Venus encounters the moon before dawn

Before sunrise this Friday, October 9, Venus will briefly hide behind the moon, as seen from central and eastern Australia. This rare event is known as a Lunar Occultation of Venus.

For about an hour, the moon will travel past Venus blocking it from view. During this time, the moon will be found low to the eastern horizon.

People across eastern Australia will see the moment when Venus disappears from sight. It occurs about an hour before local sunrise, and Venus will be seen to disappear behind the moon’s bright crescent.

However, by the time Venus reappears near the dark edge of the moon, the sun will have risen and brightened up the sky. It so happens, that Venus is bright enough to be seen in the daytime, the tricky thing is knowing precisely where to look.

Since we know where Venus will reappear, it’s worth a try to see it. Binoculars will certainly make things easier, but be very careful not to point them anywhere near the sun.

Those in central Australia will not be able to see Venus disappear behind the moon, as the moon and Venus will be below the horizon at that time. But they will be able to see Venus reappear before the sun rises and while the sky is still dark.

The occultation won’t be visible from Western Australia. However, Venus will be found very close to the crescent moon.

And just a note of caution – David Herald’s fantastic Occult program, which I used to determine the timings of this event, gives a time for when Venus will disappear behind the moon as seen from Adelaide. However, it occurs when the moon is at a very low altitude, just 3 degrees above the horizon, so it’s most likely rather impractical to view it.

What will I miss if I sleep in?

The crescent moon can often be seen near Venus in either the early evening or early morning sky, and it’s generally quite eye-catching. Lunar occultations of Venus can happen between one and four times a year – as viewed from any location around the world.

What makes this event rare for us, is that it’s visible from much of Australia, and even more importantly, it mainly occurs during the hours before dawn.

Venus emerges from behind the moon, as seen from Broadstairs, England on June 19, 2007.Mark Kilner/flickr

Over the next 50 years, there are a handful of lunar occultations of Venus that are visible from Australia but they all occur during daytime hours. This is a rare opportunity to see Venus either disappear behind the moon or emerge from it against a dark sky.

With a telescope, it’s possible to see that Venus exhibits phases, just like the moon. But it takes 548 days for Venus to cycle through a full set of phases and during this time its apparent size varies as a result of its changing distance from Earth.

The changing phases of Venus as seen in the lead up to the Transit of Venus, June 8, 2004.Statis Kalyvas/VT-2004 programme

At the present time Venus is 40% illuminated, so the occultation is also a great opportunity to photograph the Moon and Venus together in their crescent phase.

What else is there to see?

Venus is not the only planet currently visible before dawn. Mars and Jupiter can also be seen, and on Saturday morning, October 10, the crescent moon will sit between them.

Venus, Mars and Jupiter can be found together in the eastern sky throughout October.Museum Victoria/Stellarium

Throughout the month, you can watch the dance of Venus, Mars and Jupiter as they change positions in the sky. Venus will move away from the bright star Regulus and travel towards Mars and Jupiter. Jupiter will drift higher in the sky, moving past Mars on the morning of October 18, and a week later it’ll be found paired up with Venus.

So for everyone who is up and about early in the morning, October is a great month to cast your eyes to the sky.