July's Full Moon Rises Sunday With 'Sea Goat'

The traditional names for the full moons throughout the year can be strange and almost exotic to city dwellers, but they make sense to people living in rural areas. Just take July's full moon, known as the Hay Moon.

The Hay full moon, which occurs Sunday in the constellation Capricornus (the Sea Goat), comes as no surprise to anyone living on a farm that may have spent recent weeks cutting, baling and stowing hay for the winter. The moon will be at its fullest Sunday night at 9:36 p.m. EDT (0136 GMT).

(This graphic shows how July's full moon will appear on Sunday, July 25.)

The full moon itself is an instantaneous event, when Sun, Earth, and moon fall in a straight line. To the naked eye, the moon looks full for at least a day on either side of that time, though eagle-eye skywatchers using a telescope can see a terminator ? a border between the lit and unlit portions of the moon ?  with shadowed craters somewhere around the limb of the moon.

By 1 a.m. EDT the moon will be close to the meridian, the north-south line passing through the zenith, and will be at its highest point in the sky for the night. [How Moon Phases Work]

Moon Hay, bucks and thunder

Like every full moon, July's full moon has more than one name associated with it. While farmers know it as the Hay Moon, the native peoples of northeastern North America didn't cultivate hay, so they associated this moon with bucks ? male deer.

Others call this the thunder moon, because this is the time of year when sudden thunderstorms are a frequent feature of hot summer afternoons.

Various peoples around the world have given special names to the full moons throughout the year, a simple way of recognizing the passage of time. The best known of these moon names are typically those used in the English language, but other well known naming systems are used by the Algonquian peoples of northeastern North America, the Hindus of India, and the widespread Buddhist religion.

Sea goat and the moon

This month full moon occurs with the moon in the constellation Capricornus, the Sea Goat. This strange creature is half-goat and half-fish.

Less imaginative astronomers see this constellation as an upside-down triangle with the apex pointing towards the horizon, or as a three-cornered hat. Because none of its stars is brighter than third magnitude, Capricornus requires a fairly dark sky to be visible.

The upper right corner of the Capricornus triangle is marked by two interesting stars, both of which are wide double stars.

Algedi, sometimes known as Al Giedi (Arabic for "the goat"), can be seen as double by anyone with sharp vision. It is an optical double star, meaning that the stars are not in orbit around each other, but only appear double because they are in the same direction from the Sun.

Each component can also be seen to be double in a small telescope. Alpha-1 is 687 light years distant while Alpha-2 is only 109 light-years away; both are similar to our Sun in color.

Dabih (Arabic for "butcher"), the other star in the right corner, requires binoculars to split. It is a beautiful triple star located 345 light-years from the Sun. Its three components can be separated in binoculars. It shows a fine color contrast with two yellow stars and one blue star.

The left corner of the triangle is the 3rd magnitude star Deneb Algedi (Arabic for "the goat's tail") and the bottom corner by the 4th magnitude Omega Capricorni.

Magnitude is a measure of the brightness of stars and other celestial objects in which the smaller the number, the brighter the object. Negative numbers are the brightest. The scale assumes dark skies.

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