You may find details of the month's planetary peregrinations in the curret issue of Astronomy Now magazine. Click here to find out more. Alternatively, to keep abreast of what's happening in the skies over the British Isles, including timings of bright lunar occultations, please consult our Night Sky page as well as the interactive Solar System data table below.

Jupiter's moons

With just a small telescope, you can observe the phenomena of Jupiter's moons as they transit Jupiter. You will also see them slip into Jupiter's shadow, or reappear from occultation at the opposite limb of the planet. This is a fascinating activity, and our pop-up interactive Jupiter program will enable you to identify Io, Europa, Ganymede and Callisto, get predictions of their shadow transits, and see how they move. You can also get timings of when Jupiter's Great Red Spot is visible with this versatile routine. You can also find details of the locations and transit times of the Galilean satellites every month in Astronomy Now magazine.


Interactive Solar System data table

For those requiring accurate observational data for the major bodies of the Solar System, we present a fully-interactive ephemeris that will appear in a pop-up window. With this very handy tool you will be able to plan your observing sessions.

Not only will you be able to see at a glance when and where the Sun, Moon and planets will be at any given instant, but deep-sky enthusiasts will be able to see when skies will be totally dark (when the Sun's altitude is below -18°) or devoid of moonlight.

Click the logo to launch Astronomy Now's interactive Solar System ephemeris in a separate window.

The table opens with information computed for the current date and Universal Time (essentially the same as Greenwich Mean Time). This is based on your computer's internal clock and time-zone localisation, so please make sure these settings are applied correctly on your machine. The localisation is initially set to the centre of the British Isles.

Changing the date and time entries and pressing the "Calc" button will recompute the table for the given instant. If you wish to return to the present date and time, press the "Reset" button. By using the other time buttons you may step forward or backwards by weekly, daily, hourly, or ten minute increments.

Since the program performs all its calculations in Universal Time, remember to add one hour to events generated by the table to obtain the British Summer Time equivalent. Similarly, subtract an hour from local time before entering it in the box when BST is active. Pressing "Reset" will always recompute the table to the current value of UT.

The table can produce data for other locations in and around the British Isles, too. Use the pull-down menus to select a location nearest you (a gazetteer or large-scale Ordnance Survey map will give you latitude and longitude information), then press the "Calc" button. The program will remember your chosen location for the session.

With a little experimentation it is possible to quickly determine the rising and setting times of any given object. Refraction is taken into consideration, so the Sun and Moon rise or set when their centres are at an altitude of -0.3°; other objects in the table rise or set when their altitudes are zero.

As seen from the British Isles, the Sun, Moon and planets rise with azimuths (compass bearings relative to true north) between approximately northeast and southeast, and set with azimuths between southwest and northwest.

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