Jul 10

Sky Report: July 11-17

The moon is full on Wednesday, July 13, at precisely 12:38:26 p.m. MDT. How long is the moon full? Just for that one instant. It’s full for as long as it’s midnight, or any other time – just for that moment. In practice we say the moon is full for that entire night. But what do we think when the moon is full at approximately noon, as it is this month? Is it full the entire day that began at midnight on the morning of the 13th and ends at the following midnight? Or is it full from the afternoon of the 13th until the following afternoon? It’s up to you. Generally you can consider it full on that one calendar day.

But what about other time zones? If it’s full at, say, 12:30 a.m. in the Mountain Time Zone, it’s full at 11:30 p.m. on the day before in the Pacific Time Zone. This is true for any astronomical event that happens at only one moment; it happens at a different time in each time zone and at different days where the time zone changes at midnight from one day to the next. It’s a consequence of living on a globe and astronomers have learned to live with it, but it can cause confusion. When looking up dates of full moons in a table, for example, you need to know which time zone the table was prepared for.

So where is the moon when it’s full on the evening of the 13th? It’s quite low, in the middle of Sagittarius, the Centaur/Archer, a composite beast that is half man and half horse (the front half is the man!). Being opposite the sun – which is what a full moon is – it rises at sunset and is above the horizon the entire night. Sagittarius is in the direction of the center of the Milky Way, and that is the brightest part of the Milky Way, but you won’t see the Milky Way because the moon’s bright light washes it out. Look next week when the moon is out of the way, and perhaps I’ll have more on that then.

On the 13th, 40° to the left of the moon, is the planet Saturn, shining as bright as the brightest stars. On the 15th and 16th the moon is much closer to Saturn, passing closest to it at about 2 p.m. on the afternoon of the 15th, and if you were on the opposite side of the earth you’d enjoy a very close conjunction.

Jupiter is another 40-some degrees to the left of Saturn, and it’s brighter than any star. It rises around midnight, and it rises a half-hour earlier each week – as do all the planets except Venus.

Mars is 30° to the left of Jupiter. Mars is the same brightness as Saturn.

Last but far from least is Venus, which rises 2 hours before the sun and which is low, but brilliant, in the east-northeast in morning twilight.

Stellar Vista Observatory provides portable telescopes and tripod mounted binocular kits on loan for free to residents and visitors in Kane County. Enhance your enjoyment of the night sky! For details or to request a loan, visit https://stellarvistaobservatory.org/discover-the-night-sky/ or drop in to the Kane County Office of Tourism.

The Sky Report is presented as a public service by the Stellar Vista Observatory, a nonprofit organization based in Kanab, Utah, which provides opportunities for people to observe, appreciate, and comprehend our starry night sky. Additional information is at www.stellarvistaobservatory.org. Send questions and comments to John@StargazingAdventures.org.

About the Author:

John Mosley was Program Supervisor of the Griffith Observatory in Los Angeles for 27 years and is the author of “Stargazing for Beginners” and “Stargazing with Binoculars and Telescopes”. He and his wife live in St. George where he continues to stargaze from his retirement home while serving on the advisory committee for Stellar Vista Observatory.

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