Moon's
revolution around the Earth takes 27.3 days; however, because the
Earth has moved during this period,
the phase cycle takes 29.5 days.
The period of the lunar phases (synodic period) is slightly more than 2 days longer than the
moon's orbital period (sidereal period).
Phases of the Moon: first quarter looks like a letter "P"
Eclipses
Solar and Lunar Eclipses
Total Solar eclipse happens when the Moon is close enough to the Earth, so tha the
dark part of the Moon's shadow (the "umbra") reaches out to the Earth.
"Annular" Solar eclipse happens when the Moon is not close enough to the Earth, so that
only the dimmer part of the Moon's shadow (the "penumbra") reaches out to the Earth.
In this case only a prt of the Sun's disk is covered, leaving a bright ring ("annulus").
The dark part of the Moon's shadow covers only a small part of the Earth. As a result
solar eclipses are not often visible.
Lunar eclipses happen when the Moon passes through the Earth's shadow, thus
near Full Moon. However, this does NOT happen once a month since the Moon's
orbit is tilted by 5 degrees so the shadow can pass above or below the Moon.
During a Lunar eclipse the Moon has a reddish glow. This is due to the light that is reflected
from the Earth to the Moon and then back to the Earth.
Time Zones and Calendars
The Sun is the highest up in the sky at Solar Noon, which depends on the Longitude, hence Time Zones.
The Time Zones have been adjusted for geographic convenience.
A year has 365 and 1/4 days. The Julian Calendar (Julius Caesar, 46 BC) introduced "leap years"
to correct for the 1/4 extra day. Named July in his honor. The month of August in honor of another
emperor, Octavian Augustus; he took a day from february and added it to his own month - the August.
Julian calendar had a year still a few minutes too long. Pope Gregory dropped 10 days to compensate
in 1582. he introduced the Gregorian Calendar has leap years every four years, except for those
that can be devided by 400 (e.g. year 1600 is not a leap year).
This page was created on September 10, 2003 by V. Dobrosavljevic.
the phase cycle takes 29.5 days.
The period of the lunar phases (synodic period) is slightly more than 2 days longer than the
moon's orbital period (sidereal period).
Phases of the Moon: first quarter looks like a letter "P"
Eclipses
Solar and Lunar Eclipses
Total Solar eclipse happens when the Moon is close enough to the Earth, so tha the
dark part of the Moon's shadow (the "umbra") reaches out to the Earth.
"Annular" Solar eclipse happens when the Moon is not close enough to the Earth, so that
only the dimmer part of the Moon's shadow (the "penumbra") reaches out to the Earth.
In this case only a prt of the Sun's disk is covered, leaving a bright ring ("annulus").
The dark part of the Moon's shadow covers only a small part of the Earth. As a result
solar eclipses are not often visible.
Lunar eclipses happen when the Moon passes through the Earth's shadow, thus
near Full Moon. However, this does NOT happen once a month since the Moon's
orbit is tilted by 5 degrees so the shadow can pass above or below the Moon.
During a Lunar eclipse the Moon has a reddish glow. This is due to the light that is reflected
from the Earth to the Moon and then back to the Earth.
Time Zones and Calendars
The Sun is the highest up in the sky at Solar Noon, which depends on the Longitude, hence Time Zones.
The Time Zones have been adjusted for geographic convenience.
A year has 365 and 1/4 days. The Julian Calendar (Julius Caesar, 46 BC) introduced "leap years"
to correct for the 1/4 extra day. Named July in his honor. The month of August in honor of another
emperor, Octavian Augustus; he took a day from february and added it to his own month - the August.
Julian calendar had a year still a few minutes too long. Pope Gregory dropped 10 days to compensate
in 1582. he introduced the Gregorian Calendar has leap years every four years, except for those
that can be devided by 400 (e.g. year 1600 is not a leap year).
This page was created on September 10, 2003 by V. Dobrosavljevic.