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View Full Version : Moon Occults Lam Gem - Eve May 21



Centaur
2015-May-21, 02:23 PM
The 17% illuminated waxing crescent Moon will occult (cover) the magnitude +3.6 star Lambda Geminorum for observers in North America during Thursday 2015 MAY 21. This will be an evening event in the eastern half of the continent including Chicagoland, and an afternoon event in the west.

Immersion will occur on the lunar dark limb and emersion on the bright limb. Observers on a graze path will witness the star winking on and off as lunar hills and valleys pass by. Observers between the two graze paths will see a full occultation.

I’ve created a North American graze map, preview graphic with data for Chicago, and a set of Besselian elements. They can be seen at www.CurtRenz.com/occultations.html

Photos and descriptions of the event would be welcome additions to this thread. If you would like specific occultation timing predictions for your location, please reply to this post with your longitude, latitude, elevation and time zone.

chornedsnorkack
2015-May-21, 08:40 PM
Today, I was struck at where Venus was!
Having found the new Moon in evening sky, I started looking for Venus along ecliptic - on the line from Moon to Sun under the horizon. In vain.
And suddenly discovered Venus in a completely unexpected place. High above Moon.
How far is Moon passing Venus? And how far can Moon ever pass Venus?

Centaur
2015-May-21, 10:46 PM
Today, I was struck at where Venus was!
Having found the new Moon in evening sky, I started looking for Venus along ecliptic - on the line from Moon to Sun under the horizon. In vain.
And suddenly discovered Venus in a completely unexpected place. High above Moon.
How far is Moon passing Venus? And how far can Moon ever pass Venus?

That’s an astute observation. As viewed from Chicago during midday today, the Moon appeared to pass closest to Venus by 8.3. At the current moment as seen from Chicago, the Moon is 5.5 south of the ecliptic, which is near the maximum, and Venus is 2.8 north of the ecliptic but far from the maximum of 8.7.

In an extreme case the Moon can appear to pass Venus at an angular distance of over 14, but that would be during a period when both are nearly in conjunction with the Sun, and other factors happen to be in sync. Particularly in the case of the Moon, the parallax effect is significant and depends upon an observer's place on Earth. It can result in the Moon appearing up to 1 (2 lunar diameters) from its predicted geocentric position.