Pluto PS1 NIR Finder

pluto_ps1_nir_finder.py creates a printable finder chart for Pluto using:

• Pluto position at a chosen date/time (Astropy ephemerides)
• Pan-STARRS DR1 stars (II/349/ps1) for RA/Dec and brightness
• r-band magnitudes only for star size scaling
• Black-on-white atlas style with RA/Dec grid, N/E arrows, and Pluto marker

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1) Get the code from GitHub

Repository:

• https://github.com/blackhaz/pluto_ps1_nir_finder

Clone with Git:

git clone https://github.com/blackhaz/pluto_ps1_nir_finder.git
cd pluto_ps1_nir_finder

If you do not use Git, you can also download ZIP from GitHub:

1. Open the repository URL above
2. Click Code → Download ZIP
3. Extract ZIP
4. Open terminal in extracted folder

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2) Requirements

• Python 3.10+ (3.11 recommended)
• Internet access (queries Pan-STARRS through CDS VizieR)
• Python packages:
  • numpy
  • matplotlib
  • astropy
  • astroquery

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3) Install on Windows

3.1 Install system tools

1. Install Python from https://www.python.org/downloads/windows/
   • During install, check Add Python to PATH.
2. (Optional) Install Git: https://git-scm.com/download/win

3.2 Create virtual environment and install dependencies

Open PowerShell in the project folder and run:

py -3 -m venv .venv
.\.venv\Scripts\Activate.ps1
python -m pip install --upgrade pip
pip install numpy matplotlib astropy astroquery

If PowerShell blocks activation, run once:

Set-ExecutionPolicy -Scope CurrentUser RemoteSigned

3.3 Test installation

python pluto_ps1_nir_finder.py --help

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4) Install on macOS

4.1 Install system tools

If needed:

xcode-select --install

Install Homebrew (optional but recommended):

• https://brew.sh

Install Python + Git:

brew install python git

4.2 Create virtual environment and install dependencies

python3 -m venv .venv
source .venv/bin/activate
python -m pip install --upgrade pip
pip install numpy matplotlib astropy astroquery

4.3 Test installation

python pluto_ps1_nir_finder.py --help

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5) Install on Linux

5.1 Install system tools

Debian/Ubuntu

sudo apt update
sudo apt install -y python3 python3-venv python3-pip git

Fedora

sudo dnf install -y python3 python3-pip git

Arch

sudo pacman -S --needed python python-pip git

5.2 Create virtual environment and install dependencies

python3 -m venv .venv
source .venv/bin/activate
python -m pip install --upgrade pip
pip install numpy matplotlib astropy astroquery

5.3 Test installation

python pluto_ps1_nir_finder.py --help

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6) Basic usage

Required argument:

• --datetime observation date/time in ISO-8601 format

Example:

python pluto_ps1_nir_finder.py \
  --datetime 2026-04-10T00:00:00+00:00 \
  --fov 3.0 \
  --rmag-limit 15.0 \
  --dpi 240 \
  --output pluto_finder.png

This creates pluto_finder.png in the current folder.

Topocentric (observer-specific) example:

python pluto_ps1_nir_finder.py \
  --datetime 2026-04-10T00:00:00+00:00 \
  --observer-lat 52.5200 --observer-lon 13.4050 --observer-elevation-m 35 \
  --fov 1.0 --rmag-limit 17.5 \
  --output pluto_finder_berlin.png

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7) CLI options

--datetime         Required. ISO datetime, e.g. 2026-07-15T22:30:00+00:00
--fov              Field width in degrees (default: 1.2)
--rmag-limit       Faintest r magnitude to include (default: 18.0)
--dpi              Output DPI (default: 240)
--output           Output image filename (default: pluto_finder_ps1_r_printable.png)
--center-ra        Optional fixed chart center RA in deg
--center-dec       Optional fixed chart center Dec in deg
--center-datetime  Optional fixed center = Pluto position at this datetime
--observer-lat     Optional observer latitude in deg (for topocentric Pluto)
--observer-lon     Optional observer longitude in deg, east positive
--observer-elevation-m  Optional observer elevation in meters (default: 0)

Centering behavior

• Default: chart center follows Pluto at --datetime
• For motion studies (same star field, Pluto moves), use:
  • --center-datetime (recommended), or
  • --center-ra and --center-dec

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8) Show Pluto motion between dates (recommended workflow)

Generate two charts with the same center:

python pluto_ps1_nir_finder.py \
  --datetime 2026-04-10T00:00:00+00:00 \
  --center-datetime 2026-04-10T00:00:00+00:00 \
  --fov 0.8 --rmag-limit 17.5 --output chart_2026-04-10.png

python pluto_ps1_nir_finder.py \
  --datetime 2026-05-10T00:00:00+00:00 \
  --center-datetime 2026-04-10T00:00:00+00:00 \
  --fov 0.8 --rmag-limit 17.5 --output chart_2026-05-10.png

Now the stars stay fixed and Pluto position shifts.

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9) Star size model used

Star diameters are atlas-style, based on r magnitude:

• mag 0 → 20 mm
• mag 1 → 10 mm
• mag 3 → 5 mm
• mag 4 → 2 mm

Then all diameters are scaled by the script constant:

• STAR_DIAMETER_SCALE = 2.0

Faintest stars at --rmag-limit are forced to at least 2 output pixels diameter (because of the 2x scale).

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10) Troubleshooting

No chart or “No Pan-STARRS DR1 sources returned”

• Increase --fov (e.g., 1.2 → 3.0)
• Use a fainter --rmag-limit (e.g., 15 → 18)
• Check internet/firewall/proxy

Pluto seems not moving when date changes

This is expected if chart center follows Pluto (default). Use fixed center:

• --center-datetime <baseline_date> or
• --center-ra ... --center-dec ...

Pluto position does not match Stellarium

Use the same time, location, and coordinate mode when comparing:

• Set --datetime exactly (including timezone offset)
• If needed, pass observer site:
  • --observer-lat
  • --observer-lon
  • --observer-elevation-m
• In Stellarium, compare using J2000/ICRF-like equatorial coordinates (not apparent-of-date readout)

The script computes Pluto as an Earth-observed apparent position (GCRS) and uses Pan-STARRS J2000 star coordinates. Small arcsecond-level differences may still occur vs. Stellarium due to ephemeris/model differences.

ModuleNotFoundError

Make sure your virtual environment is activated and dependencies are installed:

pip install numpy matplotlib astropy astroquery

PowerShell activation blocked

Use:

Set-ExecutionPolicy -Scope CurrentUser RemoteSigned

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11) Quick verification command

python pluto_ps1_nir_finder.py \
  --datetime 2026-04-10T00:00:00+00:00 \
  --fov 0.8 --rmag-limit 17.5 \
  --output test_chart.png

If successful, the script prints:

Saved finder chart: test_chart.png