Finding the planets

This page contains links to (what will be) 10 separate databases for planetary positions from 2001 - 2005 inclusive, for both Northern and Southern Hemisphere observers. Initially, only the Southern Hemisphere database for 2001 is available (they are a LOT of work !!). [I anticipate completion in March 2001.]

Following the table of links is a description of

• how they were created, and
• how they can be used.

Calculation of Right Ascention and Declination

These were computed on a weekly basis using the US Naval Observatory's Multi-Year Interactive Computer Almanac (a DOS program).

All values are astrometric and geocentric (i.e., as if viewing from the centre of the earth) -- one can customise for a particular location if desired (but not necessary for our purposes). I did not do this, as the errors are very small indeed. Click here for more info.

Distance from earth, apparent size, and magnitude

These were also computed using the US Naval Observatory's Multi-Year Interactive Computer Almanac.

Distance from earth is in A.U. (astronomical units), which is the average distance between the earth and the sun.(approx. 150 million km).

If you are not familiar with the magnitude (brightness) scale, click here.

Apparent size is in minutes and seconds of arc [60 seconds = 1 minute]. From earth, the sun and moon appear to be approx. 30 minutes of arc. Therefore Venus (at its nearest approach to earth) reaches 64 seconds of arc -- about 1/28 the apparent diameter of the full moon. Mars (at its closest approach to us) reaches 25 seconds of arc -- about 1/72 the apparent diameter of the moon.

A useful exercise for students is to select a date (from one of the databases), and then draw the apparent sizes of all planets (and the sun) to the same scale. An Australian 20 cent coin (or American quarter) is a good size for the sun or moon (30 minutes). If you are observing at 80 x magnification, everything will appear 80 times larger...

The most interesting planets for observation with small instruments are Venus, Jupiter and Saturn. Mars is interesting when it's close-by. Mercury, Uranus and Neptune are easily seen with binoculars or small telescopes but aren't very spectacular. Pluto requires a telescope with an aperture of at least 8 inches.

Observing notes

I have been observing all of the planets for a long time, with binoculars, and home-made 3 inch (and 6 inch, and 13 inch) Newtonian reflectors, and the 18 inch Clark refractor at Amherst College. During late 2000, I observed all (including Pluto) from Western Australian using an 8 inch Cassegrain.

Southern Hemisphere rise and set times are for Perth, Western Australia, but will be accurate to within about 30 minutes for any mid-latitude location in the Southern Hemisphere. The Northern Hemisphere tables use Washington, D.C. as the reference point, but will be accurate to within about 30 minutes for any mid-latitude location in the Northern Hemisphere. All times are standard time, NOT daylight savings time.

I have assumed a horizon obstruction of about 15 degrees when estimating rise and set times. Even if you have a good horizon, images will be blurry when the planets are that close to the horizon. For Pluto, I recommend trying to find it ONLY when it's at least 30 - 40 degrees above the horizon.

The position of every planet, on a weekly basis, was determined using the Starry Night planetarium program. [It's time consuming !] Several "inserts" of interesting planetary alignments were also made by taking screen shots from Starry Night.

Tips on using the tables

I've included the sun's coordinates as a reference point. Since most solar system bodies lie in the ecliptic (excluding comets and some asteroids), and since right ascention (RA) is a TIME measurement, you can subtract the planet's RA from the sun's RA, and get a good approximation of how many HOURS it precedes or follows the sun. This gives you an approximate location without using star maps -- and works well for the brighter planets.

For example:

On 1 January 2001, the sun is at 18 hours 50 minutes, and Venus is at 22 hours 5 minutes. This means Venus will set approx. 3 hours after sunset. On the same date, Uranus is at 21 hours 25 minutes; it will rise about 2 1/2 hours before sunrise.

For much more accurate positioning, plot the planets' locations on the star maps provided.

Happy observing !

Written by Stephen R. Kessell
Updated 8 February, 2001