See what a galaxy is made of

AstroVista Lite fits the isophotes of galaxies, finds and measures the stars and galaxies around them, masks what is in the way and does arithmetic on whole images, all in one window. It is simple enough for a first class in astronomy and useful in everyday research.

Install Start the tutorial Source on GitHub

The AstroVista Lite window: a Hubble image of the galaxy UGC 12517 with green fitted isophotes, the buffers and layers on the left, the ELLIPROF tool on the right and the terminal below — The galaxy UGC 12517 (Hubble Space Telescope, near infrared) with its 23 fitted isophotes (green). Masked pixels are red; the terminal below records every step as a command.

What it does

One window for the whole measurement

Isophote fitting

ELLIPROF fits ellipses to a galaxy's light from the centre outwards. You get a profile table, plots, the model galaxy and the residual image.

A source finder

Finds the stars and galaxies in the image and measures their position, shape, flux, magnitude and size, with SExtractor's names. A sortable catalogue and plots come with it.

Masks

Draw circles, ellipses, boxes, polygons and brush strokes, then turn and resize them before applying. You can also mask every found source at once. Undo and redo work throughout.

Image arithmetic

Write [3] = [1] - [2], median, where and clip: formulas worked out pixel by pixel over whole images.

A terminal

Every action is a command, echoed as it runs. Save a session and run it again later, or give it to a class.

Built to teach

A first lesson, recipes, a FAQ and a ? beside every setting, all in the built-in documentation (F1).

Install

One command, on Linux or macOS

pip install AstroVista
astrovista --example        # the UGC 12517 example, shipped with the package
astrovista galaxy.fits      # or your own images

Python 3.10 or later. Everything comes with pip install, the source finder included. pip install astrovista is the same: PyPI ignores capitals. A virtual environment keeps it apart from your other Python programs:

python3 -m venv ~/astrovista-env
source ~/astrovista-env/bin/activate
pip install AstroVista

Supported systems

	Supported
macOS	13 (Ventura) or later, Apple silicon and Intel
Linux, x86_64	glibc 2.34 or later: Ubuntu 22.04+, Debian 12+, Fedora 35+, RHEL / Rocky / Alma 9+
Linux, ARM	glibc 2.39 or later: Ubuntu 24.04+
Windows	not yet (WSL2 with the Linux instructions should work, but is untested)
Python	3.10 to 3.13; 3.14 works too, but SEP is then compiled during the install, which needs a C compiler

When Python is missing or too old

Check with python3 --version. If it is older than 3.10, or missing, a conda environment brings its own Python (Miniforge is a small, free conda installer):

conda create -n astrovista -c conda-forge python=3.12 pip
conda activate astrovista
pip install AstroVista

On an older system where pip finds no Qt (No matching distribution found for PySide6), take Qt and the scientific libraries from conda-forge and only AstroVista from pip:

conda create -n astrovista -c conda-forge python=3.12 pip pyside6 pyqtgraph numpy scipy astropy matplotlib sep
conda activate astrovista
pip install AstroVista

Starting it

Images and masks can be loaded from the command line: -i puts images into buffers 1, 2, … and -m adds mask layers.

astrovista -i galaxy.fits "frame.fits[sci]" -m galaxy.dmask
astrovista --run session.txt     # replay a file of commands

On a minimal Linux system (a server, WSL, a container), Qt may report that it could not load the Qt platform plugin "xcb". Install the libraries every desktop already has: sudo apt install libxcb-cursor0 libxkbcommon-x11-0 libegl1 libgl1 libfontconfig1 libdbus-1-3 (Debian, Ubuntu), or sudo dnf install xcb-util-cursor libxkbcommon-x11 mesa-libEGL mesa-libGL fontconfig dbus-libs (Fedora).

A tour

What you will see

Start here

The welcome screen opens the example galaxy, your own FITS image, or the First lesson. On the left, buffers hold images and layers hold what is drawn over them. The image is in the middle. On the right, the Inspector, the Tools, the Results and the FITS header sit in tabs. The terminal is below.

The welcome screen with buttons to open the example, open an image, or start the first lesson

Look at the light

Faint light needs a stretched scale: Log, Asinh or a histogram equalisation. Choose the limits from percentiles or ZScale, or drag them on the histogram. Pick from twelve colour maps, and drag with the right mouse button for contrast and bias. None of this changes a pixel value.

The galaxy in the viridis colour map with the histogram and the colour bar under the image

Contours

Lines of equal brightness, with DS9's settings: the number of levels, linear or log spacing, the smoothing, and the line colour and width. Each value can be edited.

Inspect a pixel

The Inspector shows the pixel under the cursor or the crosshair: its value, its sky position (RA, Dec), a magnified view, and the statistics of the pixels around it.

The crosshair over the galaxy and the Inspector showing the pixel value, RA and Dec and a magnified view

Mask what is in the way

Draw a shape and it waits, in magenta, until you apply it. Drag it to move it, drag its squares to resize it, and turn it with the round handle or the [ ] keys. Press Enter to apply it or Esc to cancel. Alt or Shift unmasks.

A magenta ellipse turned by 35 degrees, with square handles for resizing and a round handle for turning, waiting to be applied

Fit the isophotes

Press Fit isophotes. ELLIPROF follows the galaxy's light outwards from R0 to R1. The model and the residual go into the buffers you choose; by default only free buffers are offered.

Green isophotes fitted to UGC 12517 with the ELLIPROF tool on the right

Read the profile

Plot the intensity, ellipticity, position angle or the higher harmonics against the radius or R^¼. Tick R¼ law to fit de Vaucouleurs' law; for this galaxy, R_e ≈ 126 pixels with a scatter of 0.07 mag. Save the plot as a PNG, or the table as an aligned CSV file.

Find and measure sources

The Source finder detects every star and galaxy in the image and measures it with SEP, which implements SExtractor's algorithms. Click a source to find its row; sort the catalogue by any column; plot one column against another.

Cyan ellipses around the detected sources and the sortable catalogue on the right

Look at what is left

The residual, the image minus the model, shows what a smooth ellipse cannot describe: dust lanes, discs, shells and companions. Tick Blink and press ← → to switch between the image, the model and the residual. When zoomed in, blinking keeps the same patch of sky through the WCS.

The residual image after the model galaxy is subtracted

Type it, keep it, run it again

Every button runs a command that you can also type: arithmetic, statistics, masks, fits. Tab completes commands, buffers and file names. File ▸ Save the commands keeps the session as a script.

The terminal showing arithmetic commands and their statistics, with the ratio image displayed

Figures for your paper or your class

Export what you measured

The profile and the plots are saved as PNG figures made with matplotlib. Tables are saved as CSV files whose columns line up in any text editor, and read back with pandas or astropy. Isophotes can be exported as DS9 regions.

Results ▸ Profile ▸ Save PNG…

A matplotlib scatter plot of FLUX_RADIUS against MAG_AUTO for the found sources — Results ▸ Plots ▸ Save PNG…: stars form the narrow sequence at the bottom

Learn

Help is built in

Press F1 for the documentation. It includes a thirty-minute First lesson, recipes, image arithmetic in detail, a glossary, a FAQ, troubleshooting, every command, and every setting explained. The ? beside each setting opens its own entry.

On this site: the tutorial walks through a whole measurement with questions for learners; The terminal explains how commands are written; the Command reference gives every command with its keywords and an example; and Commands & recipes collects worked examples.

The built-in documentation window showing the first lesson

Credits

Citing and credits

John Tonry. ELLIPROF, the isophote fitting at the heart of AstroVista Lite, was originally developed by John Tonry as part of MONSTA; it is used here through the elliprof package, which compiles his original code unchanged. The terminal follows the command language of MONSTA, John Tonry's image analysis and plotting system, which joined Vista (originally by Richard Stover and Tod Lauer, with image display by John Tonry) and Mongo (by John Tonry). The commands of AstroVista Lite are new code written in that style.

If AstroVista Lite helps your work or your teaching, please cite its repository:

Kourkchi, E., AstroVista Lite, https://github.com/ekourkchi/AstroVista-Lite

GitHub's Cite this repository button gives the same. For the measurements, please also cite:

elliprof, for the isophotes;
SEP (Barbary 2016, JOSS 1, 58) and SExtractor (Bertin & Arnouts 1996, A&AS 117, 393), for the source finder.

Built with Qt for Python (PySide6), pyqtgraph, matplotlib, NumPy, SciPy and Astropy. The example image of UGC 12517 (HST WFC3/IR, F110W) and its mask come from the elliprof example. AstroVista Lite is free software under the MIT licence.