Australian Sky & Telescope - April 2018

46 AUSTRALIAN SKY & TELESCOPE April 2018

SUN, MOON & PLANETS by Jonathan Nally

Mercury masters the morning

This is a good time to spot the innermost planet.

A

pril will see four of the bright

naked-eye planets visible together

in the early morning hours, with

Jupiter, Saturn and Mars all rising in the

late evening, and Mercury joining them

in the pre-dawn sky. Venus is an evening

planet; by the end of April, it and Jupiter

will be seen above opposite horizons

(west and east, respectively) at dusk.

Mercury (mag. 1.7, diameter 10.5 ̋

on April 15; mag. 0.3 and 8.0 ̋ by

month’s end) will be at its best in the

morning from early April through to

mid-May, visible in the eastern sky

before sunrise. The innermost planet

will have reached inferior conjunction

(ie. between the Earth and the Sun)

on April 2, and will then begin to rise

higher above the eastern horizon with

each passing day, reaching a maximum

angle(orelongation)fromtheSunof27

degreesonApril30.Thiswillbethebest

morningapparitionofMercuryfor2018,

somakesureyougrabthisopportunity

togetyourtelescopeoutandtakealook

at this mysterious world.

Venus(–3.9, 11.0 ̋) is t he e ve n i ng

‘star’ during April, and will remain so

right through until mid-October. The

bright planet will be in the constellation

Taurus,andwillappearclosetothe

Pleiades (Messier 45) from April 23 to

26.ThethincrescentMoonwillgetin

on the act too, coming fairly close on

April 18.

Mars(0.0,9.5 ̋)isalateriserin

April, coming up over the horizon at

about11:00pmatthebeginningof

themonth,andjustafter10:00pm

bymonth’send.Tobefoundin

Sagittarius, the Red Planet will make

a few interesting pairings this month,

including coming close to the third-

brightestglobularstarcluster,Messier

22, in the first week of April. The

ringedplanet,Saturn,willbecloseat

the beginning of the month, too (see

STwo planets, the Moon and a globular star

cluster will form a nice grouping.

STheMoonwillvisitAldebaranandthe

Hyades in Taurus, with Venus below.

diagram below), with the two worlds

coming within 1.2 degrees of each

other. Take a look through binoculars

— it’ll be a great sight. The waxing

Moon will appear close to Mars, too,

coming within 4 degrees on April 7,

with Saturn above them to form a nice

triangle. Mars is heading for opposition

in July — opposition is when a planet

and the Sun are on opposite sides of the

Earth, the practical upshot of which is

the planet rises in the east as the Sun

sets in the west, and therefore you have

all night long in which to make your

observations. This’ll be the best Mars

opposition since 2003, with the planet

to reach a brightness of magnitude –2.8

and an apparent diameter of just over

24 arcseconds.

Jupiter(–2 .4, 4 4 ̋) is c u r r e nt ly

undergoing retrograde motion as our

planet laps it on our interior orbit. The

KingofthePlanetsrisesataround

8:00pm at the beginning of April, and by

around 6:00pm at month’s end. Heading

for opposition in May, the giant world

will make a great sight through even a

small telescope; make sure you follow

the movements of its four Galilean

satellites as they change position from

night to night. Also keep an eye out for

two pairings between the planet and our

Moon, on the 3rd and 30th.

Saturn (0.4, 17 ̋) is another late

riser, coming up over the horizon at

roughly the same time as Mars at

month’s beginning, and by just after

9:00pm at month’s end. And like Mars,

the planet is in Sagittarius and will

appear close to Messier 22 at the start

of the month. Watch for the Moon

nearby on the 7th. Saturn will reach the

stationarypointinitsorbitonApril18,

andwillthenbeginalmostfivemonths

ofretrogrademotion(again,asthe

Earth overtakes it on the inside track).