The month of April is named for aprilis, which means opening. That is what part of the northern hemisphere of the earth is starting to do this month as the days continue to get longer.

There are many interesting highlights to enjoy this month as our long winter finally begins to soften its grip. There will be nice conjunctions of the moon with Venus and then Jupiter, a Mercury and Mars conjunction, Venus giving us a grand tour of the constellation of Taurus, the Lyrid meteor shower, and a total lunar eclipse.

This chart represents the sky as it appears over Maine in April. The stars are shown as they appear at 10:30 p.m. early in the month, at 9:30 p.m. at midmonth and at 8:30 p.m. at month’s end. Jupiter and Venus are shown in their midmonth positions. To use the map, hold it vertically and turn it so that the direction you are facing is at the bottom. Sky chart prepared by George Ayers.

That’s quite a full month of exciting highlights.

Venus continues to brighten in our sky as it catches up with Earth in its faster orbit. It will start this month 78 percent illuminated by the sun but will be only 68 percent illuminated by the end of April. As it travels through Taurus this month, climbing a little higher each night, it will draw attention to interesting features and lead you on an educational tour.

It will start with the Pleiades, also known as the seven sisters, an open cluster of about 500 stars located about 400 light years away and about 100 million years old, then the Hyades, and open cluster of about 200 hundred stars about 130 lights years away and about 600 million years old, or eight times younger than our sun, and then the orange giant star called Aldebaran, which marks the fiery eye of Taurus the Bull.

This orange, spectral type K5 star is about 65 light years away, twice as close as the Hyades that it seems to belong to, and 40 times the diameter of our sun. If you could place Aldebaran in our own sky, it would cover 20 degrees, or two fists at arm’s length, and it would almost include Mercury’s orbit.

Aldebaran means follower in Arabic, since it seems to be following the Pleiades, and it is one of the four royal stars of ancient Persia. The others are Regulus, Antares, and Fomalhaut. They are equally impressive and entirely unique.

The Hyades star cluster is actually related to the Beehive cluster in Cancer, also known as M44. The motions of the stars in these two clusters can be traced back to a common origin in the sky, almost like tracing individual meteors back to one point during a shower, called the radiant. They have other factors in common, like age, metallicity (heavier elements present) and proper motion through our galaxy. The Hyades form a giant oblate spheroid, similar to the shape of the earth, most of which fits into a diameter of about 20 light years across.

As a nice bonus, the slender waxing crescent moon will also travel through Taurus, albeit at a much quicker pace, from the 19th through the 22nd, which is also Earth Day. Notice that Mars and Mercury will form a close conjunction very low in the western sky during that time, 45 minutes after sunset.

Jupiter will end its retrograde motion toward the Beehive on April 8, stopping five degrees short of this relative of the Hyades cluster. Then, the king of the planets will resume its normal eastward or prograde motion in relation to the fixed background of stars for the next eight months, heading back into Leo. Be aware that Jupiter is heading for a great conjunction with Venus on July 1.

Saturn continues to rise a little earlier each night and will be rising by 9:30 p.m. by the end of April. It will reach opposition on May 22 when it will rise exactly at sunset. Notice that the ringed planet is already in retrograde motion, having ended its direct motion on March 14, which was also the once-in-a-century Pi day, when the date and time reflects the first 10 digits of this irrational number, and Albert Einstein’s birthday.

The Lyrid meteor shower peaks on the morning of Wednesday the 22nd. Caused by Comet Thatcher, which only orbits the sun once every 415 years, this shower is not usually too spectacular, only producing about 20 meteors per hour under good conditions. But there are always exceptions, and any reason is a good one for getting out under the stars to enjoy, and to try to understand their vast beauty and power.

The third total lunar eclipse of this very rare tetrad of four total lunar eclipses that also fall on important Jewish holidays will happen on Saturday morning, April 4. This is only the eighth such tetrad in the past 2,000 years. We are not well-placed here on the East coast to see much of this rare event, but we can catch a little of it just before the moon sets in the morning as the sun rises. It will only have entered the penumbral shadow at that point, so you will need binoculars to discern any change at all on the face of the moon. We also missed the total solar eclipse that happened just a few hours before spring started. It occurred at a super moon and was very spectacular over the Faroe Islands, located between Iceland and Norway, and the Svalbard Islands, halfway between Norway and the North Pole.

APRIL HIGHLIGHTS

April 4: Full moon is at 8:05 a.m. This is also called the Grass, Egg, Pink or Fish Moon. The total lunar eclipse will happen today just before sunrise.

April 8: Saturn will be close to the waning gibbous moon this morning.

April 10-12: Venus will be close to the Pleiades in Taurus.

April 11: Halley’s Comet was closest to Earth on this day in 1986. The last-quarter moon is at 11:44 p.m.

April 12: Yuri Gagarin became the first human in space on this day in 1961.

April 16: Wilbur Wright was born in 1867. It was only 66 years after the Wright Brothers made their first very tentative powered flight in 1903 that we traveled to the moon.

April 18: New moon is at 2:57 p.m.

April 19: Mercury and Mars are visible close together low on the western evening horizon. You may need binoculars to see them.

April 20: The slender waxing crescent moon joins Venus by the Pleiades this evening.

April 22: The Lyrid meteor shower peaks tonight.

April 23: Max Planck was born in 1858. He was one of the founders of quantum mechanics that completely redefines what really happens at the very small scale of the universe. The shortest distance in the known universe is called the Planck length, which is 10 to the minus-35 meters. The shortest amount of time, 10 to the minus 43rd second, is called the Planck time. That is the time it takes light to travel the width of a proton. That is also as far back as any humans can possibly see after the instant on the Big Bang.

April 24: In 1970, China became the fifth nation to launch a satellite.

April 25: The Hubble Space Telescope was deployed in 1990. The first-quarter moon is at 7:55 p.m.

April 30: Mercury makes its best evening apparition of the year this week and next.

Bernie Reim of Wells is co-director of the Astronomical Society of Northern New England.

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