news sciences: What’s special about this full moon?

This morning’s almost full moon – April 10, 2017 at 4:15 a.m. – from Deirdre Horan in Dublin.

Full moon comes on April 11, 2017 at 06:08 UTC; translate to your timezone). For time zones in the Americas, the fullest moon will come on the night of April 10.

This full moon is the 1st full moon of northern spring – that is, the first full moon following the March equinox. As such, it fixes the date of Easter Sunday. By ecclesiastical rules, Easter falls on the 1st Sunday after the 1st full moon in a Northern Hemisphere spring. That means the earliest possible date for Easter is March 22, and the latest possible is April 25.

Skylore assigns names for every full moon. The April full moon is called the Grass Moon, Egg Moon or Pink Moon here in the Northern Hemisphere. In the Southern Hemisphere, where it’s autumn now, this full moon is the Hunter’s Moon, or full moon following the Harvest Moon (which is the full moon nearest to – not necessarily following – the equinox).

The April 10-11 full moon is special for another reason. It’s near Jupiter in the night sky. And Jupiter is special now because it’s only a few days past its April 7 opposition, when we passed between this giant planet and the sun. Jupiter was closest on April 8, that is, closest to Earth for all of 2017. So Jupiter is at its brightest and best now, and near tonight’s full moon.

Why does Jupiter appear near this full moon? Around the time we pass between an outer planet and the sun – and again that was just last week, for Jupiter – that planet appears opposite the sun in our sky. A full moon is also opposite the sun. So planets near their oppositions always appear – at some time within a month or so – near a full moon.

As the moon travels in front of the constellation Virgo on April 9, 10 and 11, it passes the king planet Jupiter and Spica, Virgo’s brightest star. Read more.

A full moon is always opposite the sun. That’s why it looks full to us. At full moon, the moon and sun are on a line, with Earth in between. It’s as though Earth is the fulcrum of a seesaw, and the moon and sun are sitting on either end of the seesaw. So as the sun sets in the west, the full moon rises. When the sun is below our feet at midnight, the full moon is highest in the sky. When the sun rises again at dawn, the full moon is setting.

At full moon, we’re seeing all of the moon’s day side. That’s why a full moon looks full.

In many ways, a full moon is the opposite of a new moon. At both the new and full phases, the moon is on a line with the Earth and sun. At new moon, the moon is in the middle position along the line. At full moon, Earth is in the middle.

Full moon always comes about two weeks after new moon, when the moon is midway around in its orbit of Earth, as measured from one new moon to the next.

Over the past several nights, the moon has been moving toward the brightest planet up each evening now, Jupiter. Here they are from Hong Kong on April 7, 2017, via our friend Matthew Chin. Read more: Full moon near Jupiter.

As the moon orbits Earth, it changes phase in an orderly way. Follow these links to understand the various phases of the moon.

Four keys to understanding moon phases

Where’s the moon? Waxing crescent
Where’s the moon? First quarter
Where’s the moon? Waxing gibbous
What’s special about a full moon?
Where’s the moon? Waning gibbous
Where’s the moon? Last quarter
Where’s the moon? Waning crescent
Where’s the moon? New phase

Bottom line: A full moon looks full because it’s opposite Earth from the sun, showing us its fully lighted hemisphere or day side.

Can you tell me the full moon names?

Moon in 2017: Phases, cycles, eclipses, supermoons and more