Astronomy Picture of the Day
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2017 April 10
Explanation: Why would this cluster of galaxy punch a hole in the cosmic microwave background (CMB)? First, the famous CMB was created by cooling gas in the early universe and flies right through most gas and dust in the universe. It is all around us. Large clusters of galaxies have enough gravity to contain very hot gas — gas hot enough to up-scatter microwave photons into light of significantly higher energy, thereby creating a hole in CMB maps. This Sunyaev–Zel’dovich(SZ) effect has been used for decades to reveal new information about hot gas in clusters and even to help discover galaxy clusters in a simple yet uniform way. Pictured is the most detailed image yet obtained of the SZ effect, now using bothALMA to measure the CMB and the Hubble Space Telescope to measure the galaxies in the massive galaxy cluster RX J1347.5-1145. False-color blue depicts light from the CMB, while almost every yellow object is a galaxy. The shape of theSZ hole indicates not only that hot gas is present in this galaxy cluster, but also that it is distributed in a surprisingly uneven manner.
What’s special about this full moon?
Tonight’s full moon (April 11 at 6:08 UTC) is the 1st full moon of northern spring and fixes the date of Easter Sunday
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.
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.
Bottom line: A full moon looks full because it’s opposite Earth from the sun, showing us its fully lighted hemisphere or day side.
Deborah Byrd created the EarthSky radio series in 1991 and EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. “Being an EarthSky editor is like hosting a big global party for cool nature-lovers,” she says.
Published on EarthSky
The Wisdom of Buddha
The wise ones fashioned speech with their thought, sifting it as grain is sifted through a sieve.
Your Ancient Symbol Card for Today
Altruism denotes the noble act of giving to those in need without the expectation of a return. The act of giving has been seen as one of humankind’s greatest attributes throughout history. It is honored in nearly every culture. To give is a gift to both those who receive and those who give. Giving is usually associated with addressing the material needs of others, but the gift given can take many forms such as wisdom or protection or simply a shoulder to cry on.
As a daily card, Altruism suggests there are those around you in need of things you can give them. It is a time for you to address the needs of another, or others without regard of profit or acknowledgement of your contribution.