On Monday 18 June the Moon will occult brilliant Venus, mag -4.4, at about 13:58 UT). The exact time of the occultation will depend on your location – the further West you are, the earlier it will occur, so be prepared up to 5 minutes before these times. The occultation is visible from SW Asia, Northeastern North America and Europe.
The Moon will be a thin crescent, 14.4% illuminated, so it won’t be all that easy to see in the bright noontime sky. Venus will lie almost directly in the Moon’s path, so once you see it, bisect the angle of the ‘horns’ and look for Venus ahead of where the front of the full moon’s disc would be.
In fact, it might be just as easy to see Venus first: at 13:30 UT it will be at R.A. 08h 59m 50s; Dec. +18° 57′ 16″. It’s altitude in the sky will depend on your location. If you find it, the Moon will lie to the right and slightly above it.
Another way to try to locate it is to set your telescope up at about 10:30 UT, and locate the Sun, being careful not to look directly at it, and certainly DO NOT look through the telescope at it, UNLESS YOU HAVE A PROPER SOLAR FILTER! See any astronomy observing book or check the web if you are not sure how to do it.
What you are aiming to do is aim your ‘scope to a point in the sky where Venus & the Moon will be just before the occultation. For this purpose, roughly at 13:40 UT, about 10-20 minutes before the occultation, to allow you to select your best eyepiece, or attach your camera etc, before the event begins.
Use the declination circles (or GOTO controls) on your scope to position it if it has them, or check the night before how many turns of the declination slow motion handle move it through that amount. Note that declination is not the same as altitude, but in this case it should be close enough to get the Moon in the field of a wide field eyepiece, and it will give you an extra minute or two location time.
Leave the telescope locked in this position, and at about 13:40 the Moon & Venus should appear in the field of view of a widefield eyepiece.
Then unlock the clamps, and follow Venus as it moves due to earth’s diurnal rotation, until the occultation starts. The visible occultation will take just under a minute to occur – obviously you will only see the occultation of the visible part of Venus’ disc! Venus will be 44% illuminated, so it will appear just under ‘half’ phase. The Southern tip of Venus’ thick crescent will be the last to disappear.
Venus will reappear from behind the Moon’s bright trailing limb at about 15:19 UT.
Ephemeris information for the occultation can be found at: http://www.lunar-occultations.com/iota/planets/0618venus.htm
Graphics:
Disappearance of Venus
Reappearance of Venus
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