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AI Prompts for Moon VOC Planning

Astrological calculation with LLM prompts for any AI platform for accurate Moon Void of Course (VOC) planning.

Even for people who don't closely follow astrology, Moon VOC conditions, like Mercury Retrograde, are known to be factors for "astrological bad days", when things don't go according to plan. Late arrivals, missed appointments, and in general, "unexpected outcomes" can be anticipated when the Moon is VOC. The Moon goes void-of-course every two to three days, when it makes no more major angles with planets before changing signs. Traditional astrology treats these periods as unfavorable for starting new ventures: decisions made during void-of-course Moon periods tend to require revision, or do not develop as expected. Moon VOC periods are "mundane"; that is, they apply to everyone in the world and are not dependent on your personal birth data.

With a Moon VOC Planner, you'll know the times of Moon VOC periods so you can pick the best times for activities. Moon VOC times are widely published on the web so any LLM equipped with web search can find Moon VOC times; however, an LLM may get confused about time zones or exact dates. It is safer to use a dedicated astrological calculation tool than to rely on a LLM.

In AstroPrompt, the Moon VOC Planner view lists every Moon void-of-course period in a chosen month with exact start and end times in the user's local time zone. With accurate Moon VOC times, you can ask an LLM whether specfic activities are wise during the VOC times.

For an introduction to the process, see calculation-first AI astrology workflow.

Before you get started

Moon VOC Planner is an option in the AstroPrompt navigation bar, and the fastest way to get a result is to use AstroPrompt. The tutorial below explains how to obtain the same result from any LLM yourself. To do it yourself you will need to install Astrolog, write the chart output to a file, and combine the Astrolog dataset with the prompts shown below. AstroPrompt makes the workflow easier: it runs Astrolog automatically, lets you pick from popular LLMs (such as OpenAI GPTs, Claude Opus, or Google Gemini), and streamlines the prompt assembly. For advanced users, AstroPrompt Pro lets you edit the prompts so you can customize tone, interpretation, or output structure. Try AstroPrompt now; it is FREE.

Moon VOC Planner

The Moon VOC Planner shows void-of-course Moon periods for a calendar month. Each entry includes the date and time the VOC begins, the date and time the Moon enters the next sign (which ends the VOC), the duration of the VOC period, and the sign transition involved.

No birth data is required. The schedule is the same for everyone in a given timezone, since it is a sky event rather than a personal transit. The chat asks "What can go wrong during a void-of-course Moon?" and the full report offers to generate an ICS file, a PDF calendar page, or a Google Sheets dashboard.

How to get an accurate LLM response

AI can't calculate planetary positions accurately or read an ephemeris reliably. To get an accurate and reliable interpretation, you must provide this astrological data:

  • The full month of VOC periods, with start time, end time, duration, and sign transitions.
  • Times in the user's display timezone, not UTC.
  • Inclusion of any VOC periods that span midnight from the previous month or into the next month, so no period is truncated at the boundary.

Astrolog commands

The Moon VOC Planner runs one Astrolog command per day across a window from the last day of the previous month through the first day of the next month, then parses the output for VOC markers:

astrolog -q {month} {day} {year} 12:00pm -z {tz} -z0 0 -d
  • `-q` runs Astrolog in quick chart mode, anchored at noon for each day. The reference time is irrelevant for VOC detection because the parser looks at aspect events across the day.
  • `-z {tz}` sets the display timezone for the day's events. AstroPrompt converts the user's IANA timezone to Astrolog's inverted numeric format.
  • `-z0 0` disables Astrolog's daylight-savings auto-adjust, since AstroPrompt has already pre-computed the correct offset.
  • `-d` produces the daily aspect calendar, which includes Moon void-of-course markers (v/c) and Moon sign-change events (enters).

The command runs for every day in the window. The parser collects only lines containing v/c or enters, threads them into complete VOC periods (start time when the Moon's last major aspect completes, end time when the Moon enters the next sign), and outputs the duration and sign transitions.

The window deliberately includes the last day of the previous month and the first day of the next month so that a VOC period spanning a month boundary is captured at both ends.

Prompts

Astrological data is combined with a user's prompt to create the context for a question that begins an AI chat. The LLM receives everything (including its responses to previous questions) as a single context block, but it is easier for us if we assemble the context from three specific prompts: a system prompt, a data description prompt, and a user prompt that asks for a report. In AstroPrompt Pro, you can edit and save each of these prompts to customize tone, interpretation, or output structure. For this tutorial, combine each of these prompts with the astrological data and then paste the entire block into the AI chat.

System Prompt

The foundational instruction that sets the AI's overall tone, style, and approach, which applies to every message in the conversation. The default produces balanced, measured analysis. You can change it to anything: terse bullet-point summaries, a specific cultural or traditional framework, a particular language, or even a lengthy style guide that reproduces your own voice for client-facing work. This is the most powerful lever for fundamentally changing the character of the AI's responses.

The system prompt is shared across every AstroPrompt view:

When generating astrological forecasts, do not use rhetorical or
        persuasive devices typical of popular horoscope writing. Avoid inserting
        emotional appeals or literary devices. Avoid the following:

        • Imperatives and exhortative tone (e.g., "Embrace change," "Let go of
          the past," "Surround yourself with warmth")
        • Evocative metaphors and symbolic language (e.g., "personal
          renaissance," "magnetic energy," "mirror of the soul")
        • Overly enthusiastic, poetic, or cute phrasing
        • Vague affirmations or inspirational advice not grounded in planetary
          positions

        Instead, use a neutral, informative tone. Focus on:

        • Relevant planetary influences and their timing
        • Which life areas are affected and how
        • Expected themes based on astrological interpretation
        • Possibility framing using modal verbs (e.g., may, might, could)
          without interpretive flourish
        • Objective language suitable for readers seeking analysis rather than
          affirmation

        Structure any planner forecast by timeline or topic (e.g., career,
        relationships, health).

AstroPrompt adds a terminology directive (advanced or beginner) based on its settings.

Data Description

This prompt tells the AI what the raw astrological data actually represents. This is how the AI understands the underlying dataset. Advanced users can use this to direct the AI's attention toward specific technical elements they care about most.

After the parsed VOC schedule, AstroPrompt appends this description:

This data contains Moon Void-of-Course (VOC) periods for the selected
        month, including the date and time each VOC period begins, when the Moon
        enters the next sign, the duration of each VOC period, and the sign
        transitions involved.

The "duration" and "sign transitions" hints prepare the model to format calendar exports correctly when the user requests an ICS or PDF.

Full Report Prompt

AstroPrompt provides detailed instructions when a user wants a full report. This is typically the longest prompt and has the greatest single impact on report quality and structure. The default walks the AI through a specific analytical sequence. You can replace this entirely as you wish, for example, to focus the report on career and finance, restructure it around specific techniques, or direct the LLM to use the point of view of a favored lineage or tradition.

The Moon VOC Planner report diffwers from other AstroPrompt reports: it does not produce an interpretation. It asks the user to pick a delivery format and produces only the chosen export:

Given this dataset of Moon Void-of-Course periods for the month,
        including dates, times, durations, and sign transitions, offer me the
        option to choose one of the following output formats:

        1. A downloadable ICS calendar file containing each VOC period as its
           own event. The file should be properly formatted for import into
           Google Calendar, Apple Calendar, and Outlook.
        2. A one-page downloadable PDF calendar page for the month with days as
           boxes on a grid and VOC times only (no sign changes).
        3. A Google Sheets-ready monthly dashboard.

        Ask which output I want (ICS, PDF, or Sheets). Then generate only the
        selected output.

The "ask first, then generate only the selected output" framing is a deliberate constraint: the model is expected to wait for the user's choice rather than producing all three formats. This keeps the response focused and avoids generating three artifacts when only one is wanted.

Unique features of the Moon VOC Planner prompt

  • VOC detection runs across a 32-day or longer window so periods spanning month boundaries are caught at both ends.
  • No birth data is required, since the VOC schedule is a sky event affecting everyone in the timezone.
  • All times are displayed in the user's local timezone, not UTC, with daylight-savings handled correctly per date.
  • The full report prompt is a delivery-format selector rather than an interpretation: the dataset is treated as a calendar artifact, not an essay topic.
  • The prompt explicitly names ICS, PDF, and Google Sheets as accepted formats, anchoring the model to deliverables that exist.

What's Next

This was written in May 2026, describing the data and prompts used in AstroPrompt version 1.0. Astrologers are just beginning to explore the capabilities of AI as a tool for astrological insight. If you've got suggestions for a better dataset or improved prompts, I'd love to hear from you. Email me at hello@timecasters.com.