July Night Sky

July is another bright sky month, so not so good for nebulae and galaxies, but not a problem for the brighter planets, and sometimes it seems to be easier to pick up detail on them in these conditions.

This is probably the best time this year to see Saturn. It can be seen very low in the south as darkness falls after 10pm – I provided a map in my May posting, but it should not be hard to find as it is the brightest object in that part of the sky.

Saturn has something to offer at all levels of optical equipment. Try looking at it with the naked eye. Like all planets, it shines with a steady light because the size of its disc (even if you can’t see it as such) balances out the natural fluctuations in the earth’s atmosphere that makes stars twinkle. But most planets are either too bright (Venus, Jupiter)  or too faint (Uranus, Neptune) for this effect to be very apparent. Saturn is about the same brightness as the brighter stars in the sky (such as Arcturus and Vega), but the steadiness of its yellow light is very distinctive, almost baleful. It is not hard to see why some of the ancients identified it with a very ancient god.

Now try looking at it with a pair of binoculars. It is immediately apparent that its shape is odd, rather like a rugby football suspended in the sky; the exact appearance will depend on the type of binoculars, but any  will show this oddness of shape.

A telescope will reveal the famous rings. They are very open in this apparition, so it is a good time from that point of view to look for detail. The easiest to see is Cassini’s division, a black arc in the outer part of each end of the rings as we see them. There are more details of shading in the rings, but their visibility will depend on seeing conditions. Saturn’s north pole is titled towards us (it is their summer, too!), so you can see the northern part of the rings disappear behind Saturns’s disc, and you may be able to see the planet’s shadow on a section of the eastern part of the rings as they disappear behind the disc. If you now turn to the southern part of the rings as they pass in front of the disc, you may be able to see the disc through some parts of the ring.

The disc itself may offer detail, but normally has less to offer than Jupiter in this respect.

Finally, Saturn’s moon collection is second only to Jupiter’s. The largest, Titan, will generally be visible, appearing like a nearby 8th magnitude star. A good telescope will show 3 more of about 10th magnitude.