Solar System to scale

NOTES: The Earth-Moon SystemThe parallax of a feature on the moon over a night gave Ptolemy the distance to the moon in earth diameters (diagram on board).The following formula was then used to find to find the diameter of the moon. It can be used to find the diameter of any object.Diameter = Distance x Angular Diameter (in radians, 1 radian = 57.3o)

The moon's orbit is not perfectly circular (overlay).Tidal force of the moon made the earth an oblate spheroid.Spring tides have a higher high tide caused by the alignment ofearth, moon, and sun.Neap tides have a lower high tide, as the sun is at right angles to the moon's position.Eclipses:

For either lunar or solar, the moon's orbit (tilted by 6o) must cross ecliptic plane at one of two positions called lunar nodes.

In addition, for a lunar eclipse, the sun and moon are in opposition (full moon). For a solar eclipse, the moon is between the earth and sun (new moon).

A lunar eclipse is the same everywhere on earth. A solar eclipse is total only on a 50 mile-wide swath across the earth. Thus lunar eclipses are more frequent in a given location than solar. (See overlay).

A lunar eclipse always involves the whole moon but may be gray instead of totally dark. This is a penumbral eclipse.

A solar eclipse is annular when moon is closer to earth.Total solar eclipse returns every 18.6 yrs (Saros cycle).

The parallax of a feature on the moon over a night gave Ptolemy the distance to the moon in earth diameters

The following formula was then used to find to find the diameter of the moon. It can be used to find the diameter of any object.Diameter = Distance x Angular Diameter (in radians, 1 radian = 57.3o)

The moon's orbit is not perfectly circular. It is 42,000 km different in distance from perigee to apogee.

Perigee

Apogee

Tidal force of the moon made the earth an oblate spheroid.Spring tides have a higher high tide caused by the alignment Of earth, moon, and sun.Neap tides have a lower high tide, as the sun is at right angles to the moon's position.

Moon’s orbit is tilted and crosses ecliptic at lunar nodes.Moon must be near those points for solar OR lunar eclipse to occur.

Lunar eclipse varies with the region of shadow:Total—in umbraPartial—part in umbra and part in penumbraPenumbral—in penumbra only.

Total Lunar Eclipse: the red appearance is caused by red light refracted around the earth.

50 mi wide path of total shadow Total eclipse

Annular (‘ring’) eclipse of sun:Occurs when the moon is farthest--near apogee.

Diamond Ring effect—solar eclipse

Eclipse path patterns: repeat in Saros cycle.

Hackpen Hill, near Broad Hinton, Wiltshire. Reported 4th July 1999

Crop Circle!