Observations

Saturn hides behind the Moon in 2019

Saturn reappears from behind Moon during occultation of 2014 August 04
Saturn peeks out from behind the Moon. A screenshot from Sydney Observatory’s live stream of the occultation of Saturn, 04 August 2014. The Moon is overexposed in order to see Saturn clearly.

During 2019 a series of lunar occultations of Saturn occur. During these occultations the Moon moves in front of and covers, or occults, the more distant planet Saturn. This happens almost monthly this year although from any single location only a few occultations are visible.

Australia has several chances to witness these occultations of Saturn in 2019. The best opportunity for the eastern states comes in the evening of August 12. On May 23 there is a poor, and very challenging to observe, daytime occultation and the far north and west of Australia (Darwin and Perth regions) see another on September 8-9. The first of the 2019 occultations that is worth viewing will occur on April 25-26.

What will I see on April 25-26?

The Moon rises late in the evening on April 25, ANZAC day. This occultation is visible from south and east of a line joining (roughly) Cairns to the Bight. However, only those south and east of a line joining (roughly) Brisbane to Mount Gambier will see the whole event. From many locations the Moon will already have moved in front of Saturn before it rises so the disappearance of the planet will not be seen.

As the Moon rises look carefully at its lower-right edge to see a ‘star’ – this is Saturn. Binoculars or a telescope will assist greatly! Within an hour or so of moonrise the Moon will have moved far enough on its orbit around the Earth to reveal Saturn. This occurs against the dark limb of Saturn so will be far easier to see. The planet’s reappearance occurs near the top-left edge of the Moon.

This particular occultation is not ideal. The Moon is very close to the horizon and just rising. You will need a clear view towards the east with no low cloud. Binoculars or a telescope will help you find Saturn.

The Moon showing locations of Saturn's disappearance and reappearance on the limb during the occultation of 25-26 April 2019
The points of disappearance and reappearance of Saturn on the Moon’s limb during the occultation of April 25-26, 2019, as seen from Sydney. Other locations will see a similar situation. From the 2019 Australasian Sky Guide by Dr Nick Lomb, copyright MAAS.

During a previous occultation of Saturn, on 04 August 2014, Sydney Observatory live streamed the event. This gives you some idea of what to expect. In particular, the Moon is much brighter than Saturn making viewing this with the naked eye challenging. Binoculars or telescopes are recommended.

At what time does the occultation happen?

From Sydney the Moon rises at 10:03pm (all times here are Sydney times in AEST) with Saturn rising just 3-minutes later. Saturn may just be visible to the bottom-right of the Moon. While the Moon and Saturn are both rising up and away from the horizon (due to Earth’s spin on its own axis) the Moon is also moving slowly back down towards the eastern horizon (due to its own orbital motion around the Earth). At 10:30pm the Moon moves in front of Saturn – the occultation begins. You will notice the Moon has almost reached last quarter phase so it is slightly more than half-illuminated. Saturn disappears against the bright limb of the Moon. At 11:25pm Saturn reappears at the top-left of the Moon. The reappearance should be more noticable for being against the dark limb of the Moon. For other locations the pattern of events is much the same but please see Astroblogger’s predictions for local times.

Where can I see this from?

The following chart shows which parts of Australia and New Zealand will see the lunar occultation of Saturn on April 25-26, 2019.

A world map showing the region where the April 25-26 lunar occultation of Saturn is visible
The April 25-26, 2019 occultation of Saturn is visible from the south-eastern part of Australia and New Zealand. If you live between the white lines you can see the full occultation during nighttime. If you live within the cyan elipsoid Saturn is already behind the Moon at moonrise . Map courtesy of Occult4 software by Dave Herald.

How can I best observe this?

While these occultations can be observed with just the naked eye, they are best seen with binoculars (set on a stand or resting solid surface) or a telescope. The contrast in brightness between the (bright) Moon and (fainter) Saturn makes naked eye viewing challenging. Additionally, the Moon being very close to the horizon makes this one particularly difficult to observe.

When is the next one?

On August 12 there is a much easier occultation to view. It occurs in the early evening and will be easily seen high in the eastern sky. We will provide more details closer to the date. If you found this occultation difficult to observe or if you were clouded set aside the evening of August 12, 2019 for the next Saturn occultation.

 

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