The four Galilean satellites of Jupiter are readily visible through a pair of binoculars or a small telescope.  A small telescope will also show at least Titan, the largest satellite of Saturn: a 20 cm telescope will show up to four other Saturnian satellites.

Eclipses of Saturn's satellites will be occurring during the next few years. Through small telescope only those of Rhea and Titan are likely to be observable. Those of Rhea started in 2008, Titan start in 2009

Artificial Earth satellites can be seen moving silently across the sky almost any clear night. Information on when and where to look is available.

---

Events of the Galilean Satellites of Jupiter Visible from New Zealand

Binoculars are sufficient to observe the 4 Galilean Satellites of Jupiter although a small telescope makes viewing easier. With a magnitude of about 5 they would be visible to the naked eye from a dark site if it were not for the glare of Jupiter. At regular intervals in its orbit round Jupiter, a satellite will be eclipsed in Jupiter's shadow, or occulted as it passes behind Jupiter or it will transit across the face of Jupiter. When any of these happen the satellite cannot be seen. Hence it is quite likely that at any time not all four will be visible.

Complete predictions of all events of the Jovian Satellites are available at the Institut de Mecanique Celeste at de Calcul Ephemerides.

Return to         Top of page       RASNZ home page.

---

Titan, Saturn's largest satellite

Titan, with a magnitude of about 8.5, can be seen through a small telescope. The satellite takes about 16 days to orbit Saturn. The table shows the dates of its extreme positions with respect to Saturn for 2009. Close to conjunction with the Sun, it is not possible to view planet, data is omitted for a few weeks either side of conjunction on September 18.

When at eastern or western elongation Titan's distance from the planet is about 5 times the diameter of the planet and its rings. During 2009 when north or south of Saturn, Titan is so close to Saturn that it will either transit across the face of the planet or pass behind the planet, so being occulted, by it. Eclipses of Titan, when it passes through Saturn's shadow also occur in 2009.

The table below shows the dates at which Titan is at eastern or western elongation and when it is north or south of the planet, which in 2009 means it will either transit the planet or be occulted by it. Transits occur about 4 days after eastern elongation, before September when Titan is to the north, after September when it is to the south. Occultations, and eclipses, occur about 4 days after western elongation, before September when Titan is to the south and after September when to the north.

The Earth passes through the ring-plane of Saturn on 4 September 2009. On that date the rings will appear edge on as seen from the Earth. Unfortunately Saturn is at conjunction with the Sun two weeks later, so will be very low in the evening twilight sky following sunset, making it very difficult to observe. The rings are edge on to the Sun earlier, on 10 August. Since 1995 when the rings were last edge on, the south pole of Saturn has been tilted towards the Earth and Sun, after becoming edge on this year, the north pole will be tilted towards us.

One result of this change over can be seen in the order of events in the orbit of Titan. Before September, Titan is to the north of Saturn after eastern elongation, after September it will be to the south. The plane of Titan's orbit, like all the larger satellites except Iapetus, is very close to the ring plane, hence the change when the orientation of the ring plane changes.

Titan, like most of the inner satellites of Saturn, orbits the planet in a plane close to the equator of Saturn and close to the plane of the rings. The equator and rings of Saturn are inclined at an angle of about 26° 45' to the plane of its orbit. This is just over 3° more than the inclination of the Earth's equator to its orbit.

For about half the time of its 29.5 year orbit of the Sun, the south pole of the planet is tilted towards the Sun, as at present. This is Saturn's equivalent to our summer in our southern hemisphere. At the same time the southern face of the ring system is lit by the Sun.

For the other half of the time the north pole is tilted towards the Sun, as in the southern hemisphere winter. The northern face of the ring system is also then lit. At the time of change over the equatorial rings become edge on to the Sun.

The rings become edge on to the Sun twice during Saturn's 29.5 year orbital period, following which the opposite face of the rings becomes lit. Also the Earth passes through the ring plane near the same time so that as seen from the from the Earth the rings appear edge on and for a short time difficult, if not impossible, to see. The Earth may in fact make either one or three passes through the ring plane over a period of a few months (never just two as in the end the face we can see changes).

Recently Saturn's rings have been closing as seen from the Earth. This will become very noticeable during 2008 so that by the end of the year they will look very narrow. After that they will in fact open slightly again during the first part of 2009 as the Earth swings round in its orbit, but the Earth will finally cross the ring plane on 2009 September 4 at 13:45 UT, (September 5, 1.45 am NZST, after Saturn has set in New Zealand). In 2009 there will be only 1 passage of the Earth through the ring plane.

The rings will be edge on to the Sun a few weeks earlier on August 10. After August 10 the northern face of the rings will be turned towards the Sun, while from Earth we will be seeing the southern, unlit face. This may make it difficult to see the rings during this time. They will in any case be nearly edge on from our point of view.

Eclipses of the inner satellites of Saturn only occur near the time the rings are edge on to the Sun. Of the somewhat brighter satellites, Mimas is closest to Saturn, its eclipses started in April 2006, Enceladus started in December 2006. Mimas and Enceladus need a moderate sized telescope to see at any time, the eclipses take place when the satellites appear close to Saturn making them even more difficult to see.

Tethys commenced eclipses 2007 August 27 and Dione 2007 December 26. Although these satellites are a little brighter and fairly easy to see in a 20 cm telescope, the eclipses also take place close to the disk of Saturn, so making them difficult targets.

Rhea will start being eclipsed mid 2008. Some of these eclipses will be further out from Saturn,also Rhea has a magnitude 9.8 making it a reasonably easy object, so eclipses may be detectable. Titan will be the easiest target, its eclipses start 2009 February 16. Titan has a magnitude 8.4 so is easily visible in a small telescope. Eclipses occur at 16 day's interval, each successive eclipse staring about an hour earlier. The first few again occur close to Saturn's disk, but a few in April and May particularly should be well placed for evening viewing from New Zealand.

Predictions for eclipses of Rhea and Titan are on this site.