WHAT'S UP THIS MONTH - APRIL 2021

(Link to What's Up March 2021)

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THESE PAGES ARE INTENDED TO HELP YOU FIND YOUR WAY AROUND THE SKY

The chart above shows the whole night sky as it appears on 15th April at 22:00 (10 o'clock) British Summer Time (BST). As the Earth orbits the Sun and we look out into space each night the stars will appear to have moved across the sky by a small amount. Every month Earth moves one twelfth of its circuit around the Sun, this amounts to 30 degrees each month. There are about 30 days in each month so each night the stars appear to move about 1 degree. The sky will therefore appear the same as shown on the chart above at 9 o'clock BST at the beginning of the month and at 11 o'clock BST at the end of the month. The stars also appear to move 15º (360º divided by 24) each hour from east to west, due to the Earth rotating once every 24 hours.

The centre of the chart will be the position in the sky directly overhead, called the Zenith. First we need to find some familiar objects so we can get our bearings. The Pole Star Polaris can be easily found by first finding the familiar shape of the Great Bear ‘Ursa Major' that is also sometimes called the Plough or even the Big Dipper by the Americans. Ursa Major is visible throughout the year from Britain and is always quite easy to find. This month it is directly over head. Look for the distinctive saucepan shape, four stars forming the bowl and three stars forming the handle. Follow an imaginary line, up from the two stars in the bowl furthest from the handle. These will point the way to Polaris which will be to the north of overhead at about 50º above the northern horizon. Polaris is the only moderately bright star in a fairly empty patch of sky. When you have found Polaris turn completely around and you will be facing south. To use this chart, position yourself looking south and hold the chart above your eyes.

Planets observable in the evening sky: Mars.

 

EXPLORING THE NIGHT SKY THIS MONTH

The night sky looking south at about 22:00 BST on 15th April

The chart above shows the night sky looking south at about 22:00 BST on 15th April. West is to the right and east to the left. The point in the sky directly overhead is known as the Zenith and is shown (in red) at the upper centre of the chart. The curved brown line across the sky at the bottom is the Ecliptic or Zodiac. This is the imaginary line along which the Sun, Moon and planets appear to move across the sky. The brightest stars often appear to form a group or recognisable pattern; we call these ‘Constellations'.

Constellations through which the ecliptic passes this month are Aries (the Ram), Taurus (the Bull), Gemini (the Twins), Cancer (the Crab), Leo (the Lion), Virgo (the Virgin) and Libra (the Scales).

Moving towards the south western horizon is the constellation of Taurus (the Bull). The most obvious star in Taurus is the lovely Red Giant Star called Aldebaran. It appears slightly orange to the ‘naked eye' but it is very obviously orange when seen using binoculars or a telescope. Aldebaran is located at the centre of the ‘flattened' X shape formed by the brightest stars in Taurus. Aldebaran appears to be in a cluster of stars known as the Hyades but it is not a true member and is much closer to us than the other stars. The bright orange planet Mars is in Taurus so we must make sure we do not confuse Mars with Aldebaran.

At the end of the top right (upper west) arm of the ‘X' of Taurus is the beautiful ‘naked eye' Open Star Cluster Messier 45 (M45) known as the Pleiades (or the Seven Sisters). It really does look magnificent using binoculars. Just above the star at the end of the lower left arm of the ‘X' is the faint Supernova Remnant Messier 1 (M1) the Crab Nebula. This exploding star was seen as a bright new star in 1054 and can still be seen as a faint patch of light using a medium telescope but a really dark and clear sky is required.

Following Taurus is the constellation of Gemini (the Twins). The two brightest stars in Gemini are Castor and Pollux that are named after mythological twins. To the north of Taurus is the odd pentagon shape of Auriga (the Charioteer). Dominating Auriga is the brilliant white star Capella which is almost overhead in the early evening. For those with a telescope there is a line of lovely open clusters to search out in Taurus and Auriga. These are M35 in Taurus and M36, M37 and M38 in Auriga.

To the east (left) of Gemini is the rather indistinct constellation of Cancer (the Crab). The stars of Cancer are quite faint and can be difficult to discern especially in a light polluted sky. It is worth searching out Cancer using binoculars or a telescope to see the Open Cluster M44 Praesepe (the Beehive Cluster). M44 is older and further away than M45 (the Seven Sisters) so is fainter but still looks lovely. It has a group of stars that resemble an old straw Beehive with bees around it.

To the south of Taurus and Gemini is the spectacular constellation of Orion (the Hunter). Orion is one of the best known constellations and hosts some of the most interesting objects for us amateur astronomers to seek out. Orion was the February constellation of the month.

The constellation of Leo (the Lion) follows Cancer along the Ecliptic and will be the constellation of the month next month. It does actually look a little like a lion or the Sphinx in Egypt. Around and between Leo and the neighboring constellation of Virgo is a cluster of galaxies. Our Milky Way galaxy and our local group of galaxies are members of this larger group of galaxies called the Virgo Cluster. A medium sized telescope (150mm to 200mm) and a dark sky is required to see these faint objects.

 

GUIDE TO THE CONSTELLATIONS THIS YEAR

The constellations in January

The chart above shows the positions of the constellations as they appeared in the beginning of this year, in the middle of January (15th ). In this chart the whole sky is displayed from the southern horizon to the northern horizon and from the eastern horizon to the western horizon. At the centre of the chart the point directly overhead is marked in red as the ‘ZENITH'. The point on the ground below our Zenith is the town of Newbury (our observing location).

The night sky is divided into 88 areas that we call the ‘CONSTELLATIONS'. These areas are based around noticeable groups of the brightest stars that are shown on the chart as joined up as dot to dot ‘stick figures'. The constellations are named after characters from mythology and in many cases are very old.

Across the centre of the chart is a curved brown line this is called the Ecliptic (or the Zodiac). This is the imaginary line along which the Sun, Moon and planets appear to move across the sky as Earth rotates once a day (24 hours). It is also the position of the plane of the equator of the Sun and Solar System. The ecliptic appears to move up and down and around the sky due to the axis of Earth being tilted at an angle of 23.4º to the plane of the Solar System. This is noticeable on the following monthly charts as it is related to the annual seasons on Earth.

 

TABLE OF ALL 88 CONSTELLATIONS

Some stars appear to be in groups so these groups can also be used to find our way around the sky and we call these groups ‘Constellations'. There are 88 internationally recognised constellations that are shown: Zodiacal ( bold red ), Northern (normal) and Southern ( gray ).

So what are constellations? Some bright stars appear to form patterns in the sky and are called constellations. The brightest stars are joined by lines to denote the grouping for each constellation. Many of the constellations in the northern hemisphere are named after characters from Greek mythology and mostly originate from ancient times. Here is a table listing all 88 constellations and the following charts show the view of constellations each month.

NAME

DESCRIPTION

 

NAME

DESCRIPTION

Andromeda

Daughter of Cassiopeia

 

Lacerta

Lizard

Antlia

Air Pump

 

Leo

Lion

Apus

Bird of Paradise

 

Leo Minor

Little Lion

Aquarius

Water-Bearer

 

Lepus

Hare

Aquila

Eagle

 

Libra

Balance

Ara

Altar

 

Lupus

Wolf

Aries

Ram

 

Lynx

Lynx

Auriga

Charioteer

 

Lyra

Lyre

Boötes

Herdsman

 

Mensa

Table

Caelum

Chisel

 

Microscopium

Microscope

Camelopardalis

Giraffe

 

Monoceros

Unicorn

Cancer

Crab

 

Musca

Fly

Canes Venatici

Hunting Dogs

 

Norma

Square

Canis Major

Big Dog

 

Octans

Octant

Canis Minor

Little Dog

 

Ophiuchus

Serpent-Bearer

Capricornus

Goat

 

Orion

Hunter

Carina

Keel (of Argo)

 

Pavo

Peacock

Cassiopeia

Queen

 

Pegasus

Winged Horse

Centaurus

Centaur

 

Perseus

Rescuer of Andromeda

Cepheus

King

 

Phoenix

Phoenix

Cetus

Whale

 

Pictor

Painter

Chamaeleon

Chameleon

 

Pisces

Fishes

Circinus

Compasses

 

Piscis Austrinus

Southern Fish

Columba

Dove

 

Puppis

Stern (of Argo)

Coma Berenices

Berenice's Hair

 

Pyxis

Compass

Corona Australis

Southern Crown

 

Reticulum

Reticle

Corona Borealis

Northern Crown

 

Sagitta

Arrow

Corvus

Crow

 

Sagittarius

Archer

Crater

Cup

 

Scorpius

Scorpion

Crux

Cross

 

Sculptor

Sculptor

Cygnus

Swan

 

Scutum

Shield

Delphinus

Dolphin

 

Serpens

Serpent

Dorado

Swordfish

 

Sextans

Sextant

Draco

Dragon

 

Taurus

Bull

Equuleus

Little Horse

 

Telescopium

Telescope

Eridanus

River

 

Triangulum

Triangle

Fornax

Furnace

 

Triangulum Australe

Southern Triangle

Gemini

Twins

 

Tucana

Toucan

Grus

Crane (bird)

 

Ursa Major

Great Bear

Hercules

Son of Zeus

 

Ursa Minor

Little Bear

Horologium

Clock

 

Vela

Sails (of Argo)

Hydra

Water Snake (female)

 

Virgo

Maiden

Hydrus

Water Snake (male)

 

Volans

Flying Fish

Indus

Indian (American)

 

Vulpecula

Fox

 

THE OBSERVABLE SKY

A chart showing the Celestial view of our night sky April 2021

Our planet is tilted over at 23.4º to the plane of the Solar System so the northern axis of rotation of Earth is aligned on a point in the sky near to the star Polaris. Over the course of our 24 hour day the whole sky appears to rotate around Polaris. This makes Polaris the only star that does not move as the sky appears to rotate. As it is always in the same place and to the north of the Zenith (the point directly overhead) we also call Polaris the ‘North Star' or the ‘Pole Star'.

The red grid marked on the chart above is called the Celestial Grid so the vertical lines are drawn from the North Celestial Pole Axis Point to the South Celestial Pole Axis Point. The horizontal lines are 20º divisions from the North Pole. We measure the angular distance from the North ‘Celestial' Pole to the Celestial Equator as 90º to 0º and 0º to -90º from the Celestial Equator to the South Celestial Pole.

It can be seen from the chart above that area of sky that rotates past the South point on the Southern Horizon and up to the North Axis of Rotation (Polaris) is larger than from North point on the Northern Horizon to Polaris. The actual difference is; Northern Horizon to Polaris 51.4º and from Polaris to the Southern Horizon 128.6º. So there is 38.6º from Polaris to the Zenith (the point directly overhead from Newbury).

For the reasons above we normally set up our telescopes to look south (because there is more sky moving through our view as Earth rotates). There is another major reason to look towards the south; this is because it is the direction that we see the Planets, the Moon and the Sun pass through our view. The Planets, the Moon and the Sun appear to move along the imaginary line across the sky that we call the Ecliptic which is the equator of the Solar System. The Ecliptic is marked on the following charts that show the monthly view of the sky to the South. As Earth moves around the Sun we see different constellations passing by throughout the year.

The following charts show how our view of the night sky changes through the year due to Earth moving around the Sun on its orbit. As we look out into space at the night sky we see the stars move from east to west 360º divided by 365 = 1º each night (approximately). So every month the night sky will appear to have moved 360º divided by 12 = 30º from east to west. This means 30º of sky has moved into view over the eastern horizon and 30º of the sky will have disappeared over the western horizon.

THE NIGHT SKY IN JANUARY

The constellations through which the ecliptic passes during January are Aquarius (the Water Carrier), Pisces (the Fishes), Aries (the Ram), Taurus (the Bull), Gemini (the Twins), Cancer (the Crab) and Leo (the Lion). Orion is dominating the southern sky at this time of the year.

THE NIGHT SKY IN FEBRUARY

The constellations through which the ecliptic passes during February are Aquarius (the Water Carrier), Pisces (the Fishes), Aries (the Ram), Taurus (the Bull), Gemini (the Twins), Cancer (the Crab), Leo (the Lion) and Virgo (the Virgin). Orion is still well placed.

THE NIGHT SKY IN MARCH

The constellations through which the ecliptic passes during March are Aquarius (the Water Carrier), Pisces (the Fishes), Aries (the Ram), Taurus (the Bull), Gemini (the Twins), Cancer (the Crab), Leo (the Lion) and Virgo (the Virgin). Orion is moving towards the western horizon.

THE NIGHT SKY IN APRIL

The constellations through which the ecliptic passes during April are Aries (the Ram), Taurus (the Bull), Gemini (the Twins), Cancer (the Crab), Leo (the Lion), Virgo (the Virgin) and Libra (the Scales). Orion has now moved over the western horizon.

THE NIGHT SKY IN MAY

The constellations through which the ecliptic passes during May are Gemini (the Twins), Cancer (the Crab), Leo (the Lion), Virgo (the Virgin) and Libra (the Scales) rising over the eastern horizon. The constellation of Sagittarius will rise in the east later in the evening.

THE NIGHT SKY IN JUNE

The constellations through which the ecliptic passes during are: Gemini (the Twins), Cancer (the Crab), Leo (the Lion), Virgo (the Virgin), Libra (the Scales) and Sagittarius (the Goat) rising over the South Eastern horizon. The Summer Triangle is now making an appearance in the east and Ecliptic appears very low in the midsummer night sky on 21st June (the Summer Solstice).

THE NIGHT SKY IN JULY

The constellations through which the ecliptic passes during July are Leo (the Lion), Virgo (the Virgin), Libra (the Scales), Sagittarius (the Goat) and Aquarius (the Water Carrier). The Summer Triangle is now prominent in the southern sky.

THE NIGHT SKY IN AUGUST

The constellations through which the ecliptic passes during August are Libra (the Scales), Sagittarius (the Goat), Aquarius (the Water Carrier), Pisces (the Fishes) and Aries (the Ram). The Summer Triangle is now prominent in the southern sky.

THE NIGHT SKY IN SEPTEMBER

The constellations through which the ecliptic passes during September are Libra (the Scales), Sagittarius (the Goat), Aquarius (the Water Carrier), Pisces (the Fishes), Aries (the Ram) and Taurus (the Bull). The Summer Triangle is now moving towards the western horizon.

THE NIGHT SKY IN OCTOBER

The constellations through which the ecliptic passes during October are Libra (the Scales), Sagittarius (the Goat), Capricornus (the Goat), Aquarius (the Water Carrier), Pisces (the Fishes), Aries (the Ram), Taurus (the Bull) and Gemini (the Twins).

THE NIGHT SKY IN NOVEMBER

The constellations through which the ecliptic passes during November are Capricornus (the Goat), Aquarius (the Water Carrier), Pisces (the Fishes), Aries (the Ram), Taurus (the Bull), Gemini (the Twins) and Cancer (the Crab). Orion is now moving in from the East.

THE NIGHT SKY IN DECEMBER

The constellations through which the ecliptic passes during December are Aquarius (the Water Carrier), Pisces (the Fishes), Aries (the Ram), Taurus (the Bull), Gemini (the Twins), Cancer (the Crab) and Leo (the Lion). Orion is now dominating the southern sky and the Ecliptic will be at its highest in the midwinter night sky on 21st December (the Winter Solstice).

 

CONSTELLATION OF THE MONTH - CANCER (THE CRAB)

 

The constellation of Cancer (the Crab)

Between the two prominent constellations of Gemini and Leo is the rather indistinct constellation of Cancer (the Crab). The stars of Cancer are quite faint and so the recognisable shape of the constellation can be difficult to identify especially in a light polluted sky. The recognised ‘stick figure' shape of Cancer is an upside down ‘Y' ( ? ).

However it is well worth searching out Cancer using binoculars or a small telescope to see the Open Cluster Messier 44 (M44) known as Praesepe (or the Beehive Cluster). M44 is older and further away than M45 (the Seven Sisters) so is fainter than M45 but still looks lovely. It has a group of stars that resemble an old straw Beehive with bees around it.

Messier 44 (M44) Praesepe the Beehive cluster

M44 is one of the few deep sky objects that look best using binoculars or a small telescope at low power. The image below has been marked to show the old style pyramid shaped straw Beehive with bees around it old straw Beehive with bees around it.

The shape of the old style beehive

The Open Cluster Messier 67 ( M67 also called NGC 2682 ) in Cancer

Messier 67 ( M67 also called NGC 2682 ) is an open cluster in the southern half of Cancer. It is thought to be one of the oldest Open Clusters in our galaxy with estimates of its age ranging between 3.2 and 5 billion years. Distance estimates are also varied and typically are 2,600 – 2,900 light years away.

 

THE SOLAR SYSTEM - APRIL 2021

The planets at 11:00 on 15th April

All the planets except Mars will be difficult to see this month as they are close to the Sun or in daylight.

MERCURY will be rising just before the Sun low in the east this month and will not be visible. The smallest planet will be close to Jupiter and Saturn as they rise in the bright dawn sky later in the month.

VENUS is now too close to the Sun and will not be visible. It was in Superior Conjunction (behind the Sun) on 25th March 2021. It will emerge into the early evening sky in the west over the next few months.

MARS is still well positioned in the evening sky moving through Taurus and will be in the south as the sky darkens. It is getting smaller at about 5.0 arc-seconds as Earth pulls further away. Mars will be around until May but will be moving closer to the south western horizon and appearing smaller. After it has moved over the horizon we will not see it again for two years.

JUPITER will be rising in the South East from about 04:30 and will be visible in the west just before sunrise. Jupiter and Saturn will move further away from the Sun during the year and will be at their best for observing in August. Jupiter will be at opposition on 20th August.

SATURN will be even more difficult to see than Jupiter in the bright early morning sky. The ringed planet rises just before Jupiter in the South West at about 04:00. Saturn will be at its best this year on 2nd August when it will be at opposition and will be due south at midnight.

URANUS will be more difficult to find and will need a telescope. This month it will be in the south west and sets at about 21:00.

NEPTUNE will not be visible this month as it was in conjunction with the Sun on 11th March. It will reappear in the east in the morning sky later in the year.

 

THE SUN

The Sun rises at about 06:25 at the beginning of the month and 05:40 at the end. It sets at 19:40 at the beginning of the month and 18:15 at the end. The Sun has started its phase of increased activity in its eleven years cycle. This cycle is called Cycle 25 at will reach its maximum in about four years time. There have been very few Sunspots recently.

 

THE MOON PHASES DURING APRIL

Last Quarter will be on 4th April

New Moon will be on 12th April

First Quarter will be on 20th April

Full Moon will be on 27th April

 

There will be what we have got used to referring to as a ‘Super Moon' this month. This occurs when the Moon's closest approach to Earth (on its orbit) coincides with Full Moon. The Moon will appear larger because it is closer to us. This full Moon will occur on 27th April.

How the Super Moon will appear in the east

The orbit of the Moon around Earth is not circular it is elliptical therefore it will move closer and further away from Earth on each orbit. When the Moon is at its closest to Earth we call this 'Perigee' and it can be as close as 356,500 kilometres. At its furthest from Earth it can be as far as 406,700 kilometres from Earth and we call this position 'Apogee'. See the diagram below.

When the Moon is at its closest it appears larger and can be up to 14% larger in diameter and 30% larger in area (and brightness) than it appears at its most distant from Earth. The diagram below shows the comparson of how large the Moon can appear at its closest Perigee and smallest at Apogee.

 

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