October 23, 2017

AstroEvent: 4x Planets, 1xMoon, and a 12° FOV!

Looking eastward May 1st about 30 minutes before sunrise. (Created by the Author using Starry Night).

Where have all the planets gone? Four of the five classical naked eye planets are about to reveal themselves this week in a splendid fashion. As Venus sinks morning by morning towards the horizon, expect Jupiter, Mars and Mercury to emerge low in the dawn sky. The action culminates the weekend of April 30th-May 1st, when the waning crescent Moon approaches the grouping… use brilliant Venus as a visual “anchor” to guide your eyes to the fainter planets. On what date will you be able to spot each planet from your location? Can you do the feat with binocs or the naked eye? How ‘bout attempting to see the planet Venus next to the daytime crescent Moon on April 30th? On what date will you be able to see that slimming crescent Moon one last time as it approaches New on May 3rd at 7:51UT? These are all fun feats of visual athletics to try in this coming week.

Also, a brief shout out for observers along a line from Virginia to Vancouver to be sure and catch the occultation of a +10.3 magnitude star by the asteroid 7 Iris in the early morning hours of April 30th…  good luck, and be sure and let us know of any tales and tribulations of said visual athletics!

The Astro-word for this week is Extreme Crescent. Around every New Moon, there is a sub-category of dedicated (some would say obsessed) observers who endeavor to break records attempting to spot the “oldest” or “youngest” lunar crescent. Like everything else, there’s a site for that which gives the particular circumstances and prospects for each lunation worldwide. These targets can be tough, as a hair thin crescent is in very low contrast to the bright twilight sky. This feat is also restricted by our friend, the Danjon Limit, which states that the feat approaches impossible as the angular separation between the Sun and moon reaches <7°… so why bother? Well, beyond the basis that the sighting on the New Moon has with certain calendar systems, such feats demonstrate what the physiology of the human eye is capable of. Our own bodies have surprised scientists before… and hey, it’s a more noble pursuit than collecting pay toilet tokens, right?

 

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