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Moon, Mars, star Spica on July 5, with Saturn nearby


Tonight for July 5, 2014

Look for a wonderful sky scene as soon as darkness falls on July 5, 2014. That star shining in the glare of the moon is Spica, the brightest star in the constellation Virgo the Maiden. Plus, the slightly brighter starlike object near the July 5 moon is actually no star at all. It’s the red planet Mars. If you’re in Central America and South America on the night of July 5, you might actually see the first quarter moon cover Mars, in an event that astronomers call an occultation. More about the occultation below.

But first, a lesson in identifying planets. The planets in our solar system orbit the sun in a nearly flat plane. That means they move across our sky not randomly, but along an well-defined path, the same path followed by the sun during the day. This path is called the ecliptic, and we’ve depicted it on the chart below.

The moon also moves on the ecliptic. That’s because Earth lies in the same flat space around the sun as the other planets. That line across the chart below really represents a projection of the Earth’s orbital plane onto the great dome of stars. Because the moon revolves around the Earth on nearly the same plane that the Earth revolves around the sun, practiced sky watchers know the moon is always found on or near the ecliptic.

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Over the new few days watch the moon move away from Spica and Mars and toward Saturn.

The moon and planets move across our sky on a well-defined path, called the ecliptic. Over the new few days, watch the moon move along this path, away from the planet Mars and star Spica, and toward the planet Saturn. As it does so, the moon will pass through a celestial gateway on July 6.

Occultation of Mars on July 5, 2014. As seen from the much of North America on July 5, the moon will shine in between Mars and Spica at nightfall. But if you’re at just the right spot in Central America and South America, you might even be able watch the moon occult – cover over – the planet Mars tonight. Click here for details on the July 5-6 lunar occultation of Mars.

If you’re using the occultation page to observe this occultation, remember you will need to convert the occultation times on that page from Universal Time (UT) to your local time. Click here to learn to translate from Universal Time. For instance, as viewed from La Paz, Bolivia, the moon occults Spica on July 6 from 2:36:37 to 3:34:34 Universal Time. However, people in Bolivia must subtract 4 hours from UT to convert to their local time. That means, as viewed from La Paz, the occultation takes place on July 5 from 10:36:37 p.m. to 11:34:34 p.m. Bolivia Time

The moon always travels eastward relative to the backdrop stars. So if you’re in the right place to witness the July 5 lunar occultation of Mars, this planet will disappear behind the nighttime side of the moon and reappear on the moon’s daylight side. That’s good! It’s lots easier to see a planet disappear along the darkened limb of the moon, than along the bright limb.

In a different kind of occultation, telescopes at different locations observed the dwarf planet Eris occult (cover over) a faint star in November 2012, enabling astronomers to accurately measure Eris’ size. Click here for a larger view. Image credit: ESO

The night side of a waxing moon always points eastward – or in the same direction that the moon travels in front of the constellations of the Zodiac. The eastward motion of the moon across our sky is carrying it toward another planet. Look for the moon to be closer to Saturn on July 6, and right next to Saturn on July 7.

Bottom line: Great sky scene on July 5! The moon is near the bright star Spica and the red planet Mars. If you’re in Central America and South America on the night of July 5, you might actually see this first quarter moon cover Mars, in an event that astronomers call an occultation.

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