How does this calculate a planet's position?

It uses Keplerian orbital elements with secular rates for each planet and Earth, solves Kepler's equation for the eccentric anomaly, finds heliocentric positions, takes the geocentric vector to the planet, converts ecliptic to equatorial coordinates, then to local horizontal alt/az using the observer's location and sidereal time.

What do altitude and azimuth mean?

Altitude is the angle above the horizon, from 0 degrees at the horizon to 90 degrees at the zenith; negative means below the horizon and not visible. Azimuth is the compass bearing measured clockwise from north, so 90 degrees is east, 180 is south, and 270 is west.

How accurate is this calculator?

The truncated Keplerian model is accurate to roughly a few arcminutes for the inner planets and within about a tenth of a degree for the outer planets over the years around 2000 to 2050. That is far more than enough to point a telescope or plan a session, though it is not a precision ephemeris.

Why must I use UTC instead of local time?

Sidereal time and orbital positions are computed from a universal clock, so the tool needs UTC to be unambiguous across time zones and daylight saving. Convert your local civil time to UTC by adding or subtracting your zone offset before entering it.

Why is the altitude negative for the planet I want?

A negative altitude means the planet is below your horizon at that moment and cannot be seen. Try a different time of night, or check when it rises; planets near the sun in the sky may only be up briefly after sunset or before dawn.

Planet Altitude & Azimuth Calculator

Before hauling a telescope outside, it helps to know whether your target planet is even above the horizon and where to point. This calculator computes a planet’s altitude and azimuth from orbital mechanics for any time and place, so you can plan a session or slew a mount with confidence.

How it works

The computation chains together standard positional-astronomy steps:

Orbital elements for each planet and Earth are evaluated at the requested date using linear secular rates (semi-major axis, eccentricity, inclination, longitudes).
Kepler’s equation M = E - e * sin(E) is solved iteratively for the eccentric anomaly E, giving each body’s heliocentric position in its orbital plane.
Positions are rotated into heliocentric ecliptic coordinates, and the planet vector minus Earth’s vector gives the geocentric direction.
Ecliptic coordinates are rotated to equatorial (right ascension, declination) using the obliquity of the ecliptic.
Finally, the local hour angle from sidereal time and the observer’s latitude convert RA/Dec into altitude and azimuth.

Reading the result

An altitude above 0 degrees means the planet is up; higher is better, since objects near the zenith shine through less atmosphere. Azimuth tells you the compass direction to face: north is 0, east 90, south 180, west 270.

Tips

Enter the time in UTC — convert from your local clock first. The model is excellent for pointing and planning across the decades around the year 2000, accurate to a few arcminutes for the bright planets. For the best views, observe when the planet is highest, which for outer planets is near its meridian crossing around local midnight at opposition.