---
url: /mosaic/examples/gaia.md
---
# Gaia Star Catalog

A 5M row sample of the 1.8B element Gaia star catalog.
A `raster` sky map reveals our Milky Way galaxy. Select high parallax stars in the histogram to reveal a
[Hertzsprung-Russel diagram](https://en.wikipedia.org/wiki/Hertzsprung%E2%80%93Russell_diagram)
in the plot of stellar color vs. magnitude on the right.

*You may need to wait a few seconds for the dataset to load.*

## Specification

```py \[Python]
import vgplot as vg

gaia = vg.table(
    "-- compute u and v with natural earth projection\nWITH prep AS (\n  SELECT\n    radians((-l + 540) % 360 - 180) AS lambda,\n    radians(b) AS phi,\n    asin(sqrt(3)/2 * sin(phi)) AS t,\n    t^2 AS t2,\n    t2^3 AS t6,\n    *\n  FROM 'https://pub-1da360b43ceb401c809f68ca37c7f8a4.r2.dev/data/gaia-5m.parquet'\n  WHERE parallax BETWEEN -5 AND 20 AND phot_g_mean_mag IS NOT NULL AND bp_rp IS NOT NULL\n)\nSELECT\n  (1.340264 * \"lambda\" * cos(t)) / (sqrt(3)/2 * (1.340264 + (-0.081106 * 3 * t2) + (t6 * (0.000893 * 7 + 0.003796 * 9 * t2)))) AS u,\n  t * (1.340264 + (-0.081106 * t2) + (t6 * (0.000893 + 0.003796 * t2))) AS v,\n  * EXCLUDE('t', 't2', 't6')\nFROM prep"
)

brush = vg.selection.crossfilter()
bandwidth = vg.param(0)
pixelSize = vg.param(2)
scaleType = vg.param("sqrt")

view = vg.hconcat(
    vg.vconcat(
        vg.plot(
            vg.raster(
                data=gaia,
                filter_by=brush,
                x="u",
                y="v",
                fill="density",
                bandwidth=bandwidth,
                pixel_size=pixelSize,
            ),
            vg.interval_xy(pixel_size=2, bind=brush),
            vg.xy_domain("Fixed"),
            vg.color_scale(scaleType),
            vg.color_scheme("viridis"),
            vg.width(440),
            vg.height(250),
            vg.margin_left(25),
            vg.margin_top(20),
            vg.margin_right(1),
        ),
        vg.hconcat(
            vg.plot(
                vg.rect_y(
                    data=gaia,
                    filter_by=brush,
                    x=vg.bin("phot_g_mean_mag"),
                    y=vg.count(),
                    fill="steelblue",
                    inset=0.5,
                ),
                vg.interval_x(bind=brush),
                vg.x_domain("Fixed"),
                vg.y_scale(scaleType),
                vg.y_grid(True),
                vg.width(220),
                vg.height(120),
                vg.margin_left(65),
            ),
            vg.plot(
                vg.rect_y(
                    data=gaia,
                    filter_by=brush,
                    x=vg.bin("parallax"),
                    y=vg.count(),
                    fill="steelblue",
                    inset=0.5,
                ),
                vg.interval_x(bind=brush),
                vg.x_domain("Fixed"),
                vg.y_scale(scaleType),
                vg.y_grid(True),
                vg.width(220),
                vg.height(120),
                vg.margin_left(65),
            ),
        ),
    ),
    vg.hspace(10),
    vg.plot(
        vg.raster(
            data=gaia,
            filter_by=brush,
            x="bp_rp",
            y="phot_g_mean_mag",
            fill="density",
            bandwidth=bandwidth,
            pixel_size=pixelSize,
        ),
        vg.interval_xy(pixel_size=2, bind=brush),
        vg.xy_domain("Fixed"),
        vg.color_scale(scaleType),
        vg.color_scheme("viridis"),
        vg.y_reverse(True),
        vg.width(230),
        vg.height(370),
        vg.margin_left(25),
        vg.margin_top(20),
        vg.margin_right(1),
    ),
)

```