The Andromeda Galaxy or MESSIER 31 (M31) is the closest large galaxy to the MILKY WAY. It is 2.5 million LIGHT-YEARS away and gets its name from the CONSTELLATION in which it appears in our night sky (see picture below). The single star that appears on the top left of the square making up the constellation of Pegasus is called Alpheratz. Although it is used to form the shape of the square it is now assigned exclusively to the constellation of Andromeda and not Pegasus.
However, before the modern constellation boundaries were defined in 1930, Alpheratz was considered to be part of both Andromeda and Pegasus. Around 270 BCE, the Greek poet Aratus designated the star as xunos aster, “joint star,” i.e. shared by Andromeda and Pegasus. The 2nd century CE Greek astronomer Ptolemy also considered the star to be shared by the two constellations. The German astronomer Johann Bayer (1572 – 1625) who assigned greek letters to the brightest stars in the constellations designated Alpheratz as Alpha Andromedae and Delta Pegasi.
Alpheratz kept its Pegasus membership into the 20th century, when the designation Delta Pegasi finally fell into disuse. Once the constellation boundaries were set, the star was assigned only to Andromeda.
The Andromeda Galaxy is one of the brightest Messier objects with an apparent MAGNITUDE of 3.4 and is the farthest object that can be seen with the unaided eye. We only see the very bright central region, if we could see the whole of the galaxy it would stretch 6 full Moon widths across the sky (3 degrees).
It is a spiral galaxy 260,000 light-years in diameter containing 1 trillion stars so over twice the size of our own Milky Way galaxy. It is the most massive of the galaxies in the LOCAL CLUSTER which contains the Milky Way, the Triangulum galaxy (M33) and 44 other smaller galaxies. It has a double nucleus with at least one supermassive BLACK HOLE hidden at its core. There are at least 450 GLOBULAR CLUSTERS orbiting around the galaxy and some of these are the most densely populated globulars ever seen.
The Andromeda Galaxy is approaching the Milky Way at approximately 100-140 km/s and in about 3.75 billion years the galaxies will collide, merging and evolving into a new type of galaxy, an ELLIPTICAL GALAXY or a LARGE DISC GALAXY.
M13 (The Andromeda Galaxy)
Arcturus can be found from the tail of the great bear Ursa Major (or the handle of the saucepan). If you follow the arc of these 4 stars to the next brightest star you will find Arcturus. You can easily remember this because you arc to Arcturus. It is the brightest star in the constellation Boötes the herdsman or bear keeper. In fact Arcturus is the fourth brightest star the night sky. It is also part of the asterism called the Spring Triangle which includes Spica in Virgo and Regulus in Leo (or Denebola in Leo).
When you find the star you should see that it looks an orange/red colour. This is because it is a red giant star. The colour is an indication of its surface temperature. Red stars are cooler than blue stars. It is 36.7 light years away from our Sun which is quite close relatively speaking. It is a lot older than our Sun at about 7.1 billion years old and although it is only 1.8 times the mass of our Sun, as an aging star it has expanded to over 25 times the diameter of our Sun. It is 170 times as luminous as our Sun and has a magnitude of -0.04.
Fun Facts about Arcturus
Finding Arcturus from the Plough. Clip from Stellarium.org
Many people think the stars are colourless, or all white, but if you venture outdoors on a cold winter night and look south you’ll see at least one star that is noticeably red. This is the star Betelgeuse, normally the ninth brightest star in the sky (but see Fun Facts below) and conspicuous as the left hand shoulder of the Orion constellation (the Hunter). Betelgeuse is bright partly because it’s relatively close to us (a mere 640 or so light years) and partly because it is very big and luminous (about 100,000 times more luminous than the Sun). The star is what we call a red supergiant, with a surface radius that would extend to the orbit of Jupiter if it was at the centre of our own solar system. That’s five times the distance of the earth to the Sun!
To find Betelgeuse, look above and to the right of the brightest star, Sirius, and above and left of the three stars in a line that make up Orion’s belt. But don’t hang about. Orion is fast dropping below the western horizon and if you don’t look soon after it gets dark now you may miss your chance until Autumn!
Although less than 10 million years old, Betelgeuse is a dying star. Its mass is 30 times that of our Sun and it’s fast consuming its hydrogen, such that it’s expected to explode as a supernova in the next million years or so. When it finally goes “pop” it will be the brightest star in the sky and even visible even in daytime. Its core will have fused carbon, neon, oxygen and then silicon until all that is left is a hyper-dense core - a rapidly spinning neutron star the size of a city but with a mass greater than that of the Sun!
No-one is really sure how to pronounce “Betelgeuse” because it derives from the Arabic “Ibt al Jauzah,” which is said to mean “the armpit of the central one” or “hand of al-Jauza" (Orion). The best guess is thought to be “bet-uhl-gurz” but it’s often pronounced in English as “beetle juice” which may not be accurate but is certainly fun!
Finding Betelgeuse (from Stellarium.org).
Capella, sometimes called the “Goat Star,” is the bright, golden star currently shining above Venus in the West after dusk. Just 42 light years away (very much a stellar neighbour), Capella is the brightest star in the constellation of Auriga (the Charioteer) and the sixth brightest in Earth’s skies. Using very large telescopes astronomers have discovered Capella is actually not one star but four!
Two of the stars are yellow giants, just under 10 times the diameter of the Sun and orbiting each other very closely. Despite their size they are only around 60 million miles apart, or about two-thirds the distance of Earth from the Sun. The surface temperature of these two stars is similar to the Sun’s, which is why Capella appears yellow in our sky. In fact, the Sun would appear similarly golden in the sky of a planet (if there were one!) orbiting Capella, although much fainter because of the Sun’s smaller size. In every other way, though, Capella’s stars are very different from our own. These giant stars have burnt up their hydrogen, expanded, and are well on their way to becoming cool, dying red giant stars.
The other two stars gravitationally part of the Capella system are about one light year away from the yellow giants and, although faint, can be seen with amateur telescopes. These are long-lived, red dwarf stars smaller and cooler than our sun, which are using up their hydrogen fuel at a much slower rate.
Capella’s other name of the “Goat Star” is thought to derive from an ancient association of the constellation of Auriga with a goatherd. It’s also why the three stars at the top right in Auriga are often called “The Kids.” Auriga is linked to the ancient Greek sea god Poseidon and the Roman god Neptune.
Fun Facts about Capella
You can find Capella by making a triangle with Betelgeuse and Aldebaran or you can find the distinctive W of Cassiopeia and draw an imaginary line from the W (see the picture below),
Finding Capella (from Stellarium.org)
The Hyades cluster of stars forms a relatively distinct V shape in the constellation Taurus. Astronomers call this type of cluster an open cluster. It is the nearest open cluster to the Sun at 153 light years away. Have a look at the astronomy glossary for an explanation of what a light year is. Even though you can’t see them with the unaided eye there are hundreds of stars in the cluster. They are all the same age, they were born in the same place, they share the same chemistry and they move through space together. However, there is one exception! The brightest star which is an orange/red colour isn’t actually in the cluster at all. It only looks like it is part of the cluster from where we are on Earth. This star is called Aldebaran and just happens to lie along the same line of sight as the stars in the Hyades cluster even though it is only half the distance to the cluster.
The V shape is the head of the bull, Taurus. The star Aldebaran represents the fiery red eye of the bull. Above the shoulder of the bull, hovering like a swarm of bees, is the open cluster Pleiades. In Greek mythology, the Hyades were the five daughters of Atlas and half-sisters to the Pleiades.
The stars in the Hyades cluster are estimated to be about 625 million years old; a lot older than the stars in the Pleiades cluster.
Finding the Hyades Cluster
The Hyades cluster is pretty easy to find and you will be able to look at it in the western sky after sunset during the first half of April. It will get a little lower in the night sky every night until it is no longer visible above the horizon.
From the constellation Orion
By using Orion’s Belt, a compact and noticeable line of three blue-white stars in the constellation Orion the Hunter. Draw a line westward (generally toward your sunset direction) through the Belt stars, and you will come to the bright reddish star Aldebaran, the Bull’s fiery red eye. You should then be able to make out the V shape of the Hyades cluster.
The V-shaped figure of stars (except Aldebaran) highlights the brightest of the Hyades’ few hundred stars. A dozen or more Hyades stars are visible to the unaided eye in a dark sky, but several dozen of the cluster’s stars can be resolved through binoculars or low power in a telescope.
By the middle of April Venus will form the top of a triangle with Hyades and Pleiades on the 2 points of the triangle’s base.
Clips taken from Stellarium.org
Jupiter reaches conjunction on the 11th April 2023 which means it lies on the opposite side of the Sun to Earth and is therefore behind the Sun and not visible at all. Dont be dismayed however, it will come back into our evening skies in the late summer/early Autumn reaching opposition on 3 November 2023. Opposition marks the middle of the time when you can see Jupiter the best. It will be a mere 593 million kilometres away from Earth (4 Astronomical Units). At this point, light from Jupiter takes just over 33 minutes to reach our eyes (it takes light 8.3 minutes to travel 1 AU). It is at its brightest around opposition at magnitude -2.8 and sticks out like a beacon.
If you want to spot Jupiter in late Spring/Summer then you need to be awake in the wee small hours so if you are a morning person you will be able to see it before dawn. For the rise times of Jupiter see Heavens Above.
In the late Summer and Autumn you will see this magnificient planet in the southern sky crossing from east to west throughout the early morning and eventually it will become an evening object rising just before midnight by the very end of July. It can be seen in the constellation Aries.
Find a spot with a flat horizon that is as uninterrupted by buildings and trees as possible. It will come to its closest point to Earth, due south at about midnight around the time of opposition but as the month progresses Jupiter will rise and set earlier each night. By the time it gets to late autumn Jupiter will be heading towards the western horizon when it gets dark. However, it will be visible in the evening sky for the rest of the year.
If you have a pair of binoculars then look for the largest moons of Jupiter – the Galilean moons. These are Io, Europa, Ganymede and Callisto. While Io is the closest and Callisto the furthest away from Jupiter they do not always appear in that order because they are orbiting around Jupiter at different speeds and at different distances. In fact they are not always just on one side of the planet. To find out which moon is where on the night you are viewing, look at the website In The Sky (https://in-the-sky.org/jupiter.php). Sometimes you may not be able to see all 4 moons. This is because of their orbital motion. Sometimes they will disappear behind the planet (occultation) and sometimes they will cross the face of the planet during a transit. If they are crossing in front of Jupiter then their shadow can be seen on the face of the planet if you have a telescope. Unfortunately it’s not so easy if not impossible to see a shadow with binoculars. The moons will pass behind the planet from west to east and in front of the planet from east to west.
While 10 x 50 binoculars are good to use if the magnification of your binoculars is not as much as 10 then still have a go. I have seen them clearly with 8 x 56 (56 means they do let in more light but they don’t magnify as much). You will find that Jupiter and the moons wobble about a lot so rest your arms on something solid. This could be a gate or even a friend!
Image courtesy NASA. The black dot is a shadow of the moon Europa
Another feature on Jupiter is the Great Red Spot which can be seen on the NASA image. It is a storm that has been raging for hundreds of years. You will need a telescope to see this though.
This year we are treated to a double planet experience with Jupiter rising closely behind Saturn. This is the opposite of what happened in 2020 when Jupiter rose in before Saturn, "caught up to" Saturn on the 21 December 2020 in a great conjunction, undertook it and now they are moving further apart from each other.
May 15 2022 at 4.30am; half and hour before sunrise. Taken from Stellarium.
September 26 at 1am; taken from Stellarium
There is an opposition of Mars every 2 years and 50 days when it will be at its brightest. However, because of the elliptical nature of the orbit of Mars the distance from Earth at each opposition is not always the same.
No matter how close or far away it always appears to be very red and is quite unmistakeable. The closer it is the redder it appears.
Image capture from Stellarium. End April at 04:30.
Image capture from Stellarium. Midnight 1 september.
December 8 2022 at midnight. Image captured from Stellarium
Mercury is a very elusive planet and more often than not quite close to the Sun so difficult to see. It is an evening object during the following months in 2023: mid March - April; end July into August; briefly in mid November/December. It is a morning object in 2023: towards end of May and into June; briefly in May; briefly end September/beginning October.
It is at Greatest Eastern Elongation: 11 April, 10 August & 4 December 2023; 24 March, 22 July & 16 November 2024. This is when it is at its greatest angular separation from the Sun and appears very bright. You do need a good clear sky without any light pollution and as clear a horizon as possible to see this elusive little planet.
Facts about Mercury
Mercury's spin-orbit resonance.
M13 is a deep sky object visible from Spring in the constellation of Hercules. It is a Messier object and that is where the M comes from. It wasn’t actually discovered by Charles Messier the comet hunter, it was discovered by Edmund Halley back in 1714. Find out more about Charles Messier and why he created a catalogue of deep sky objects.
M13 is actually a globular cluster. A glowing ball of some hundreds of thousands of stars all held together by gravity. It is just on the edge of being visible with the unaided eye at magnitude 5.8 but unless you have really good eyesight and an extremely clear night it is very difficult to spot without binoculars or a telescope. However, if you know where to look and have a pair of binoculars it should be quite easy to see and looks like a fuzzy patch of light. You won’t be able to spot individual stars unless you have a telescope (even a relatively small telescope may resolve stars in the outer regions of the cluster) but then again you are looking at something that is 22,000-25,000 light years away! Have a look at the image to find out where in the constellation M13 is located. The body of Hercules is represented by 4 stars that make up the shape of a keystone.
It is about 145 light years in diameter and through a telescope looks like a glowing 3 dimensional ball of stars.
Fun facts about M13
To find out why a full Moon occurs look in the Astronomy Glossary to learn more about the phases of the Moon.
Full Moon Calendar for 2023. There are 2 'Supermoons' this year (highlighted in bold type) and 2 other close Moons which by some definitions are also 'Supermoons.' There are actually 13 Full Moons in 2023.
|6 January||3 July Supermoon|
|5 February||1 August Supermoon|
|7 March||31 August Blue Moon & Supermoon|
|6 April||29 September Supermoon|
|5 May||28 October|
|4 June||27 November|
The July and September Supermoons in 2023 have again thrown up some confusion about what the definition of a supermoon actually is. So what is a ‘Supermoon’ and why do experts disagree about what constitutes a ‘Supermoon?’
What is a ‘Supermoon’
The orbit of the moon around Earth is elliptical (see diagram below). You will notice that the closest point is called perigee and the furthest point is called apogee. ‘Supermoons’ occur when the full or new Moon coincides or is close to perigee. Of course the Moon isn’t actually any larger than normal it just looks larger because it is closer to us. If you measured the angular diameter between the full Moon at perigee and the full Moon at apogee there would be a 14% difference. Also because it is closer it is brighter. A full Moon at perigee is 30% brighter than a full Moon at apogee. You cannot really see a huge difference between full Moons. You can often get the illusion it is bigger when it rises over the horizon and you compare it with things like trees or buildings on the horizon. So why the disagreement? It’s all in the definition!
What is the definition of a ‘Supermoon’
First of all it is important to say that ‘Supermoon’ is not an official astronomical term and there are differences in the way the term is interpreted. In fact The International Astronomical Union (IAU) who are responsible for naming and defining things in astronomy have not actually recognised the term ‘Supermoon.’
Originally it was an astrologer called Richard Nolle in 1979 who coined the term ‘Supermoon.’ He defined a ‘Supermoon’ as a full or new Moon which comes within 90% of its closest approach to Earth (perigee). So what does that mean?
The average closest approach is about 362,600 km but the range is between 356,500 and 370,400 km. Each orbit of the Moon around the Earth has a slightly different perigee and apogee distance.
So why do people sometimes disagree?
You can determine whether or not the full Moons in any given year are ‘Supermoons’ two different ways:
1. Calculating the difference between the year’s furthest distance (apogee) and the year’s closest distance (perigee) and taking that number to calculate the maximum distance from Earth when a full moon can be classed as a ‘Supermoon.’ Note: Furthest apogee and closest perigee may be new moons or full moons.
This is what is happening this year (2023):
August 16 2023 furthest apogee: 406,634 km (New Moon)
January 21 2023 closest perigee: 356,569 km (New Moon)
Difference: 50,065 km.
90% of the difference = 45,059 km.
Apogee – 90% of difference (406,634 – 45,059) = 361,575 km so any full Moon coming closer than this would be classed as a ‘Supermoon’ in 2023.
2. Calculating the distance of the full Moon relative to the apogees and perigees in 2023 (July and September Full Moons only).
June 22, 2023 apogee: 405,385 km
July 4, 2023 perigee: 360,149 km
Difference: 45,236 km
July 3, 2023 full moon: 361,934 km
Difference: 405,358 – 361,934 = 43,424 km
43,424 / 45,236 x 100 = 95.9%
September 12, 2023 apogee: 406,291 km
September 28, 2023 perigee: 359,911 km
Difference: 46,380 km
September 29 full Moon: 361,552 km
Difference: 406,291 – 361,552 = 44,739 km
44,739 /46,380 x 100 = 96.5%
So what does this show?
|Date of Full Moon||Distance km||Definition 1||Definition 2|
|July 3 2023||361,934||NOT Supermoon||Supermoon|
|August 1 2023||357,530||Supermoon||Supermoon|
|August 31 2023||357,344||Supermoon||Supermoon|
|September 29 2023||361,552||Supermoon||Supermoon|
To make matters even more complicated! Simpler definitions by Sky & Telescope (Supermoons are within 358,884 Km of Earth) and Time and Date (Supermoons are within 360,000) Km of Earth then only the Full Moons of August are Supermoons.
Take your choice!
What’s in a name?
Full Moons are often named. This is especially true for Native Americans who tracked the changing seasons by the lunar month rather than the solar year. Here is a list of full Moon names for the year.
|Full Moon Month||Native American Name||Other Names|
|January||Wolf Moon||Moon afer Yule; Old Moon; Ice Moon; Snow Moon|
|February||Snow Moon||Hunger Moon; Storm Moon|
|March||Worm Moon (Earth worms coming out at the end of winter)||Crow Moon; Crust Moon; sap Moon; Sugar Moon; Chaste Moon; Lentern Moon|
|April||Pink Moon (from the pink of the emerging Phlox flowers)||Sprouting Grass Moon; Fish Moon; Hare Moon; Egg Moon; Paschal Moon|
|May||Flower Moon||Corn Planting moon; Milk Moon|
|June||Strawberry Moon||Hot Moon; Mead on; Rose Moon|
|July||Buck Moon||Thunder Moon; Wort Moon; Hay Moon|
|August||Sturgeon Moon||Green Corn Moon; Barley Moon; Fruit Mon; Grain Moon|
|September||Harvest Moon* or Corn Moon||Harvest Moon*; Full Corn Moon; Barley Moon|
|October||Hunter’s Moon||Ying Grass Moon; Blood Moon**; Sanguine Moon|
|November||Beaver Moon||Moon; Oak Moon|
|December||Cold Moon||Moon before Yule|
*Technically, the Harvest Moon is the Full Moon closest to the September equinox around September 22. Most years it is in September, but around every three years, it is in October. The Harvest Moon is the only Full Moon name which is determined by the equinox rather than a month.
** this should not be confused with a total eclipse of the Moon
The Orion Nebula is also known as M42. The M refers to Charles Messier an 18th century French astronomer and comet hunter. He compiled a list of deep sky fuzzy looking objects so they would not be mistaken for comets. Not all Messier objects were actually discovered by Charles Messier himself.
Nebula (plural nebulae) is Latin for mist and they are vast areas of cloud and dust between the stars. The Orion Nebula is so huge it is visible to the naked eye even though it is 1,344 light years away. It appears to cover 1 degree of the sky, an area twice the size of the full Moon, it is actually 24 light years across. A light year is roughly equivalent to 9.5 million million Km! It is a region where new stars are formed. These new stars at the centre of the dust cloud light up the surrounding gas making it visible through a telescope.
The Orion Nebula is in the constellation of Orion, which is a very prominent constellation in the winter sky. The nebula is located in the "sword" of Orion which hangs below the 3 stars that depict his belt (see diagram on right)
One of the new stars at the centre of the Orion Nebula is Theta-1 Orionis. It is easy to understand why it is called the Trapezium because, through the telescope, you should see 4 prominent stars in the shape of a trapezium (see Diagram below).
This false colour mosaic was made by combining several exposures from the Hubble Space Telescope Image credit: NASA Picture of the day
Where can you find a large family group in self-isolation in the sky? The answer is the Pleiades, otherwise known as the Seven Sisters. This little group of stars really is a group of siblings. It’s what astronomers call an open cluster. This is a cluster of stars that were formed at a similar time (by astronomers’ standards - we aren’t talking minutes here, or even years), from the same cloud of dust and gas. This means they all have a similar chemistry and a similar age - a mere 100 million years or so – not that old as stars go.
Like many families, sibling stars in open clusters tend to drift off to different places with time but the Pleiades won’t be noticeably changing in our lifetime. The current estimate is that it could take around 250 million years for this to happen. Looking at this group in binoculars or a small telescope, shows lots of stars in the group but with the unaided eye it’s not possible to see as many. The story goes that the ancient Greek army used to use them as an eye test. You had good enough eyesight if you could see at least 7 of the stars.
In some photographs of the Pleiades or in large amateur telescopes, you can see dust clouds (nebulosity) around them but don’t be tempted to think this is the cloud they were formed from. The cluster just happens to be passing through at the moment. The stars light up the dust to make a reflection nebula, which can be seen as the blue wispy bits in the photograph.
The Sun would have been formed in an open cluster like this and had sibling stars but they have long since drifted apart. Astronomers got very excited a while ago when they found a star so similar to the sun that they believed it could be one of the Sun’s siblings.
Image courtesy of Verity Stannard
Finding the Pleiades
The tiny, sparkly cluster of the Pleiades is easy to find in the early evening during the first half of April 2020. Right now it is just above the bright planet Venus. Venus will get closer and closer, until it actually looks as though it is in the cluster on 3rd April 2020 and will then move off upwards and to the left. The Pleiades will be a little lower in the sky each night as darkness falls until, by the very end of the month, they will be below the horizon and not possible to see.
To find the Pleiades in the night sky, first find something you know, maybe the Plough (Big Dipper) or Orion’s Belt.
From Orion’s Belt
From Orion’s belt, imagine a line stretching off to the right and it will point almost directly towards the Pleiades.
From the Plough
Instead of using the pointer stars that point towards the North Star, use the top two stars of the Plough’s box. You will need to follow an imaginary line from here to the right, right across the sky, through the bright star Capella and on to the Pleiades.
Clips taken from Stellarium.org
Pleiades from Orion
Pleiades from the Plough
Polaris is also called the Pole Star or the North Star. You can always see it in our night sky whatever time of the night or whatever time of the year. In fact it is even there in the day time we just cannot see it because the Sun (our star) is so bright it washes out all the other stars.
Polaris is in the constellation Ursa Minor (the little bear). It is a very important star especially for navigation because the axis of Earth is approximately aligned to the star. What does that mean? If you were able to draw a line from the North Pole straight up into space it would point to Polaris (well almost!). The line represents the Earth’s axis. The Earth spins around its axis once every day and because the axis pretty much lines up with Polaris then this is the only star in the northern hemisphere sky that doesn’t appear to move over the period of the night. Everything else appears to move around it because the earth is spinning. So Polaris tells you where north is.
Another important thing about Polaris for celestial navigation (finding your way around using the stars to guide you) is that it can tell you your latitude. The angle that Polaris makes with the horizon is your latitude north of the equator. If you were standing on the North Pole, Polaris would be right above your head. If you were at the equator Polaris would be in line with the horizon. The equator has a latitude of 0 degrees and the North Pole is at latitude 90 degrees north.
Polaris has not always been the Pole Star (North Star) and it won’t be the Pole Star forever. Even though it will still be called Polaris because that is its designated name, it won’t always point to the north celestial pole. Over a period of 26,000 years the Earth wobbles on its axis a bit like a gyroscope. This is called precession. Have a look at the astronomy glossary for an explanation of precession.
This beautiful image was taken by Verity Stannard who is a member of staff at The Observatory Science Centre.
Facts about Polaris
You will need to be able to locate the plough in the constellation of Ursa Major. Look at the map below. It also looks like a saucepan.
The 2 stars at the edge of the pan are called Merak and Dubhe. Draw an imaginary line from Merak, through Dubhe and keep going until you come to the next nearest bright star; this is Polaris.
It is about 25 degrees away from Dubhe. If you spread out your hand with your fingers as wide as they can go and then hold your hand up to the sky at arms-length then the distance between your thumb and little finger is about 25 degrees (this obviously depends on how big your hand is! It is based on an average adult hand).
Clips taken from Stellarium.org
Finding Polaris from the Plough
Merak and Dubhe point to Polaris
Regulus is one of two conspicuous stars (the other, brighter one, is Arcturus) in the Spring southern sky just after dark. Unlike the bright orange ember of Arcturus, Regulus is a fierce blue-white colour, which tells astronomers it’s a lot hotter!
It’s easy to find Regulus, as it provides the dot at the bottom of the reverse question mark that is the head and forequarters of Leo, the constellation of the lion. Dubbed “Heart of the Lion” (or Qalb al-Asad) by ancient arab astronomers, Regulus is about 79 light years from us, so relatively local. Its main star, Regulus A (like most stars, it’s yet another multiple star system) is more than twice as hot as the Sun at 12,190 degrees C. In fact, Regulus A beats the Sun on just about every metric. It’s almost four times the Sun’s mass, three times as wide and about 288 times brighter!
Like the Sun, though, Regulus is a “main sequence” middle-aged star, which means it still gains its energy by fusing hydrogen, the lightest element, into helium. Regulus A also has, like many of us middle-aged, a fat midriff, though this is due to its spin rather than to extra portions of cake. The star spins very fast on its axis, rotating once in just 16 hours. This makes it bulge outward, so it’s not so much spherical as egg-shaped.
Regulus A’s companions are two red dwarfs (much fainter, cooler and smaller stars) at around 4,200 times the distance between Earth and the Sun away. There is thought to be a fainter companion, the dying ember of a star with the Sun’s mass but only about the size of the Earth. Astronomers call these stars white dwarfs, and it’s how the Sun will end its life in about 4-5 billion years.
Finding Regulus from the Plough (from Stellarium.org) at sunset mid-May.
Saturn is the second largest planet in our solar system. It is at conjunction on the 16 February 2023 which means it lies on the opposite side of the Sun to the Earth. It is behind the Sun at this time from our line of sigt on Earth and is therefore not visible. However, like Jupiter it will be in our evening skies again in summer and is at opposition on 27 August 2023. Oppositions of Saturn occur every year but about 2 weeks later than the previous year. The farther a planet is from the Sun, the shorter the period of time between successive oppositions.
If you want to spot Saturn in Spring then you need to be awake in the wee small hours so if you are a morning person you will be able to see it before dawn. For the rise times of Saturn see Heavens Above.
At oposition, Saturn will rise above the eastern horizon as the Sun is setting below the western horizon so you will see it all night long. Opposition marks the middle of the time when you can see Saturn at its best because around this time it appears bigger and brighter. At opposition it will be about 1.33 billion kilometres away from Earth (8.9 Astronomical Units). When close to Earth like this it takes light from Saturn about 1 hour 15 minutes to reach our eyes. It is at its brightest around opposition at magnitude 0.2.
You will see it in the southern sky crossing from east to west throughout the night. It will lie in the constellation Aquarius the water bearer.
Saturn will only rise to about 28 degrees at opposition so find a spot with a flat horizon that is as uninterrupted by buildings and trees as possible. It will come to its highest point due south at about 1am around the time of opposition but as the month progresses Saturn will rise and set earlier each night.
Saturn has the most beautiful of all the ring systems in our solar system. During this opposition they will be tilted about 8.1 degrees to our line of sight and we are looking at the northern hemisphere at the moment. Maximum tilt is around 27 degrees, so they are closing up now to our line of site. They will be edge on to our line of site in 2025. It is very difficult if not impossible to see the rings through a pair of binoculars especially if they are only a modest magnification such as 10 times but don’t be put off having a go you may see that Saturn is a bit elongated. However, you need to hold your binoculars very steadily. Larger magnification means the binoculars tend to be heavier and even more prone to wobble so you will need a tripod or better still a telescope.
Image courtesy NASA
Sirius is not only the brightest star in the Canis Majoris (the Great Dog) constellation, but the brightest in the entire sky! Sometimes called the “the dog star,” Sirius is also one of the closest stars to us at a distance of just 8.6 light years. For comparison, the Sun is just 8 light minutes from Earth and our nearest star is 4.2 light years away.
Sirius is a winter star and is now approaching the beginning of its season in the northern hemisphere. It rises in the east: mid November at about 11.30pm; end of November approximately 10pm; mid December approximately 8.45pm; end December approximately 7.45pm. You can easily find it after it has risen and cleared the horizon and any obstacles such as trees etc. It is a bright beacon and when it is low in the sky you should see a number of colours as the light from this fairly nearby star travels through the atmosphere which is thicker on the horizon. As the light enters and travels through the atmosphere it is refracted splitting the white light into a rainbow of colours. This refraction is what makes stars twinkle (stellar scintillation).
If you know the constellation of Orion (the Hunter), just follow the line made by the three stars of his belt down to the left and you’ll find Sirius. You can’t miss it! Sirius is easily seen with the naked eye.
Sirius has been a familiar sight in the sky for thousands of years. The ancient Egyptians associated it with the god Osiris, and its appearance ahead of the sun in the early morning heralded the flooding of the Nile river and Egypt’s season of fertility and growth.
Although Sirius looks like just one bright star, it’s really two stars orbiting each other. The brightest, Sirius A is twice as massive as the Sun and 25 times more luminous. The fainter star, Sirius B (sometimes called “the pup”), is much smaller and orbits Sirius A about once every 50 years. Sirius B was once a much more massive star, bigger even than Sirius A, but consumed all its hydrogen and collapsed into what astronomers call a white dwarf star around 120 million years ago. It’s now even smaller than the Earth, but with about the same mass as the Sun!
Fun Facts about Sirius
Image taken from Stellarium.
At the beginning of January 2023 Venus is a bright early evening object and remains an evening object, setting later and later each evening until the end of May. It reaches greatest easten elongation on 4 June 2023 when it is the best time to observe the planet before it then starts to disappear in July. It is sometimes called the evening or morning star even though it is not a star at all.
As the Earth rotates on its axis Venus will appear to 'move' westwards. During the morning apparitions it appears in the east and the Sun rises behind it and during the evening apparitions it appears in the west and follows the Sun.
Venus is extremely bright because of where it is in its orbit around the Sun compared to where Earth is. On the 23 October 2023 it will at greatest western elongation and the best time to see it in the morning. Look at our glossary for an explanation of greatest eastern and western elongation.
How bright an object appears in the night sky is called its magnitude (again have a look at the glossary for an explanation). We can see things with the unaided eye that are as dim as magnitude 6. Venus at its brightest is -4.5 which is nearly 10,000 times brighter than the dimmest thing we can see without using binoculars or a telescope (magnitude 6).
Facts about Venus:
One hour before sunrise. Taken from Stellarium.