Observatory

A backyard radio telescope.

Every atom of neutral hydrogen in the galaxy hums at one radio frequency: 1420.406 MHz, a wavelength of 21 centimeters. Point an antenna anywhere along the Milky Way, average patiently, and the hum rises out of the noise. This page is where SignalDispatch stops reading the record and starts taking its own.

Instrument status: under constructionA backyard hydrogen-line telescope is being assembled in Kansas City: a one-meter dish, a 1420 MHz feed, a software-defined radio, and a Raspberry Pi that observes on a schedule. Until first light, the visuals below come from the professional surveys the dish will be checked against.

The sky in hydrogen

What the whole sky looks like on the hydrogen line.

Column density of neutral hydrogen across the entire sky, from the HI4PI survey — the combined work of two of the largest radio telescopes on Earth. The bright band is the plane of the Milky Way.

All-sky map of neutral hydrogen column density in galactic coordinates. A bright horizontal band across the middle marks the Milky Way's plane, with filamentary structure extending to high latitudes. — Neutral hydrogen, all sky, galactic coordinates (Aitoff projection). Data: HI4PI Collaboration (2016), via NASA SkyView. Rendered for SignalDispatch.

Spectra

The line moves. That is the galaxy turning.

Six spectra along the galactic plane from the Leiden/Argentine/Bonn survey. Each panel is one direction of gaze; the horizontal axis is velocity toward or away from us. The peaks shift and split from panel to panel because different spiral arms move at different speeds along each line of sight — measured this way, with instruments not much grander in principle than the one under construction, the Milky Way's rotation was mapped and the dark matter problem was born.

Six stacked hydrogen-line spectra at galactic longitudes 0, 30, 60, 90, 120, and 150 degrees. Each shows brightness temperature versus velocity; the peaks shift position and split into multiple components as longitude changes. — 21 cm brightness temperature vs. radial velocity at six galactic longitudes (b = 0°). Data: LAB survey, Kalberla et al. (2005), via the EU-HOU profile server. The raw spectra are available here exactly as retrieved.

First light

Where the backyard data will go.

When the dish sees the hydrogen peak for the first time, its spectrum publishes here next to the survey data it will be judged against. The build log will record what worked, what did not, and what the noise floor had to say about it.

Phase 0

Bench test: receiver chain verified indoors, bias tee powering the feed amplifier.

Phase 1

First light: the hydrogen peak, once, pointed at the galactic plane. Everything after this is refinement.

Phase 2

Autonomy: scheduled drift scans, calibrated and logged nightly without a human at the keyboard.

Phase 3

Publication: nightly spectra land on this page with observing conditions attached.

Data and credits

survey

HI4PI: a full-sky HI survey based on EBHIS and GASS

HI4PI Collaboration, Astronomy & Astrophysics 594, A116 (2016). All-sky map retrieved via NASA SkyView.

Open source

survey

The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI

Kalberla et al., Astronomy & Astrophysics 440, 775 (2005). Spectra retrieved from the EU-HOU LAB profile server at AIfA Bonn.

Open source

service

NASA SkyView Virtual Observatory

McGlynn et al., NASA GSFC. Survey imagery as a queryable service.

Open source

The renderings are reproducible: the fetch-and-render script lives in the SignalDispatch repository under tools/observatory/, and the retrieved data is committed beside the images, unmodified.