Right Ascension Converter

Switch sky coordinates between hours and degrees.

What it does

Telescopes list east west sky positions in hours, maps use degrees. Earth turns 360 degrees in 24 sidereal hours, so one hour is fifteen degrees. Converting is scale only, no offsets.

The tool above switches hours and degrees. The defaults convert 6 hours, so the page opens showing 90 deg. Pick new units to update the result.

Hours to degrees multiplies by 15. Degrees to hours divides by 15. Six hours gives ninety degrees, a quarter turn. Ninety degrees back gives six hours.

Use hours for catalogs and mounts, degrees for plots and separations. Minutes and seconds of RA subdivide hours by 60, not degrees directly.

This page shows the factor, one full hand checked example at 6 h, a reference table, and practice checks that run through the tool.

How to use

1. Type the coordinate number.
2. Pick hours or degrees as start.
3. Pick the other as target.
4. Read the main result.
5. Keep hours below 24, degrees below 360.
6. For RA minutes divide hours first.

Formula

h

Right ascension hours 0 to below 24.

deg

Degrees 0 to below 360.

15

Degrees per hour.

Same units must differ here. Ranges wrap, negatives rejected in this simple form.

Worked example

Reference table

Limits

• Hours and degrees only. No minutes/seconds split here.
• Ranges 0-24 and 0-360 enforced.
• Sphere math ignored. Separations need spherical trig.
• Precession ignored.

Common mistakes

• Using 60x instead of 15x.
• Mixing RA minutes with arcminutes.
• Entering 24 h or 360 deg at the wrap.
• Adding offsets like temperature.
• Reading hours as clock time.

Try it yourself

Quick checks. Answers sit tucked under each question.

Questions

Sources

• BIPM: SI Brochure
• NASA: Year Dating Conventions

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