The ‘star’ of the show this month is, of course, Saturn. Its 29.4 year rotational period around the Sun offering us a changing aspect of the rings each year with an edge on view every 15 years or so. We’ve recently had the rings open to their maximum extent giving good views of the Cassini division and other detail. So much so that Damian Peach and collaborators have produced the most amazing ground based image of Saturn this year. The next edge on view isn’t due until 2024 and so there’s still time to have a look at the rings in all their glory!
Saturn reached opposition in mid June and so this month continues to be good for seeing the planet in the south around midnight. It is low in the sky and so subject to atmospheric disturbance and dispersion. The superb image above was captured at a lower latitude and higher altitude and so the effects of the atmosphere were reduced. For Bath Astronomers, a good night’s seeing will give nice views in most instruments with the larger ones able to pick out large scale details in the rings and banding on the planet as it whizzes around every 10 or so hours.
The Cassini spacecraft has been orbiting Saturn for years beyond its original mission objectives and has continued to be the explorer that gave us astonishing data on the Saturnian weather, the rings, and the moons including the hydrocarbon seas of Titan and the potential for life on Enceladus. Now in its Grand Finale of 22 orbits between the planet and the ring system, July sees the commencement of the 12th orbit that plummets into the unknown gap which has so far turned out to be surprisingly empty of dust. Despite this absence, the antennae is still being used as a ‘bullet proof jacket’ by pointing it in the direction of travel rather than back at Earth during each flyby.
The final orbit will end on 15th September as Cassini enters the gas giant’s atmosphere. Pointing its antennae at Earth as long as it can maintain attitude, it will descend into the thickening atmosphere and continue its science mission to the last bit. Not designed for re-entry, Cassini’s structural integrity will fail and it will disintegrate, vaporise and become part of the Saturn atmosphere; a tiny dot of firey human ingenuity streaking across the face of Saturn, too small to be observed from afar except for the loss of signal over the deep space network at 12 noon on 15th Sept, about 1 hour 20 minutes after the loss of the craft.
Jupiter is still with us in the western skies after sunset for several hours. However the annual path of the Sun on the ecliptic is catching it up and it’s best viewing is over for the Summer/Autumn. That said it still looks spectacular with a subtly changing view each time you go to the eyepiece. If you have access to a larger scope, you may be able to make out some detail in the banding and see that from hour to hour, the disk is rotating slowly; once every 10 hours or so. In binoculars and smaller scopes, you can monitor the moons Io, Europa, Ganymede and Callisto orbiting with such short periods that you can detect change across a night’s observing or given current position, across several nights; Io has a period of just 1.77 days and Europa of 3.55 days. By the early hours, Jupiter will have descended below the horizon so it is the best option to start the night’s observing and is visible from sunset as it is not impacted by the lack of true darkness this time of year.
Still lost in the glare of the Sun, Mars will remain essentially hidden throughout July.
Venus is improving as, although its greatest elongation was in early June, the phase is improving to give us maximum brilliance by mid July visible in the morning sky a couple of hours before dawn in the north east.
Mercury is approaching greatest eastern elongation at the July and will be well placed given a good north western view for around 30 minutes after sunset.
Despite the lighter skies this time of year, both Uranus and Neptune are available in the morning skies through July although you’ll require a telescope and a good finding guide/software for the day you are trying to find them.
This month the Full Moon is on 9th July and the New Moon is on 23rd July. Follow the Moon night by night to see how the shadows change falling across craters, mountains and rilles. Also the track of the Moon will pass the planets in turn and offer different perspectives which could spark interest in amateur photographers.
If it is Messier objects you are after then the one overhead this time of year is M13 in Hercules. The best globular cluster in northern skies. It is also easy to find. Similarly the nearby M57 Ring Nebula in Lyra gives a wonderful example of this stellar phenomenon. The sky to the south is rich with objects this time of year as can be seen from the yellow markers in the image above and although the relative darkness makes some harder to find, they are certainly worth the effort. Have a look at the web site’s Planisphere to find out more.