TARGET 09 · l = 330°, b = 0° · Norma, along the Norma arm
Norma, l = 330°
The southern twin of l = 30°: a clean tangent point with a terminal velocity near −110 km/s, well separated from local gas. The rotation-curve pointing for the south.
- RA / Dec (J2000)
- 16h 04m 28s
−52.4° - Transits at midnight
- 24 May
local mean time - Model vLSR range
- −110 to +63
km/s, flat rotation - LSR correction over a year
- −24 to +27
km/s at 40° N, 75° W
Everything we say about l = 30° applies here with the signs flipped.
Why it works. l = 330° is the fourth-quadrant mirror of l = 30°. The tangent point is again at half the solar-circle radius, and the flat-curve model puts the terminal velocity near −110 km/s, exactly the negative of the l = 30° value. For the fourth quadrant the tangent-point method uses the low-velocity edge instead of the high one, and the sign of sin l takes care of the rest.
What you’ll see. A broad profile from about zero down to that negative edge, plus a positive tail from far-side gas beyond the solar circle, which the model extends to about +63 km/s at R = 20 kpc. The Norma arm runs through this direction.
Why it matters. Measuring both l = 30° and l = 330° is a good check on your velocity calibration. In a symmetric Galaxy the two terminal velocities would be equal and opposite. Real measurements are not perfectly symmetric, but if yours differ by tens of km/s, look at your LSR correction and frequency offset before you look for new astrophysics.
Practicalities. At −52° declination it is a southern target. It culminates at 73° from 35° S and at 8° from 30° N, which is effectively unusable. It transits at midnight in late May.
Radial velocity (LSR) of gas at each distance along l = 330°, 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 1420.106 to 1420.927 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 | never rises | 0 h | 0 h |
| 50° N | never rises | 0 h | 0 h |
| 40° N | never rises | 0 h | 0 h |
| 30° N | 8° | 5.5 h | 0 h |
| 20° N | 18° | 8.2 h | 0 h |
| 0° | 38° | 12.0 h | 7.4 h |
| 20° S | 58° | 15.7 h | 11.0 h |
| 35° S | 73° | 20.7 h | 13.7 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.
- Jan09:21
- Feb07:19
- Mar05:29
- Apr03:27
- May01:29
- Jun23:24
- Jul21:26
- Aug19:24
- Sep17:22
- Oct15:24
- Nov13:22
- Dec11:24
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.