new moon
The term new moon ( Latin interlunium ), in Switzerland also empty moon (which is actually the more appropriate term for an invisible, even "empty", moon), describes the light shape ( moon phase ) of the moon that is invisible to the naked eye ( moon phase ) when this is located between earth and sun , that is, in conjunction with the sun. During this constellation you can only see the night side of the moon from Earth . Only after about 35 hours is the extreme right edge (left edge, if observed from the southern hemisphere) illuminated again by direct sunlight. This moon phase is the new light . The phase before is called the new moon , because the moon seems to "renew" itself in it. The last visible phase before the new moon is called old light . The second new moon in a month and the third new moon in a season with four new moons is known as the black moon .
The side of the moon facing the earth always receives some sunlight reflected from the earth ( earth shine ), but when the moon is new it is outshone by the sunlight scattered in the earth's atmosphere , so that the moon cannot be seen with the naked eye. In principle, the new moon cannot be seen in the night sky because it is below the horizon together with the sun.
A more precise, temporal definition is:
"New moon is the point in time when the geocentric ecliptical longitude of the moon and the geocentric ecliptical longitude of the sun are equal."
Here is geocentric : from a hypothetical observer in the center of the Earth seen. The definition is therefore independent of the location of a real observer; New moon occurs worldwide at the same time (which however corresponds to different local times in different time zones).
The period between two new moons is on average 29.53 days and thus significantly longer than one orbit of the moon around the earth, which takes 27.3 days. This is because the earth and moon move together around the sun, which changes the position of the sun against the starry background. When the moon has completed one orbit around the earth, the sun is already in front of another point on the star background. Since the new moon only occurs as soon as the moon is back on the ecliptical longitude of the sun, the moon must move around the earth accordingly until the next new moon. (Compare: Synodic Period and Sidereal Period )
The astronomical symbol for new moon is a filled circle:
Special effects of the new moon
Solar eclipse
After about every sixth lunation , the moon has almost zero for its ecliptical latitude while apparently overtaking the sun . In these cases it passes the nodal line (intersection between the plane of the lunar orbit and the ecliptic plane ) at moments when this approximately coincides with the connecting line between the centers of the earth and the sun. This applies to both the new moon and the full moon . With a new moon there is a solar eclipse , with a full moon a lunar eclipse .
Spring tide
A spring tide takes place both at a new moon and at a full moon. Tidal forces from the sun are added to the tidal forces acting on the earth (mainly attraction on the side facing the moon, mainly centrifugal forces), which come mainly from the moon (or from the circular movement of both around the common center of gravity) , both when the moon is in Conjunction as well as in opposition to the sun. In such cases the tide is higher than average. If the moon and the sun form a right angle (increasing and decreasing crescent moon ) when viewed from the earth , the tide is the smallest and is called nipptide .
Web links
- Moon Watch (HMNAO) (English)
- NASA Eclipse Web Site ( Memento from March 20, 2008 in the Internet Archive ) - moon phases from −2000 to 4000.