WHAT'S UP THIS MONTH - JUNE 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 June 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 almost 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: Venus and Mars.

The Summer Solstice (Midsummer Day) will be on 21st June – The Sun at its highest point at midday 13:00 BST.

EXPLORING THE NIGHT SKY THIS MONTH

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

The chart above shows the night sky looking south at about 22:00 BST on 15th June. 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 Gemini (the Twins), Cancer (the Crab), Leo (the Lion), Virgo (the Virgin), Libra (the Scales), Scorpio (the Scorpion) and Sagittarius (the Archer) just coming into view in the east.

The constellation of Gemini (the Twins) is moving over the western horizon. The two brightest stars in Gemini are Castor and Pollux that are named after mythological twins. Auriga (the Charioteer) is also moving west. The brightest star in Auriga is the brilliant white star Capella which is still visible in the west in the early evening.

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 small 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.

The constellation of Leo (the Lion) follows Cancer along the Ecliptic and is a very interesting constellation. 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.

Following Leo is the less obvious constellation of Virgo but it does have one fairly bright star called Spica. Virgo gives its name to a large cluster of Galaxies that is also spread over into the neighbouring constellations of Coma Berenices (Berenices' Hair) and into Leo.

To the north of Virgo is the bright orange coloured star called Arcturus in the constellation of Boötes. Arctaurus is a Red Giant star that is nearing the end of its ‘life' as a normal star. It has used almost all of its Hydrogen fuel and has expanded to become a Red Giant, 25 times the diameter of our Sun. At the moment it shines 115 times brighter than our Sun but it is destined to collapse and become a White Dwarf.

Higher in the south east is the constellation of Hercules (the Strong Man). Hercules has a rather distinctive distorted square shape, at its centre, called the ‘Keystone'. This is due to its resemblance to the centre stone of an arch or bridge. The jewel of Hercules is without doubt is the Great Globular Cluster, Messier 13 (M13). M13 can be found in the western (right) vertical imaginary line of the ‘Keystone'. It is just visible using a good pair of 9 x 50 binoculars. The spherical cluster, of about a million stars that can be seen using a 90mm f 10 telescope but will look even more impressive when using a larger telescope.

Just moving into the eastern sky is the Summer Triangle that will begin to dominate the Summer Sky.

OBSERVING THE MOON

The Full Moon

The Moon is the brightest and largest object in the night sky so it is inevitable that it is usually the first thing a beginner to astronomy as a hobby will choose to observe. This is actually a good plan because it is the easiest target to find and has many interesting things to see. It is also a great target to use when familiarising ourselves with a new telescope and aligning the finder scope.

One of the great advantages of starting with observing the Moon is that it can be done using almost any telescope. One slight disadvantage is the Moon can be very bright especially when using a larger telescope to observe the full Moon or even half Moon. This is not a great problem because there are two ways to overcome this ‘minor problem'. We can use a Moon Filter to reduce the glare or we can fit a mask over the end of the telescope.

Many telescopes are supplied with a Dust Cap (that is used to cover the open tube and keep dust out). Most Dust Caps are supplied with a Moon Cap that can be removed from the Dust Cap to create a mask that will reduce the amount of light entering the tube. See below.

Dust Cap fitted

Moon Cap removed

There are two types of Moon Filter: a simple set darkening type that has a fixed light reducing glass. The second type is an adjustable Polaroid Moon Filter. This type has two Polaroid glasses that can be rotated to align or misalign the polarity of the two glasses. This filter has the ability to adjust the amount of light it allows to pass through the filter. Most types of filters can be attached to an eyepiece by screwing them into the thread on the eyepiece mounting barrel as shown below. The moon filter also improves the contrast of the image.

A Polaroid Moon Filter fitted to an eyepiece

Binoculars can be used to observe the Moon and will provide a good overview but they do only have a low magnification. A pair of binoculars will be marked with the ‘magnification' and ‘aperture' (diameter of the main lens) of the instrument in the form: 9x50. This example means the binocular has a magnification of 9 times and an aperture of 50mm. To see detail on the Moon surface needs a magnification of at least 25 to 30 times so it is obvious larger binoculars or a telescope is required.

A new telescope is usually supplied with two eyepieces. These are small microscopes that fit into the telescope focusing unit to magnify the image produced by the telescope. The eyepieces supplied are usually marked: 25mm and 10mm, this is the focal length. The lower the number the higher magnification the eyepiece will provide. The magnification of the Moon can be calculated by dividing the focal length of the telescope by the focal length of the eyepiece being used. For example Telescope focal length 1000mm and eyepiece focal length 10mm will produce: 1000 / 10 = 100x.

Observing should be started using a low power eyepiece (the 25mm) this will produce a magnification (based on the previous example) 1000 / 25 = 40x. This will provide a good overall view of the Moon. When a part of the Moon is selected for more detailed observation the eyepiece can be carefully replaced with the 10mm to increase the magnification to 100x. If further magnification is required and ‘seeing' conditions permit the Barlow Lens supplied can be used to double the magnification of each eyepiece. Fitting the Barlow will magnify the previous examples by 2x for example: (1000 / 10) x 2 = 200x but some trial and error is necessary.

Perhaps one of the first things to do to help explore the Moon is to obtain a Moon Chart. These can be obtained from most astronomy dealers and can be purchased on line. Books can also be purchased that will provide charts and detailed guidance about the interesting things to look for on the Moon. Another option is to use a computer application on a laptop. A good option is Virtual Moon Atlas that can be down loaded free.

The important thing about observing the Moon is to choose the best time to see feature to be studied. The reason for this is to do with the illumination of the surface of the Moon by the Sun. We know the Moon has phases caused by its movement around Earth on its monthly orbit. Each evening of the month we have a different view of the Moon and we see its shape change from a thin crescent to full Moon then a return to a thinner crescent after full Moon.

The phases of the Moon (Sun is off to the right)

In the diagram above the Sun is shining from the right. The inner Moon images demonstrate the orbit of the Moon around Earth and shows how the Moon is illuminated by the Sun. The outer Moon images show the view of the Moon as seen from Earth. From Earth the same side of the Moon is always facing us so the Moon appears not to rotate for us. However if viewed from the Sun the Moon can be seen orbiting around Earth and as it orbits it would appear to rotate once on every orbit. This means over the course of one orbit (about 29.5 days) the whole surface of the Moon will be illuminated at some time. Therefore for a given point on the Moon, a day will last for one half of the month and it will be night for the other rest of the month.

So the two Moon images on the right show the Moon positioned between the Sun and Earth. From Earth the dark side of the Moon is facing towards us so we cannot see it. As the Moon moves around its orbit some of the illuminated side begins to appear and we see the Moon as a New Moon (the growing crescent is called ‘waxing'). After about seven days the Moon would reach the lower middle point of its orbit and half of the illuminated side of the Moon is visible from Earth, this is called ‘First Quarter'. After a further seven days the Moon will have reached the left side of the diagram and the whole of the Moon facing Earth is illuminated so we call this the ‘Full Moon'.

A further seven days takes the Moon to the lower position on the diagram where the opposite side to the ‘First Quarter' is illuminated, we call this ‘Last Quarter'. The final phase (called waning) is rarely seen by people who sleep normal hours. This is because the Moon does not rise until after midnight in the east. The crescent becomes thinner as it draws closer to the Sun to start another New Moon.

The line between the light side (day) on the Moon and the dark side (night) is known as the ‘Terminator'. The Terminator after New Moon and up until Full Moon is the sunrise line and the terminator after Full Moon until New Moon is sunset on the Moon. On the terminator the Sun casts long shadows as it does on Earth at sunset. Shadows near the terminator give relief to the lunar terrain and produce an almost 3D perspective. So it is always best to observe an object when it is in the daylight near the Terminator.

Craters close to the Terminator

There are two ways of deciding what to observe on particular evening. The first is to check your Moon chart on the evening to see what is best placed, close to the terminator, at that time. If a computer generated chart is used a copy can be printed and used to identify all the things of interest on that observing session.

The other option is used when a particular feature is to be observed or studied in detail. On this occasion it might be better to use the chart to find which evenings would be best to see this feature. Depending on the particular feature it may be possible to predict two or three evenings when it is close to the terminator and good for observing. Using a Moon Filter can make looking at the Moon more comfortable and give the Moon more contrast to improve the view.

There are two types of Moon Filter: a simple set darkening type that has a fixed light reducing glass. The second type is an adjustable Polaroid Moon Filter. This type has two Polaroid glasses that can be rotated to align or misalign the polarity of the two glasses. This filter has the ability to adjust the amount of light it allows to pass through the filter. These types of filters can be attached to an eyepiece by screwing them into the thread on the eyepiece mounting barrel as shown above.

FEATURES ON THE MOON

 

A map of the Moon with Maria (Seas) and Craters labelled

With our unaided (naked) eyes we can see darker patches on the surface of the Moon . These are called ‘Maria' (Mare single ) the Latin word for Sea because they were mistakenly thought to be seas on the Moon. The Maria are particularly obvious on the Full Moon and are marked on the map above as Mare Serenitatis (Sea of Serenity) for example. Using binoculars will show the shapes of the Maria in more detail and also reveal the smaller dark areas that may be parts of larger seas or separate areas.

A telescope will reveal the Moon in a completely different view. Probably the most noticeable feature will be the thousands of large and small craters. It is interesting to distinguish the different types of craters and how they appear. Some large craters have a central mountain and often have terraced walls (Copernicus and Tycho). Some have smaller craters inside their walls that help to work out the sequence of how they were formed.

Some areas of the Moon are more cratered than others. There are large areas that have so many craters that there appear to be no smooth areas at all. Other areas, particularly Maria, have almost no craters.

There are also mountain ranges that are often named after mountain ranges on Earth. Many of these mountain ranges appear to be the walls of vast craters that have all but disappeared under ancient lava flows and the effect of later impacts. There are however some that do appear to be natural mountain ranges.

There are features known as ‘Rills' that appear to be gullies and creases or cliff faces caused by cracking of the surface as the Moon cooled billions of years ago.

Craters, Mountains and rills are best viewed when they are close to the ‘Terminator', the line between night and day. Here the shadows cast by the setting Sun cause long shadows that give relief and clarity to the view.

THE SOLAR SYSTEM - JUNE 2021

The planets at sunrise 05:00 on 19th June

The chart above shows the location of the planets relative to the Sun. The sky has been darkened to make the planets visible. The planets to the west of the Sun (right) will be visible in the early morning sky before sunrise. The planets to the east of the Sun (left) will be visible in the early evening sky after sunset.

MERCURY will be in the early morning sky as the Sun is rising. It will be very difficult to find in the bright sky and will require a lot of care to find and a clear view to the western horizon.

Mars and Venus in the early evening sky

VENUS will be visible in the early evening sky as soon as possible after sunset. It will be easy to find but will it require a clear view to the western horizon. Venus is emerging from its excursion behind the Sun when it was in ‘Conjunction' with the Sun. It will appear at its smallest diameter and will be fully illuminated because it is still beyond the Sun from our point of view.

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 4.0 arc-seconds as Earth pulls further away. Mars will be around until the end of June but will be moving closer to the south western horizon.

JUPITER will be rising in the east from about 00:30 and will be visible in the south east until sunrise. Jupiter will be at will be better positioned at its 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 east at about midnight. 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 very difficult to find in the brightening early morning sky and will need a telescope. This month it will rise in the south west at about 02:45.

NEPTUNE will be just visible this month to the east of Jupiter. It will be difficult to see in the brightening morning sky as it is only magnitude +7.8 and will need a telescope.

THE SUN

The Sun rises at about 04:45 at the beginning of the month and 04:50 at the end. It sets at 21:10 at the beginning of the month and 21:25 at the end of the month. It will reach its highest point in the sky at midday (13:00 BST) on 21st June at the Summer Solstice.

THE SUMMER SOLSTICE (Midsummer Day)

The Summer Solstice (Midsummer Day) 21st June

As astronomers we have a rather confusing view of the sky around us due to the tilt of Earth's axis. There are some very noticeable effects that we take for granted. The first is: how much the position of the Sun in the sky changes from summer to winter.

The chart above shows the sky at midday on Midsummer Day. The Sun appears at its highest point in the Sky on 21st June at 13:00 BST (12:00 GMT) so for the UK this the astronomical middle of summer. The Zenith is the point directly overhead from Newbury, England and is marked as a red cross on the chart above.

The Ecliptic (red arc) is the imaginary line that represents the equator of the Solar System. The Sun, Moon and planets appear to move along this imaginary line as Earth moves around its orbit about the Sun. As the tilt of Earth's axis always points to the same direction and towards the same point in the sky, the Ecliptic appears to rise and fall from our tilted point of view on Earth. See the diagram below.

During the summer months the Ecliptic appears high during the day so the Sun will be at its greatest height in the sky at midday. However during the summer nights the Ecliptic is low in the sky and we see the planets and Moon ‘hugging' the southern horizon. During the summer the Moon can look much larger when it is very close to the horizon and gives us the Super Moon effect. During the winter months the Ecliptic is high during the nights and low during the day so the Sun always looks very low in the sky during the winter days.

Earth is always tilted in the same direction

Another affect caused by the tilted Earth is that our sky appears to move up and down as Earth's Equator effectively moves up and down causing summer and winter.

The movement of Earth's Equator

Our summer occurs when the Equator moves up to the position of the Tropic of Cancer or down to The Tropic of Capricorn for winter. On 21st June the Equator will be at its highest position and it will be the Summer Solstice . Britain will be closest to the Equator on 21st June so the Sun will appear at its highest point of the year in the southern sky at midday.

There have been few small Sunspots during April and May.

 

Sunspots imaged by SOHO on 25th April

There will be a Partial Solar Eclipse on 10th June.

THE MOON PHASES DURING JUNE

Last Quarter will be on 2nd June

New Moon will be on 10th June (Solar Eclipse)

First Quarter will be on 18th June

Full Moon will be on 24th June

 

PARTIAL SOLAR ECLIPSE 10th JUNE 2021

Phases of the eclipse as seen from Newbury in the UK

On 10th June 2021 a Partial Solar Eclipse will be visible from the UK. From Newbury UK we will see about 20% of the Sun covered by the Moon at 11:13 BST. The cover will be greater further north as the eclipse begins in northern Canada then moves across Greenland and the North Pole and finishes over Siberia.

From these more northerly areas there will be an Annular Eclipse. An Annular Eclipse occurs because the Moon's orbit isn't entirely circular but elliptical so it moves closer and further from Earth. On 8th June 2021 the Moon reaches its furthest point from Earth on its orbit that we call ‘apogee'. Consequently the Moon will appear smaller in the sky than normal.

The Annular eclipse seen in 2019

The Moon will still be smaller on 10th June (the day of the eclipse) and will appear slightly smaller than the Sun so it will not completely cover the Sun. Therefore at the midpoint of the eclipse the outer edge of the Sun will be visible around the silhouette of the Moon. This is sometimes called the ‘Ring of Fire' effect. An Annular Solar Eclipse occurs when the Moon appears smaller than the Sun. Therefore we can see the bright outer edge of the Sun around the Moon that is sometimes called the ‘Ring of Fire'. The sky does not become fully dark like a regular Total Solar Eclipse.

Map showing Moon coverage over the Sun

From the south of the UK we will first see the edge of the Moon start to ‘cut' into the edge of the Sun at 10:06 this will be ‘First Contact'. At 11:13 we will see almost 20% of the Moon in front of the Sun so this will be the maximum of our eclipse. The Moon's silhouette will then begin to move off the Sun until it will have moved completely off the edge of the Sun at 12:24 and the Partial Eclipse will be over.

During the 10th June Partial Eclipse it will not become noticeably darker in the UK as happens during a total Eclipse. The remaining 80% of the Sun will still be bright and appear as normal daylight.

OBSERVING THE SOLAR ECLIPSE

We must remember it is very dangerous to look directly at the Sun without eye protection. Never stare directly at the Sun because it may cause permanent damage to the eyes.

The most important thing is to make sure we observe this eclipse safely. We must never stare at the Sun because it will damage our eyes.

The simplest way to do it is to use a pair of special Solar Viewing Spectacles. Regular sunglasses must not be used to look at the Sun they do not stop enough sunlight and heat.

These special Solar Viewing Spectacles can be bought from astronomy shops.

There are two ways to observe the Sun safely these are to use a special Solar Filter or to project an image of the Sun on to a screen. If we do have a telescope we can use a piece of white card as a screen and project the light from the Sun on to the card. The image of the Sun can also be projected on to a screen using binoculars.

A chair or small set of steps can be used to support a cardboard screen behind the binocular to project the image on to. The side of the binocular not being used must be covered.

To prevent damage to the binoculars a mask should be fitted to reduce the amount of heat entering the lens. This mask can be made out of cardboard with a 20 – 25mm hole to let the light through. It must be well secured over the lens.

It mBinoculars set up for projecting the image of the Sun on to a card.

A simple rig can be assembled to support a screen and attach it to a telescope to allow the image of the Sun to be projected on to a screen. The picture below shows such a homemade rig can be fitted to a refracting telescope.

A Solar Observing Screen attached to a telescope

For those who are fortunate to have access to a telescope, observing the Sun can be taken a step further. The telescope can be used to ‘safely' to observe the Sun in more detail. The telescope must be fitted with a fail-proof Solar Filter. This can be bought ready made from an astronomy shop or can be made at home using a sheet of special Mylar (plastic) Solar Film.

This type of filter removes the vast majority of the light and heat from the Sun to a safe level that will not damage the eye of the observer. The light available is the same ‘white' light that is naturally emitted by the Sun but greatly reduced in intensity .

The same telescope set up for solar observing using a Solar Filter

For more information, have a look at the ‘Solar Eclipse 10th June 2021' presentation in the PRESENTATIONS section, on the Beginners website.

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