TARGET 06 · l = 180°, b = 0° · Taurus/Auriga border, a few degrees east of Elnath; the Crab Nebula is nearby
Galactic anticentre, l = 180°
Straight away from the centre, where circular rotation gives no radial velocity at all. A narrow line near zero makes it the best calibration check on the sky.
- RA / Dec (J2000)
- 05h 45m 37s
+28.9° - Transits at midnight
- 18 Dec
local mean time - Model vLSR range
- 0 to 0
km/s, flat rotation - LSR correction over a year
- −40 to +19
km/s at 40° N, 75° W
The anticentre is the least dramatic spectrum in the sky, and that is exactly why it is useful.
Why it is useful. Looking directly away from the Galactic centre, every circular orbit crosses your line of sight at right angles, so the model predicts zero radial velocity at every distance, the same as at l = 0°. Unlike the centre, there is no bar out here to break the model, so the real line is a single, fairly narrow peak close to zero. That gives you a known answer.
What to check with it. After the LSR correction, the peak should land within a few km/s of zero. If it lands at +30 or −25, the problem is in your pipeline, not the Galaxy. Typical culprits are a sign error in the correction, a wrong date or longitude, a tuner frequency offset you haven’t measured, or mixing the radio and optical velocity conventions. Fix it here and every other target gets better. The yearly swing below shows how much the raw, uncorrected peak moves through the year: at this declination it is one of the largest swings on this list, so a forgotten correction is obvious.
Practicalities. At +29° declination it rises well from both hemispheres; at 40° N it culminates near 79°. It transits at midnight in mid December, so it is a winter target for night observing in the north. The Crab Nebula (Taurus A) is about 7° away at l ≈ 185°, b ≈ −6°.
Radial velocity (LSR) of gas at each distance along l = 180°, b = 0°, if everything moved on circular orbits at 220 km/s. The line stops where the sightline leaves R = 20 kpc.
In frequency, that model range is 1420.406 to 1420.406 MHz in the LSR frame. Your receiver sees it shifted by the correction in the last box above, so leave a margin of about 0.2 MHz either side when you set the span.
How high it gets
Altitude at meridian transit and time above the horizon per sidereal day, for this pointing at a range of observer latitudes. Below about 20° the beam starts picking up ground, so the last column is the one to plan on.
| Latitude | Transit altitude | Above horizon | Above 20° |
|---|---|---|---|
| 60° N | 59° | 21.7 h | 13.3 h |
| 50° N | 69° | 17.4 h | 12.4 h |
| 40° N | 79° | 15.6 h | 11.6 h |
| 30° N | 89° | 14.4 h | 11.0 h |
| 20° N | 81° | 13.5 h | 10.3 h |
| 0° | 61° | 12.0 h | 8.9 h |
| 20° S | 41° | 10.4 h | 6.9 h |
| 35° S | 26° | 8.9 h | 4.0 h |
Transit time by month
Local mean time of meridian transit on the 1st of each month. That is clock time without daylight saving, corrected by four minutes for every degree you sit east or west of your time zone's central meridian. The tools do it for your exact site. The transit comes about four minutes earlier each day.
- Jan23:00
- Feb20:58
- Mar19:08
- Apr17:06
- May15:08
- Jun13:06
- Jul11:08
- Aug09:07
- Sep07:05
- Oct05:07
- Nov03:05
- Dec01:07
Read alongside
Coordinates, visibility, transit times and the LSR swing are computed for this page with the same code as our calculators. The velocity model is circular rotation on a flat curve with R₀ = 8.5 kpc and V₀ = 220 km/s (IAU 1985), the textbook first approximation. Real spectra depart from it, and the notes above say where. Found an error? Tell us.