April is named for aprilis, which means opening, or aperture. That is what the northern hemisphere is doing in this the first full month of spring. The nights are getting shorter, but warmer. That makes this a great time to get out under the stars.

There are several highlights this month. Mercury will be at its highest and brightest for the year in the evening sky during the first week. Jupiter will reach opposition on April 7; Saturn will begin its westward motion one day before that on the way to its own opposition in June; Mars will pass between the Pleiades and Hyades star clusters in Taurus; and Venus will make a dramatic morning appearance, rapidly climbing higher in the sky. The Lyrid meteor shower peaks on the 22nd. There will be a couple of good comets, one of which may even become visible without binoculars. Another bonus will be two asteroids visible in Leo, but you will need a small telescope to see with these primordial objects orbiting the sun between Mars and Jupiter.

Our first and fastest planet, Mercury, will be at its very best during the first few evenings this month. It will reach its greatest eastern elongation from the sun at 19 degrees, and it will not set until about 9 p.m. Look for it about 15 degrees below and to the right of Mars in the evening sky, in about the same location that Venus was last month.

Mars continues to slowly fade and move eastward, one constellation per month, roughly keeping up with our own progress around the sun. We will not lose Mars completely in our western sky until about one month into summer. Like a cruise ship sailing through the newly opened Northwest Passage, watch closely as Mars cruises between two distinct star clusters in Taurus, the famous Pleaides, or Seven Sisters, and the less famous Hyades. This will start on the April 21 and the red planet will finish its remarkable passage by the end of the month.

In reality Mars is now over 200 million miles away, which is about as far away as it can get from us. That is about 20 minutes at the speed of light. Mars could get as close as 33 million miles at opposition. The next Mars opposition is not until July 2018 and the last one was in May 2016. The red planet will continue to drift farther from us until about the start of summer.

The Hyades star cluster, which marks the face of Taurus, contains about 400 stars and is only 150 light years away, making it the closest star cluster to Earth. The bright orange star near the Hyades, Aldebaran, is not part of the cluster since it is only 65 light years away, along our line of sight to the Hyades. The Pleiades are not related to the Hyades, either. The Seven Sisters are about 400 light years away and contain about 500 stars.

The Hyades star cluster is related to the Beehive cluster in Cancer. These clusters came from a common source in the Milky Way and have been migrating away from that location since. We know that based on the age of their stars, their metallicity and their proper motion around the center of our galaxy.

Since we are always looking back in time as we look into space, we are not seeing the Pleiades as they are now, but rather how they looked about 400 years ago, or the time of Galileo. Knowing the distance to a celestial object when you look at it through a telescope ties you into what was happening on Earth at that time. When you look at the Hyades cluster, be aware that our Civil War was just ending about that time, 150 years ago.

Or you could go deeper into space and look at a galaxy in Leo that is 65 million light years away, remembering that is when the last dinosaur died. A comet or asteroid hit the earth then, and its 150-mile-wide crater is visible under the Gulf of Mexico just off the Yucatan. That crater was found less than 30 years ago since it is underwater.

If there is a highly intelligent civilization in a galaxy that distance from us that can see the surface of Earth through some kind telescope or other instrument, they could see, right now, this very second, exactly what happened to create that mass extinction.

Jupiter will reach its opposition on April 7. That means that it will rise exactly at sunset, reach its highest point in our sky at midnight, and not set until sunrise. That is similar to a full moon, which reaches opposition every month while Jupiter and Saturn only reach it once every 13 months or so. That is the best time to view a planet since it will be at its closest and largest and brightest for the year at that time.

Saturn now rises about 1 a.m. and will end its normal, eastward motion a day before Jupiter reaches opposition. Saturn reaches opposition on June 15.

APRIL HIGHLIGHTS

April 1: Mercury is near Mars in the evening sky.

April 3: First quarter moon is at 2:39 p.m.

April 6: Saturn is stationary in the sky before starting its retrograde motion the next day.

April 7: The moon passes very close to Regulus this morning. Jupiter is at opposition. The Compton Gamma Ray Observatory was deployed in 1991.

April 10: The moon passes near Jupiter this evening.

April 11: Full moon is at 2:08 a.m. This is also called the Grass, Egg or Pink Moon. Halley’s Comet was closest to Earth in 1986.

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

April 16: Wilbur Wright was born in 1867.

April 19: Last quarter moon is at 5:57 a.m.

April 22: The Lyrid meteor shower peaks this morning after midnight. You could see up to 15 meteors per hour, all emanating from the constellation Lyra. These meteors are caused by the earth’s passing through the debris trail of Comet Thatcher. This is also Earth Day. The first one was in 1970, just after we saw pictures of the Earth from space from our first moon trip in 1969.

April 23: The moon passes near Venus this morning.

April 25: The Hubble Space Telescope was deployed in 1990. It has taken over a million images and transformed our view of the universe. It was a bigger leap in knowledge than when Galileo made his discoveries.

April 28: The moon passes near Mars this evening. Jan Oort was born in 1900. The Oort cloud, the source of our comets, was named after him.

April 29: Venus reaches its greatest brightness in the morning sky at minus 4.7 magnitude.

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