Thinking Outside the Classroom: Venus to pass through Pleiades, the Seven Sisters on April 3 |

Thinking Outside the Classroom: Venus to pass through Pleiades, the Seven Sisters on April 3

Mark Laurin
Thinking Outside the Classroom
Every eight years, Venus has a close encounter with the Pleiades star cluster. Often mistaken for the Little Dipper in our winter sky, the Pleiades cluster is also known as the Seven Sisters and Messier 45. The last passage of Venus by the Pleiades happened in spring 2012, as seen in this image. Eight years later, Venus returns to the Pleiades cluster this spring for a beautiful evening spectacle.
Jimmy Westlake / Steamboat Pilot & Today

Mark April 3 on your calendar between sunset and midnight to witness with your naked eye the majesty of Venus as it passes through the open star cluster of Pleiades in our western sky.

For astronomers, 2020 is the year of the planets. And it is an exceptional year for Venus, our second planet from the sun and the second-brightest natural object in the night after the moon. Speaking of moons, Venus doesn’t have one. Venus is currently putting on its best show in eight years by making many superb appearances in the evening and the morning. In fact, it is because the planet’s movements appear to be discontinuous — appearing and then disappearing on one horizon, and then reappeaing on the opposite horizon — that many cultures did not recognize Venus as a single entity. Rather, it was assumed to be two different stars on each horizon. Since Venus lies within Earth’s orbit, as an inner planet, it never appears to venture farther than 47 degrees from the sun. 

Venus, a goddess by any other names

The Egyptians and Greeks believed Venus to be two separate bodies, a morning star and an evening star. The Greeks used the names Phosphoros, meaning “light-bringer,” and Heosphoros, meaning “dawn-bringer.” The Sumerians, the first to understand that the morning star and the evening star were in fact the same object, associated the planet with the goddess, Inanna. In the Old Babylonian period, the planet Venus was known as Ninsi’anna. The name translates to “divine lady, illumination of heaven.” In Chinese, the planet is called Jīn-xīng, and for the Romans, Venus was the goddess of love and beauty. In the Maya culture, Venus was considered the most important celestial body observed naming it Chac ek, “the great star.”

Pleiades, an open cluster

The Pleiades, also known as the Seven Sisters and Messier 45, is an open star cluster located in the constellation of Taurus. Galileo Galilei was the first astronomer to view the Pleiades through a telescope. The Frenchmen, Charles Messier, measured the position of the cluster and identified it as M45 (the “M” is for Messier) in his 1771 catalogue of 100 comet-like objects. An open cluster is a group of up to a few thousand stars that were formed inside the same giant molecular cloud and have roughly the same age. The cluster’s core radius is about eight light-years and contains more than 1,000 confirmed stars. Its light is dominated by young, hot blue stars to middle-aged stars, up to 14 of which can be seen with the naked eye. The seven brightest are known as the Seven Sisters, which is somewhat similar in shape to Ursa Major (Big Dipper) and Ursa Minor (Little Dipper) which is why Pleiades is informally referred as the “Mini Dipper.”   

The Pleiades have been known since antiquity to cultures all around the world from the Celts, Hawaiians, the Persians, the Chinese and Aztec. The Sioux and Cherokee mention the Pleiades, along with the Bible. Have you ever looked close at the logo for the Japanese automobile manufacturer Subaru? In Japan, the open cluster is known as Subaru. It was chosen as the brand name of Subaru automobiles to acknowledge the origins of the firm as the joining of five companies. It is depicted in its six-star logo.

Viewing Venus passing though Pleiades

First, get outside after sunset April 3 and look at the western horizon and then look just shy of halfway up from the horizon to directly overhead. Venus is hard to miss. It’s been riding high in the western evening sky for the past few months, and its brightness can be confused with the landing lights of an approaching airplane! Find Venus first, and the Pleiades will frame the planet within the Seven Sisters. When you observe Venus through binoculars or a telescope, you’ll see a shroud: an opaque layer of highly reflective clouds of sulfuric acid. This shroud prevents its surface from being seen, which is consequently why it is so luminous. Also, when you view it through a telescope or binoculars, look at the brilliant blue color for the Seven Sisters. A star’s color indicates its age; these stars are young, only about 100 million years old. While you have your eye on the eyepiece, try and count the 14 major stars and notice the gray wisps around the blue stars. This is a reflection nebulosity made of interstellar dust thought to be leftover material from the formation of the cluster.   

Mark Laurin is a Keystone Science School volunteer.

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