Conjunction. The conjunction is a zero
degree aspect, meaning that two planets are close to each other.
The conjunction can be positive or negative, depending upon the planets
involved.
Semi-sextile. The semi-sextile is a
minor aspect that not all astrologers use often. It is a 30-degree
aspect which tends to indicate minor tension between the two bodies involved.
Semi-square. The semi-square is a 45-degree
aspect that tends to bring about stronger tension between the two points
it affects.
Sextile. The sextile is considered an
easy, flowing aspect. It is a 60-degree aspect.
Square. The square is a 90-degree aspect
that indicates considerable tension between the two parts of the chart
involved. The tension is usually more of an inner nature, rather
than tension coming from outside forces.
Trine. The trine is usually considered
the most beneficial aspect between planets. It is a 120-degree aspect,
and indicates ease, flow, and innate gifts.
Quincunx. The quincunx is another minor
aspect not always used by astrologers, although I favor using it, even
with an 8-degree orb (see below). Like the semi-square, it invokes
tension, but it is a tension born more from outside forces and can even
be karmic in nature. Its mathematical relationship is 150 degrees.
Opposition. The opposition is the 180-degree
aspect, with two planets on opposite sides of the chart wheel. It
is also an aspect of tension, but the tension often comes from outside
sources when this aspect is present.
Other aspects do exist, including the quintile and biquintile, often considered as "innate gift" aspects. My personal preference is to use only the aspects listed above.
Astrologers do not agree on the questions of orbs, either. An orb is how many degrees before and after an exact aspect to allow. For instance, the sample chart has a trine aspect between Venus and Saturn which is slightly over eight degrees. I would still read this as a trine aspect, although most astrologers use eight degrees or less as an orb with the "major" aspects.
Common orbs are eight degrees (on either side of exact) allowed for the conjunction, square, trine and opposition (although some give 10 degrees for these aspects if they involve the Sun or the Moon); six degrees allowed for the sextile; and two degrees allowed for the minor aspects.
The aspect colors the nature
of the natal planets. For instance, the sample chart has the aforementioned
Venus trine Saturn aspect. With Venus in the 12th and Saturn in the
5th house, we might expect this person's romantic life to be lonely and
difficult. But the trine connecting the two planets allows for an
easier resolution of this dilemma than would be apparent if the chart instead
had Venus and Saturn in square aspect.