This Month’s Sky – April 2016

What’s Up in the Sky
AAA Observers’ April Guide
By Tony Faddoul



April’s Evening Planets:
Jupiter will be in Leo the Lion all night this month. Mercury is between Pisces the Fish and Aries the Ram for an hour after sunset in the middle of April. Mars will be in Scorpio the Scorpion. Saturn will be between Scorpio and Ophiuchus the Serpent Bearer as of midnight and rising earlier every night until 10 PM by the end of the month.

April’s Evening Stars:
The Winter Triangle will be up in April until around 10 PM: Sirius, the brightest star viewed from Earth is in Canis Major the Great Dog, Betelgeuse is in Orion the Hunter, and Procyon is in Canis Minor the Small Dog. Spot Capella in Auriga the Charioteer, Aldeberan in Taurus the Bull, and bright Castor and Pollux in Gemini the Twins. Also find the stars of constellations Cassiopeia, Hercules, Perseus, Draco, Virgo, Leo, Libra, and Ursa Major and Ursa Minor (the Big and Little Dippers).

April’s Morning Planets:
Venus will be in Pisces for an hour before sunrise. Mars will be in Scorpio, and Saturn will be between Scorpio and Ophiuchus until sunrise. Jupiter can be seen in Leo until sunrise, setting earlier every night until 4 AM by the end of April. Neptune is in Aquarius the Water Bearer for about 2 hours before sunrise. Dwarf Pluto is in Sagittarius the Archer from 3 AM until sunrise.

April’s Morning Stars:
Spot the Summer Triangle of Vega in Lyra the Harp, Deneb in Cygnus the Swan, and Altair in Aquila the Eagle as of 2 AM and earlier every night. Look for reddish Antares in Scorpius, Arcturus in Boötes the Herdsman, and Spica in Virgo the Virgin, along with the stars of constellations Leo, Hercules, Libra, Sagittarius, Cassiopeia, Draco, Ursa Major, and Ursa Minor.

April “Skylights”

Apr 6 Venus is 0.6° south of Moon dawn
Apr 7 New Moon at 7:25 AM
Moon at perigee (221,900 miles away)
Apr 13 First Quarter Moon at 11:59 PM
Apr 16 Mars stationary
Apr 18 Jupiter 2° north of Moon at midnight
Apr 22 Full Moon at 1:25 AM
Moon at apogee (252,500 miles away)
Apr 23 Lyrid meteor shower peaks dawn
Apr 24 Mars 5° south of Moon at midnight
Apr 28 Mercury stationary at midnight
Apr 29 Last Quarter Moon at 11:30 PM
Times given in EDT.

Occultation of Aldebaran
This month, one of the brightest stars in the sky will dis-appear from view, blotted out by the Moon. The lunar occultation of Aldebaran has been observed for over 1,500 years, and its regularity can be predicted. The Apr 10 lunar occultation of the bright, orange star is one of a current series of 49 events that began in Jan 2015 and will continue until Sep 2018. Occurring roughly every 18 years, the next series won’t begin until 2033.

What is occultation?
Occultation occurs when one celestial object passes in front of another and ob-scures it from view. It happens more often with faint stars, but the bright first-magnitude Aldebaran will disappear behind a crescent Moon in the late afternoon of Apr 10, winking out of sight, and reappearing at nightfall as the Moon passes.

What is the history behind Aldebaran?
The regular lunar occultation of Aldebaran led to the discovery of the proper motion of stars. By observing the occultation, Edmund Halley calculated in the 1700s that Aldebaran must have changed its position in the sky over time. About 450,000 years ago, Aldebaran was actually the North Star. In fact, it shared that honor with Capella, as those two stars were very close together in the sky at the time. Despite our perception that stars are fixed, they are moving through space in orbit around the galactic center, just as the Solar System is also in motion. Meanwhile, Earth’s pole star changes during the 26,000-year precession of the planet’s rotation axis, so positions are always changing over the long-term.

Where can I see the occultation?
The occultation of Aldebaran is only visible in the Northern hemisphere. It can be seen in the New York area and along the Atlantic coast, and you can view the phenomenon with the naked-eye under clear skies by looking west to the cres-cent Moon. Then, look for the Pleiades and Aldebaran, the “eye” in the constellation Taurus the Bull. The star will hide behind the dark side of the Moon and reappear on the lit side.

What is the Ancient Greek myth behind Taurus?
Europa was the beautiful daughter of the Phoenician king of Tyre. Overwhelmed by love, the god Zeus transformed him-self into a magnificent white bull and seduced her. With Europa on his back, he swam to the island of Crete, where she became a queen. The continent Europe is named for her. Zeus recreated the bull’s shape in the stars of the constellation Taurus.