On the evening of September 14, a Venus occultation occurred in which the Moon briefly covered Venus in the skies over parts of Indonesia.
Even when people observed the Moon and Venus at the same time, some locations offered a view of Venus disappearing and then reappearing, while in others the two celestial bodies merely appeared close together.
Why did the event in which the Moon covered Venus look so different depending on the observation site?
3-Line Summary
1. The phenomenon in which the Moon covered Venus occurred on September 14.
2. Western Sumatra had favorable conditions for observing the complete event.
3. Not every instance in which the two bodies appear close together is an occultation.
The Moment the Moon Passed Between Earth and Venus
A Venus occultation is a phenomenon in which the Moon passes precisely between Earth and Venus, temporarily hiding Venus behind the Moon’s disk. According to CNN Indonesia, citing an explanation from Bosscha Observatory, Venus appears near the Moon’s edge before being covered and is briefly hidden by the Moon. Visually, it resembles the scene just before a solar eclipse, when one celestial body draws very close to the edge of another.
In this event, the bright point beside the crescent Moon was not a star but Venus. Venus is commonly called the “morning star” from Earth, but the key point on this day was not the bright point itself; it was that the Moon passed in front of it and blocked the view. The mere appearance of the two celestial bodies close together does not qualify as an occultation.
The View Differed Between Sumatra and Java
A complete occultation could be seen only in parts of Sumatra, western Java, and parts of West Kalimantan in Indonesia. However, the observing conditions varied in greater detail from region to region. Tempo reported that western Sumatra was a favorable area for viewing the entire process of Venus appearing, disappearing, and appearing again.
By contrast, parts of Java and West Kalimantan were classified as having difficult or very difficult observing conditions. By the time Venus emerged from behind the Moon, it might already have descended below the horizon, making it difficult to see its reappearance. The farther south one went, such as to Padang and Lampung, and in Java regions such as Jakarta and Bandung, this problem reportedly became more pronounced.
This difference did not occur because the celestial bodies moved differently in each region, but because the viewing angle changed depending on where the observer was standing. Even for the same occultation, some regions could see the entire process, others only part of it, while still others might see a conjunction in which the Moon and Venus appeared close together without an occultation.
The Western Low Sky Was a Variable in Observation
The event took place in the western sky after sunset, from approximately 19:30 to 20:43. The times could vary depending on the location. In Banda Aceh, an example given by Tempo, Venus was expected to disappear at 19:29 and reappear 71 minutes later, at 20:41, but Venus’s altitude at reappearance was only 2.8 degrees above the horizon.
For that reason, during this event, what mattered more than whether one had a telescope was whether the western horizon was unobstructed and whether the weather and atmospheric conditions were favorable. Although the phenomenon could be seen with the naked eye, the low altitude meant that even within areas where observation was possible, the scene visible in practice differed. The combination of the crescent Moon and bright point formed by the Moon and Venus was the same, but the observation site determined whether one actually saw the “covering.”
References
Tags #VenusOccultation #Venus #Moon #AstronomicalPhenomenon #Occultation #Conjunction #CrescentMoon #MorningStar #BosschaObservatory #IndonesianAstronomy #September14 #NightSky