April 2018

Welcome to SkyEye, your guide to this month's celestial events.

The Calendar

Date Body Event
1 Mercury inferior conjunction
2 Mars, Saturn 1.3° apart
7 Moon, Saturn 1.9° apart
8 Moon apogee
Moon last quarter
10 Moon descending node
12 Moon, Neptune 1.9° apart
13 136199 Eris conjunction
14 Mercury stationary point: retrograde → direct
136108 Haumea opposition
16 Moon new
17 Saturn aphelion
18 Saturn stationary point: direct → retrograde
Uranus conjunction
19 Moon occultation of Aldebaran: visible from northcentral North America, northeastern Europe and northcentral Asia
20 Moon perigee
22 Earth Lyrid meteor shower
Moon first quarter
23 Moon 1.6° south of the open star cluster M44 (known as Praesepe or the Beehive Cluster)
Mercury aphelion
Moon ascending node
24 Earth π Puppid meteor shower
Moon occultation of Regulus: visible from northcentral Asia.
29 Mercury greatest elongation west (27.0°)
30 Moon full

The Solar System

The word planet is derived from the Greek word for 'wanderer'. Unlike the background stars, planets seem to move around the sky, keeping mostly to a narrow track called the ecliptic, the path of the Sun across the stars. Dwarf planets and small solar-system bodies, including comets, are not so constrained, often moving far above or below the ecliptic.

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Sun PiscesAries

Mercury PiscesCetusPisces

Mercury is at inferior conjunction on the first day of the month, passing from the evening to the morning sky. It is best viewed in the southern hemisphere where it rises high in the east before sunrise. Northern observers, however, have a poor view of this elusive planet this month. Mercury reaches a stationary point on 14 April, going from retrograde to direct motion, and attains greatest elongation west on the penultimate day of the month.

Venus AriesTaurus

As seen from the northern hemisphere, the evening star is rising rapidly above the western horizon.

Earth and Moon

The First Quarter Moon will be setting around the time that the radiant of the Lyrid meteor shower rises on 22 April so moonlight should not be a problem in the early morning hours. Theory suggests maximum activity will occur around 18:00 UT. Two days later, the waxing gibbous Moon is more of an issue for the π Puppid meteor shower but the radiant is still aloft after midnight when the skies will be darker. Theoretical maximum is at 00:00 UT.

The path of the Moon across the sky occasionally takes it in front of a first-magnitude star. This month it happens twice. Aldebaran is eclipsed on 19 April. Five days later, another such occultation occurs when the Moon obscures Regulus in the constellation of Leo. This is the last in a series of 19 occultations which began in December 2016. The next Regulus series won't begin until July 2025.

Mars Sagittarius

The red planet meets the ringed planet on the second day of the month when Mars and Saturn come within 1.3° of each other. Both objects lie south of the celestial equator, making this naked-eye spectacle easier to observe from equatorial and southern latitudes.

Jupiter Libra

Like the two other bright superior planets, Jupiter is easier to see the farther south you are on Earth. It rises before midnight but is best observed in the early morning hours.

Saturn Sagittarius

The ringed planet now rises before midnight for all terrestrial observers. It is found near Mars on 2 April and has nearly as close of an encounter with the Moon five days later. A once-in-thirty-years event happens on 17 April, when Saturn reaches aphelion, the point in its orbit when it's farthest from the Sun. The following day, Saturn reverses direction in the sky, going into retrograde.

Uranus PiscesAries

At solar conjunction on the eighteenth day of the month, Uranus is unobservable throughout April.

Neptune Aquarius

A small telescope is necessary to view the most distant planet in the solar system. It may be far enough removed from the solar glare to be visible in the early morning hours so look for it on 12 April when the waning crescent Moon passes close by.

The Celestial Sphere

Constellations are patterns of stars in the sky. The International Astronomical Union recognises 88 different constellations. The brightest stars as seen from the Earth are easy to spot but do you know their proper names? With a set of binoculars you can look for fainter objects such as nebulae and galaxies and star clusters or some of the closest stars to the Sun.

Descriptions of the sky for observers in both the northern and southern hemispheres are available for the following times this month. Subtract one hour from your local time if summer (daylight savings) time is in effect.

Local Time Mid-month Northern Hemisphere Equator Southern Hemisphere
1730 hours (1830 hours summer time) 60° N 50° N 40° N 30° N 20° N 10° N 10° S 20° S 30° S 40° S
1930 hours (2030 hours summer time) 60° N 50° N 40° N 30° N 20° N 10° N 10° S 20° S 30° S 40° S
2130 hours (2230 hours summer time) 60° N 50° N 40° N 30° N 20° N 10° N 10° S 20° S 30° S 40° S
2330 hours (0030 hours summer time) 60° N 50° N 40° N 30° N 20° N 10° N 10° S 20° S 30° S 40° S
0130 hours (0230 hours summer time) 60° N 50° N 40° N 30° N 20° N 10° N 10° S 20° S 30° S 40° S
0330 hours (0430 hours summer time) 60° N 50° N 40° N 30° N 20° N 10° N 10° S 20° S 30° S 40° S
0530 hours (0630 hours summer time) 60° N 50° N 40° N 30° N 20° N 10° N 10° S 20° S 30° S 40° S