And here is an explanation:
Like the Latin Mass and meatless Fridays, the indulgence was one of the traditions decoupled from mainstream Catholic practice in the 1960s by the Second Vatican Council, the gathering of bishops that set a new tone of simplicity and informality for the church. Its revival has been viewed as part of a conservative resurgence that has brought some quiet changes and some highly controversial ones, like Pope Benedict XVI’s recent decision to lift the excommunications of four schismatic bishops who reject the council’s reforms.The indulgence is among the less noticed and less disputed traditions to be restored. But with a thousand-year history and volumes of church law devoted to its intricacies, it is one of the most complicated to explain.
I was wondering, as an astronomer, on the issue of "length of days" in the afterlife (by the way, Islam also has a temporary place for souls, called Barzakh, until Judgment Day) and how indulgences take that into account. A Purgatory (or Barzakh) planet with the same orbital period as the Earth? Well...Slate has a response article and it talks about some of these issues:
According to church teaching, even after sinners are absolved in the confessional and say their Our Fathers or Hail Marys as penance, they still face punishment after death, in Purgatory, before they can enter heaven. In exchange for certain prayers, devotions or pilgrimages in special years, a Catholic can receive an indulgence, which reduces or erases that punishment instantly, with no formal ceremony or sacrament.There are partial indulgences, which reduce purgatorial time by a certain number of days or years, and plenary indulgences, which eliminate all of it, until another sin is committed. You can get one for yourself, or for someone who is dead. You cannot buy one — the church outlawed the sale of indulgences in 1567 — but charitable contributions, combined with other acts, can help you earn one. There is a limit of one plenary indulgence per sinner per day.
How do Catholics calculate spiritual sentences in the first place?
They don't. A Spanish theologian from the late Middle Ages once argued that the average Christian spends 1000 to 2000 years in purgatory (according to Stephen Greenblatt's Hamlet in Purgatory). But there's no official take on the average sentence. According to the church, only God knows the exact amount of time a person must spend in purgatory before attaining a state of purity. It's assumed, however, that the severity of one's punishment will be directly proportional to the severity of the crime. (See this Explainer for more about the gradations of Catholic sins.)
Contrary to what the Times article suggests, partial indulgences don't come with specific amounts of time off for good behavior. Because it's generally understood that time works differently in purgatory than it does on Earth, "five weeks off" has no practical meaning in the afterlife. Properly speaking, purgatory is a process rather than a place—the popular image of purgatory as something with spatial and temporal dimensions dates back to medieval times but isn't actually part of official church doctrine.