Know Your Actual Birthday: Astronomical Computation and Geospatial-Temporal Analytics in Python

are planning subsequent yr’s birthday celebrations for 3 associates: Gabriel, Jacques, and Camille. All three of them had been born in 1996, in Paris, France, so they are going to be 30 years previous subsequent yr in 2026. Gabriel and Jacques will occur to be in Paris on their respective birthdays, whereas Camille will likely be in Tokyo, Japan, throughout hers. Gabriel and Camille are likely to rejoice their birthdays in any given yr on the “official” days talked about on their beginning certificates — January 18 and Might 5, respectively. Jacques, who was born on February 29, prefers to rejoice his birthday (or civil anniversary) on March 1 in non-leap years.

We use leap years to maintain our calendar in sync with the Earth’s orbit across the Solar. A photo voltaic yr — the time it takes the Earth to finish one full orbit across the Solar — is roughly 365.25 days. By conference, the Gregorian calendar assigns one year to every yr, aside from leap years, which get three hundred and sixty six days to compensate for the fractional drift over time. This makes you marvel: will any of your folks be celebrating their birthday on the “actual” anniversary of their day of beginning, i.e., the day that the Solar will likely be in the identical place within the sky (relative to the Earth) because it was after they had been born? May or not it’s that your folks will find yourself celebrating turning 30 — a particular milestone — a day too quickly or a day too late?

The next article makes use of this birthday downside to introduce readers to some attention-grabbing and broadly relevant open-source information science Python packages for astronomical computation and geospatial-temporal analytics, together with skyfield, timezonefinder, geopy, and pytz. To achieve hands-on expertise, we are going to use these packages to unravel our enjoyable downside of precisely predicting the “actual birthday” (or date of photo voltaic return) in a given future yr. We are going to then focus on how such packages might be leveraged in different real-life functions.

Actual Birthday Predictor

Mission Setup

All implementation steps under have been examined on macOS Sequoia 15.6.1 and needs to be roughly related on Linux and Home windows.

Allow us to begin by organising the venture listing. We will likely be utilizing uv to handle the venture (see set up directions right here). Confirm the put in model within the Terminal:

uv --version

Initialize a venture listing referred to as real-birthday-predictor at an appropriate location in your native machine:

uv init --bare real-birthday-predictor

Within the venture listing, create a necessities.txt file with the next dependencies:

skyfield==1.53
timezonefinder==8.0.0
geopy==2.4.1
pytz==2025.2

Here’s a transient overview of every of those packages:

• skyfield supplies capabilities for astronomical computation. It may be used to compute exact positions of celestial our bodies (e.g., Solar, Moon, planets, and satellites) to assist decide rise/set instances, eclipses, and orbital paths. It depends on so-called ephemerides (tables of positional information for varied celestial our bodies extrapolated over a few years), that are maintained by organizations such because the NASA Jet Propulsion Laboratory (JPL). For this text, we are going to use the light-weight DE421 ephemeris file, which covers dates from July 29, 1899, via October 9, 2053.
• timezonefinder has capabilities for mapping geographical coordinates (latitudes and longitudes) to timezones (e.g., “Europe/Paris”). It could do that offline.
• geopy affords capabilities for geospatial analytics, resembling mapping between addresses and geographical coordinates. We are going to use it along with the Nominatim geocoder for OpenStreetMap information to map the names of cities and international locations to coordinates.
• pytz supplies capabilities for temporal analytics and time zone conversion. We are going to use it to transform between UTC and native instances utilizing regional daylight-saving guidelines.

We may even use a couple of different built-in modules, resembling datetime for parsing and manipulating date/time values, calendar for checking leap years, and time for sleeping between geocoding retries.

Subsequent, create a digital Python 3.12 surroundings contained in the venture listing, activate the surroundings, and set up the dependencies:

uv venv --python=3.12 
supply .venv/bin/activate
uv add -r necessities.txt

Examine that the dependencies have been put in:

uv pip record

Implementation

On this part, we are going to go piece by piece via the code for predicting the “actual” birthday date and time in a given future yr and placement of celebration. First, we import the required modules:

from datetime import datetime, timedelta
from skyfield.api import load, wgs84
from timezonefinder import TimezoneFinder
from geopy.geocoders import Nominatim
from geopy.exc import GeocoderTimedOut
import pytz
import calendar
import time

Then we outline the tactic, utilizing significant variable names and docstring textual content:

def get_real_birthday_prediction(
    official_birthday: str,
    official_birth_time: str,
    birth_country: str,
    birth_city: str,
    current_country: str,
    current_city: str,
    target_year: str = None
):
    """
    Predicts the "actual" birthday (photo voltaic return) for a given yr,
    accounting for the time zone on the beginning location and the time zone
    on the present location. Makes use of March 1 in non-leap years for the civil 
    anniversary if the official beginning date is February 29.
    """

Be aware that current_country and current_city collectively check with the placement at which the birthday is to be celebrated within the goal yr.

We validate the inputs earlier than working with them:

    # Decide goal yr
    if target_year is None:
        target_year = datetime.now().yr
    else:
        strive:
            target_year = int(target_year)
        besides ValueError:
            increase ValueError(f"Invalid goal yr '{target_year}'. Please use 'yyyy' format.")

    # Validate and parse beginning date
    strive:
        birth_date = datetime.strptime(official_birthday, "%d-%m-%Y")
    besides ValueError:
        increase ValueError(
            f"Invalid beginning date '{official_birthday}'. "
            "Please use 'dd-mm-yyyy' format with a sound calendar date."
        )

    # Validate and parse beginning time
    strive:
        birth_hour, birth_minute = map(int, official_birth_time.cut up(":"))
    besides ValueError:
        increase ValueError(
            f"Invalid beginning time '{official_birth_time}'. "
            "Please use 'hh:mm' 24-hour format."
        )

    if not (0 <= birth_hour <= 23):
        increase ValueError(f"Hour '{birth_hour}' is out of vary (0-23).")
    if not (0 <= birth_minute <= 59):
        increase ValueError(f"Minute '{birth_minute}' is out of vary (0-59).")

Subsequent, we use geopy with the Nominatim geocoder to establish the beginning and present places. To keep away from getting timeout errors, we set a fairly lengthy timeout worth of ten seconds; that is how lengthy our safe_geocode perform waits for the geocoding service to reply earlier than elevating a geopy.exc.GeocoderTimedOut exception. To be further secure, the perform makes an attempt the lookup process thrice with one-second delays earlier than giving up:

    geolocator = Nominatim(user_agent="birthday_tz_lookup", timeout=10)

    # Helper perform to name geocode API with retries
    def safe_geocode(question, retries=3, delay=1):
        for try in vary(retries):
            strive:
                return geolocator.geocode(question)
            besides GeocoderTimedOut:
                if try < retries - 1:
                    time.sleep(delay)
                else:
                    increase RuntimeError(
                        f"Couldn't retrieve location for '{question}' after {retries} makes an attempt. "
                        "The geocoding service could also be sluggish or unavailable. Please strive once more later."
                    )
    
    birth_location = safe_geocode(f"{birth_city}, {birth_country}")
    current_location = safe_geocode(f"{current_city}, {current_country}")

    if not birth_location or not current_location:
        increase ValueError("Couldn't discover coordinates for one of many places. Please test spelling.")

Utilizing the geographical coordinates of the beginning and present places, we determine the respective time zones and the UTC date and time at beginning. We additionally assume that people like Jacques, who had been born on February 29, will desire to rejoice their birthday on March 1 in non-leap years:

    # Get time zones
    tf = TimezoneFinder()
    birth_tz_name = tf.timezone_at(lng=birth_location.longitude, lat=birth_location.latitude)
    current_tz_name = tf.timezone_at(lng=current_location.longitude, lat=current_location.latitude)

    if not birth_tz_name or not current_tz_name:
        increase ValueError("Couldn't decide timezone for one of many places.")

    birth_tz = pytz.timezone(birth_tz_name)
    current_tz = pytz.timezone(current_tz_name)

    # Set civil anniversary date to March 1 for February 29 birthdays in non-leap years
    birth_month, birth_day = birth_date.month, birth_date.day
    if (birth_month, birth_day) == (2, 29):
        if not calendar.isleap(birth_date.yr):
            increase ValueError(f"{birth_date.yr} will not be a bissextile year, so February 29 is invalid.")
        civil_anniversary_month, civil_anniversary_day = (
            (3, 1) if not calendar.isleap(target_year) else (2, 29)
        )
    else:
        civil_anniversary_month, civil_anniversary_day = birth_month, birth_day

    # Parse beginning datetime in beginning location's native time
    birth_local_dt = birth_tz.localize(datetime(
        birth_date.yr, birth_month, birth_day,
        birth_hour, birth_minute
    ))
    birth_dt_utc = birth_local_dt.astimezone(pytz.utc)

Utilizing the DE421 ephemeris information, we calculate the place the Solar was (i.e., its ecliptic longitude) on the precise time and place the person was born:

    # Load ephemeris information and get Solar's ecliptic longitude at beginning
    eph = load("de421.bsp")  # Covers dates 1899-07-29 via 2053-10-09
    ts = load.timescale()
    solar = eph["sun"]
    earth = eph["earth"]
    t_birth = ts.utc(birth_dt_utc.yr, birth_dt_utc.month, birth_dt_utc.day,
                     birth_dt_utc.hour, birth_dt_utc.minute, birth_dt_utc.second)
    
    # Delivery longitude in tropical body from POV of beginning observer on Earth's floor
    birth_observer = earth + wgs84.latlon(birth_location.latitude, birth_location.longitude)
    ecl = birth_observer.at(t_birth).observe(solar).obvious().ecliptic_latlon(epoch='date')
    birth_longitude = ecl[1].levels

Be aware that, the primary time the road eph = load("de421.bsp") is executed, the de421.bsp file will likely be downloaded and positioned within the venture listing; in all future executions, the downloaded file will likely be used instantly. Additionally it is doable to switch the code to load one other ephemeris file (e.g., de440s.bsp, which covers years via January 22, 2150).

Now comes an attention-grabbing a part of the perform: we are going to make an preliminary guess of the “actual” birthday date and time within the goal yr, outline secure higher and decrease bounds for the true date and time worth (e.g., two days both facet of the preliminary guess), and carry out a binary search with early-stopping to effectively dwelling in on the true worth:

    # Preliminary guess for goal yr photo voltaic return
    approx_dt_local_birth_tz = birth_tz.localize(datetime(
        target_year, civil_anniversary_month, civil_anniversary_day,
        birth_hour, birth_minute
    ))
    approx_dt_utc = approx_dt_local_birth_tz.astimezone(pytz.utc)

    # Compute Solar longitude from POV of present observer on Earth's floor
    current_observer = earth + wgs84.latlon(current_location.latitude, current_location.longitude)

    def sun_longitude_at(dt):
        t = ts.utc(dt.yr, dt.month, dt.day, dt.hour, dt.minute, dt.second)
        ecl = current_observer.at(t).observe(solar).obvious().ecliptic_latlon(epoch='date')
        return ecl[1].levels

    def angle_diff(a, b):
        return (a - b + 180) % 360 - 180

    # Set secure higher and decrease bounds for search house
    dt1 = approx_dt_utc - timedelta(days=2)
    dt2 = approx_dt_utc + timedelta(days=2)

    # Use binary search with early-stopping to unravel for precise photo voltaic return in UTC
    old_angle_diff = 999
    for _ in vary(50):
        mid = dt1 + (dt2 - dt1) / 2
        curr_angle_diff = angle_diff(sun_longitude_at(mid), birth_longitude)
        if old_angle_diff == curr_angle_diff:  # Early-stopping situation
            break
        if curr_angle_diff > 0:
            dt2 = mid
        else:
            dt1 = mid
        old_angle_diff = curr_angle_diff

    real_dt_utc = dt1 + (dt2 - dt1) / 2

See this article for extra examples of utilizing binary search and to know why this algorithm is a vital one for information scientists to grasp.

Lastly, the date and time of the “actual” birthday recognized by the binary search is transformed to the present location’s time zone, formatted as wanted, and returned:

    # Convert to present location's native time and format output
    real_dt_local_current = real_dt_utc.astimezone(current_tz)
    date_str = real_dt_local_current.strftime("%d/%m")
    time_str = real_dt_local_current.strftime("%H:%M")

    return date_str, time_str, current_tz_name

Testing

Now we’re able to foretell the “actual” birthdays of Gabriel, Jacques, and Camille in 2026.

To make the perform output simpler to digest, here’s a helper perform we are going to use to pretty-print the outcomes of every question:

def print_real_birthday(
    official_birthday: str,
    official_birth_time: str,
    birth_country: str,
    birth_city: str,
    current_country: str,
    current_city: str,
    target_year: str = None):
    """Fairly-print output whereas hiding verbose error traces."""

    print("Official birthday and time:", official_birthday, "at", official_birth_time)

    strive:
        date_str, time_str, current_tz_name = get_real_birthday_prediction(
            official_birthday,
            official_birth_time,
            birth_country,
            birth_city,
            current_country,
            current_city,
            target_year
        )

        print(f"In yr {target_year}, your actual birthday is on {date_str} at {time_str} ({current_tz_name})n")

    besides ValueError as e:
        print("Error:", e)

Listed below are the check circumstances:

# Gabriel
print_real_birthday(
    official_birthday="18-01-1996", 
    official_birth_time="02:30",
    birth_country="France",
    birth_city="Paris",
    current_country="France",
    current_city="Paris",
    target_year="2026"
)

# Jacques
print_real_birthday(
    official_birthday="29-02-1996", 
    official_birth_time="05:45",
    birth_country="France",
    birth_city="Paris",
    current_country="France",
    current_city="Paris",
    target_year="2026"
)

# Camille
print_real_birthday(
    official_birthday="05-05-1996", 
    official_birth_time="20:30",
    birth_country="Paris",
    birth_city="France",
    current_country="Japan",
    current_city="Tokyo",
    target_year="2026"
)

And listed below are the outcomes:

Official birthday and time: 18-01-1996 at 02:30
In yr 2026, your actual birthday is on 17/01 at 09:21 (Europe/Paris)

Official birthday and time: 29-02-1996 at 05:45
In yr 2026, your actual birthday is on 28/02 at 12:37 (Europe/Paris)

Official birthday and time: 05-05-1996 at 20:30
In yr 2026, your actual birthday is on 06/05 at 09:48 (Asia/Tokyo)

As we see, the “actual” birthday (or second of photo voltaic return) is completely different from the official birthday for all three of your folks: Gabriel and Jacques may theoretically begin celebrating a day earlier than their official birthdays in Paris, whereas Camille ought to attend yet one more day earlier than celebrating her thirtieth in Tokyo.

As a less complicated different to following the steps above, the writer of this text has created a Python library referred to as solarius to attain the identical end result (see particulars right here). Set up the library with pip set up solarius or uv add solarius and use it as proven under:

from solarius.mannequin import SolarReturnCalculator

calculator = SolarReturnCalculator(ephemeris_file="de421.bsp")

# Predict with out printing
date_str, time_str, tz_name = calculator.predict(
    official_birthday="18-01-1996",
    official_birth_time="02:30",
    birth_country="France",
    birth_city="Paris",
    current_country="France",
    current_city="Paris",
    target_year="2026"
)

print(date_str, time_str, tz_name)

# Or use the comfort printer
calculator.print_real_birthday(
    official_birthday="18-01-1996",
    official_birth_time="02:30",
    birth_country="France",
    birth_city="Paris",
    current_country="France",
    current_city="Paris",
    target_year="2026"
)

In fact, there’s extra to birthdays than predicting photo voltaic returns — these particular days are steeped in centuries of custom. Here’s a quick video on the fascinating origins of birthdays:

Past Birthdays

The intention of the above part was to offer readers a enjoyable and intuitive use case for making use of the assorted packages for astronomical computation and geospatial-temporal analytics. Nevertheless, the usefulness of such packages goes far past predicting birthdays.

For instance, all of those packages can be utilized for different circumstances of astronomical occasion prediction (e.g., figuring out when a dawn, sundown, or eclipse will occur on a future date in a given location). Predicting the motion of satellites and different celestial our bodies may additionally play an essential half in planning house missions.

The packages may be used to optimize the deployment of photo voltaic panels in a selected location, resembling a residential neighborhood or a industrial web site. The target can be to foretell how a lot daylight is more likely to fall on that location at completely different instances of the yr and use this information to regulate the location, tilt, and utilization schedules of the photo voltaic panels for optimum power seize.

Lastly, the packages might be leveraged for historic occasion reconstruction (e.g., within the context of archaeological or historic analysis, and even authorized forensics). The target right here can be to recreate the sky circumstances for a particular previous date and placement to assist researchers higher perceive the lighting and visibility circumstances at the moment.

Finally, by combining these open-source packages and built-in modules in varied methods, it’s doable to unravel attention-grabbing issues that reduce throughout a lot of domains.