Cusps appear to be somewhat misunderstood in astrology, or at least subject to debate. A “back to the basics” type examination of cusps may not completely settle differences of opinion regarding cusps, but suggests a cogent (and in my view, correct) manner of thinking about them.
Simply stated, the definition of the cusp between two signs is the exact beginning of a zodiac sign (e.g., 0' 00” Aries, 0' 00” Gemini, 0' 00” Scorpio, and so on). Houses also have cusps, defined by the house system and apparent through generating a horoscope. The zodiac has twelve signs and therefore twelve cusps; likewise, an astrology chart also has twelve house cusps.
I hesitate to use the 'confusion' buzzword, but it is most appropriate when any question of cusps is raised on social media. Does a Virgo Sun at 28' 15” Virgo have Libra characteristics? Does a Capricorn Sun at 1' 22” Capricorn have Sagittarius features? Exactly how close must a planet be to a cusp, to be influenced by the previous or next sign or house?
One way to resolve the cusp issue is to look at the definition of how a planet manifests: via its sign. Notice how this by and large negates doubt about how close a planet must be to a cusp in order to take on characteristics of the sign it isn't residing in. With the exception of the Sun and Moon, and only in a small fraction of cases will Sun and Moon be exceptions, a cusp is not a factor in how a planet manifests. If Mars is at 29' 59” Libra, he is in his detriment: brash, headstrong, fiery Mars must adjust to the elegant, balancing, and intellectual Libra sign. If Mars is at 0' 00” Scorpio, his overlord's (Pluto's) sign, he is in classical dignity: intense, powerful, vengeful, and perceptive and intuitive. Mars may similarly be close to a Midheaven angle, but either in the ninth house or the tenth ‐ how can he be in both? He either resides in the more philosophical and expansive area of life, or the more career‐oriented and public area of life. Mars close to the Midheaven is an interesting case and arguably makes him more important in the chart, but he is still in either house ‐ not both.
Of interest, we observe the Sun or Moon from earth as disks about 30 minutes of arc length wide. All other planets are dots of light, and in the case of planets beyond Saturn, unable to be seen without a telescope. The problem with Sun and Moon on the cusp ‐ very close to 0 Aries, for example ‐ is that part of either planet's disk may be in one sign (in this example, Pisces) at the same time part of the disk is in the next sign (Aries). Recall how a planet manifests ‐ via its sign! Thus Sun or Moon at 0' 00” Aries is half in Pisces, half in Aries, and consciousness/the basic identity (Sun) takes on qualities of both signs. Examples are in order.
Vanna White, February 18, 1957, 2:35 PM, Conway, SC, USA (Source: Astrotheme)
Vanna White has Sun at 29' 54” Aquarius, based on an exact birth time. Is she an Aquarius Sun? Part of the Sun's disk is in Pisces! Sun's disk is about half a degree of arc in the sky, creating a problem when determining Sun's sign in the case of Vanna White. While over half of Sun's disk is in tropical Aquarius in her natal promise, a significant portion is in Pisces. Uranus and Neptune both rule her Sun. The core of her personality must take on characteristics of both Aquarius and Pisces ‐ if this is not so, the definition of Sun manifesting in the personality via the natal promise must be redefined. In Vanna White's case, her Sun is a lead player in her career choice. She is a household name, based on her celebrity status as appearing on a widely watched television game show. White is both friendly and sporadic (Aquarius) and has charmed and entertained a mass audience for several decades on television (Pisces).
Moon may also certainly be on what I like to refer to as the “true cusp” of a sign ‐ part of the disk in one sign and partly in the next sign. Mel Gibson, born about a year before Vanna White, has a natal promise containing Moon on the true cusp of Virgo and Libra.
Mel Gibson, January 3, 1956, 4:45 PM, Peekskill, NY, USA. (Source: Kepler 7.0)
Moon is at 0' 01” Libra, and therefore almost half of Moon's disk at the time of Gibson's birth is in Virgo. The emotional base is an amalgamation of the need to be meticulous and analytical (Virgo), and also the need to be balancing, harmony seeking, and collaborative (Libra). Mel Gibson's celebrity status and success has undoubtedly drawn on the strengths of his Moon placement. Regardless, both Mercury and Venus rule Gibson's Moon, and Moon's placement is divided between tropical Virgo and Libra. Note also several planets in late degrees, with Saturn and Mercury in the anaretic degrees of their signs ‐ but not on the cusps! Saturn and Mercury are still in Scorpio and Capricorn, respectively.
The talk of Sun and Moon about half a degree of arc as observed from earth raises the issue of the other eight planets on the cusp. Venus, similar in size to earth and relatively close, is not measured in the sky as observed from earth in arc minutes but in arc seconds. Thus any talk of Venus or other planets on the true cusp of two signs involves knowing an exact birth time and moreover, manifesting at the exact time of transiting exactly zero degrees of a sign. Venus on a true cusp would be fascinating, but very difficult to find. A person would have to be born just as Venus hits 0' 00” of any sign. This creates possible difficulties ‐ noise in astrology software may render finding the exact time to be difficult and unreliable (would Solar Fire and Kepler show slightly different times for Venus at exactly 0 Aries, for example?). Another problem is that birth certificate time may differ from a rectified time. Moreover, Venus is the best case for a planet besides Sun or Moon being on a cusp. Mercury and Mars are both visible, but both planets are smaller and less arcseconds wide than Venus. Jupiter is a huge planet, but very far away from earth. Neptune is not visible from earth without a telescope and quite distant from earth. Steve Harris (Iron Maiden) was born on a day when Neptune moved from Libra to Scorpio, elucidating the problem of finding a planet on the cusp.
Steve Harris, March 12, 1956, unknown birth time (Noon used), Essex, England. (Source: Astrotheme)
Neptune changed signs at about 11:55 AM England time on the day Harris was born. Note that Harris must have both Sun and Moon in Pisces in his natal promise, although phase (and indeed, even Moon phase is subject to the same issue! The disk can be in both the New and Balsamic phase in theory) depends on Harris' time of birth. Neptune is a key planet in Harris' chart. Neptune rules the luminaries and was very close to either changing signs or had just changed signs, when he was born. Very precise calculations would have to be made to determine when Neptune was on the true cusp of Libra and Scorpio. In turn, whether Harris has Neptune on the true cusp of the two signs depends on an exact birth time, which we don't know. Neptune is typically prominent in composers' charts. Harris has Neptune ruling Mercury (communication) and the luminaries, which probably explains much of his musical ability. Perhaps Neptune rules his chart as well, per a Pisces ascendant. His natal promise would be an interesting rectification project, in addition to the example of Neptune close to 0 Scorpio.
Basically, planets besides Sun and Moon cannot be reliably used as planets “on the cusp” and need to be treated as manifesting via their apparent sign. Sun or Moon between 29' 45” and 0' 15” of their signs must be treated as on the cusp, per the definition of how a planet manifests (via its sign).
Your own experience of your natal promise, and practice of astrology, is most reliable in making observations about a concept such as a planet on the cusp. However, I encourage you to consider my definition. And please provide the link to my article when someone yet again asks about planets on the cusp!
