is inclined by about 5. The orientation of this tip wheels all around the ecliptic during the course of an 18.6 year cycle. This phenomenon is known as the regression of the nodes. During part of the 18.6-year cycle, the two tilts are oriented opposite each other and cancel each other out; but at other times during the cycle, the two tilts are oriented the same way and add together; causing the Moon to appear very high in the sky, as it did on 3/17/05. I took advantage of the effect and got this shot made of three sub exposures through the HA filter.