Archive for the ‘Constellations’ Category

17 June 2012

Woke up this morning and looked out of Bedroom Observatory. There was the crescent Moon hanging off the palm tree like a slice of silver fruit!

Crescent Moon

Crescent Moon (Click on image to enlarge)

I moved to get a better view and two bright sparks came into view! Jupiter and Venus! Gorgeous! And all before sunrise!
How quickly Venus has moved across!

Crescent Moon with Jupiter and Venus

Crescent Moon with Jupiter and Venus (Click on image to enlarge)

18 June 2012

We are really out of practice of waking at 4 AM and throwing off the feather doona, our warm nest for the night.  But jump out of bed we did, and looked out of Bedroom Observatory.  The sky overhead was clear, but it was too dark to judge whether there were low clouds in the eastern horizon.  A clear horizon was crucial for today’s pre-dawn viewing.  The only way to find the answer was to check from Clifftop Observatory.  So we had a quick cuppa, rugged up, gathered our camera gear, and drove to North Bondi.  The temperature was 9 deg C, and a cold wind from the south pole was about.  From where we parked we had to climb about 100 metres, and our fingers froze holding the cold metal of the camera tripod.

When we reached Clifftop Observatory, we stood stunned, breathless and motionless.   Jupiter was lined up with the Pleiades; the new moon was below lined up with Venus.  And Venus was pretending to be the brightest object in Taurus!

Jupiter, the Moon, Venus

As the sky brightened, some of the little stars got swallowed up in the dawn light, but the main players were still there, keeping us riveted.

Jupiter, the Moon and Venus

Jupiter, the Moon and Venus (Click on image to enlarge)

Before we left, a photo with our favourite tree and my favourite man was mandatory!

Dom the tree and the planets

Dom the tree and the planets (Click on the image to enlarge)

When we came home, we could still see the triangle of Jupiter, Moon and Venus over the roof of our house. 

Final look at Jupiter, the Moon and Venus

Final look at Jupiter, the Moon and Venus (Click on image to enlarge)

The weather man says the rain has gone to Spain for a few days.  So here’s cheers to clear weather and more good viewing.

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3 May 2012

Since we wrote the last blog, we have joined a Star Hoppers group led by our US mentor Greg. Most of the members are on the east coast of the US. We are the only two, as far as I know, Down Under. The aim of the group is to apply the classic advice of Sherlock Holmes – learn to “observe,” not simply to “see.”

And what should we observe in the first two weeks of May?

 “Good targets for viewing under dark skies are the Beehive (with binoculars or a low power scope), several double stars in Cancer and Leo or the galaxies in Leo.”  

We have to pick 3 – 5 targets on any given night.

The targets for May are fortunately also in constellations in our southern sky.

Constellations of Cancer and Leo

Stellarium image of constellations of Cancer and Leo (click on image to enlarge)

Waiting, waiting

Primed and ready – we waited for the weather to give us a break.

When weather reports of the last few months promised clear skies, they often didn’t mention the evening clouds that creep in, uninvited, and destroy any chance of viewing the stars.  So we’ve invented a new game to amuse ourselves: it’s called “Wither goes the weather?”

On the evening of the 3rd May, around 8 pm, we were pleasantly surprised to find the sky was clear of pesky clouds. When we walked out on to car deck observatory the panorama was breath-taking even with lights on everywhere and moonlight bathing the street. And the air was cool and calm. Perfect for viewing!

Dish of the sky

Stellarium image: Dish of the sky (click on image to enlarge)

Sure our view wasn’t quite as detailed as this, but with all those fairly large objects in view, we were very excited.

Starting from north – Mars was pretending to be one of the stars of Leo, forming a neat triangle with Regulus and Algieba.

Moving past the fat Gibbous Moon, and going east was Saturn, a golden brooch on the skirt of Virgo.

Looking south over Francis Street were the Pointers doing their job of showing us the Southern Cross.

Southern Cross and Pointers

A slide along the Milky Way and we were looking west at Canis Major (Big Dog) lying on his back wearing Sirius like a trophy on his chest. And caught in the moonlight (or should I say despite the moonlight) a hare, Lepus, being chased by the Big Dog. What a beautiful constellation this is! A neat curve of stars.

Just below the Big Dog is his master Orion slipping down sideways behind the trees!

View of western sky

Our photo: View of western sky (Click on image to enlarge

Spoilt for choice

How to choose three targets? Spoilt for choice, weren’t we? So we did what one does at a smorgasbord crammed with too many delectable dishes. We decided for our first night of star hopping to sample every big star and planet we could see and look for doubles and galaxies and clusters before we committed ourselves to three.

 Using our binoculars we star-and-planet hopped. With the Moon between Leo and Virgo, we were lucky to see Regulus and Algieba, but swinging to the Cross we saw the Jewel Box displaying its contents near Beta Crucis. And in the vicinity was the king of globular clusters – Omega Centaurus.

Going down the Milky Way, watered down by the light of the Moon and the lights on in every home in Francis street (people don’t believe in curtains or blinds), we looked for M41 in Canis Major, and found it rather faint. Caught M42 in Orion’s sword just before the Hunter slipped off on his perpetual chase of the Scorpion.

With the sky still clear at 8.30 pm we decided it was time to bring out the scope and look at the planets. Mars was a nice round reddish disk, but Saturn, despite the light of the Moon, beat the god of war in the beauty stakes. Saturn is certainly the pin-up boy of the planets! We could just see its moon, Titan; the other moons were drowned out by the light of the Moon.

Had we been able to see them, this is what we would have seen.

Saturn with moons

We’ll keep that treat for another night.

Turning our sights to the Moon

Having had our fill of stars and planets we turned the scope with the 6mm eyepiece on the Moon. OMG! The angle of the light from the sun lit up craters and mares perfectly, casting shadows to show them in 3D. We have never seen crater Aristarchus with Vallis Schroteri and  crater Herodotus  in such good light. It was the feature of the night.

Some features of the Moon

Another striking feature in this light was the Bay of Rainbows with crater Bianchini clearly visible as were the other four or five craters in the neighbourhood. And then looking toward the edge of the Moon was a rather angular crater with a prominent peak. I think it is Babbage, or perhaps Pythagoras.

We could even see the Rectii range, an unusually straight range in the Sea of Showers.

Blindingly brilliant were Copernicus, Kepler and up at the top Tycho. But another crater that stood out very clearly, so that we could even discern where its rim is broken, was Gassendi on Mare Humorum. With Gassendi A, this crater looks like an engagement ring with a big diamond.

After a month’s starvation of night sky viewing, we feasted on this evening’s gifts of a clear and still night.  An hour and a half of uninterrupted viewing was more than we hoped for, so when the clouds came over at 9.30 pm, we folded our scope without a word of complaint.

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Our friend Joe wrote, “I did notice the other night the Cross was clearly visible, but then I couldn’t locate Orion, which is usually near enough to Orion.”

So where is the Cross and where is Orion?  I was optimistic I’d be able to answer this question on 15 February, a glorious blue, sizzling summer’s day, followed by a clear night. 

For us, living in Sydney, the Southern Cross is always in the sky. From our perspective, it completes a full circle around the South Celestial Pole every 24 hours. We can’t of course see it in the day time, and even at night its ideal position may be at some awkward hour. Being able to spot it instantly depends on the time of night.

 In the summer months it is a question of waiting till the sky is dark enough and so at about 9 pm, I went out on to the street. It was roughly an hour after sunset and the Cross was visible east of south, between 20° and 30° above the horizon.

Southern Cross

Image from Stellarium: Southern Cross (Click on image to enlarge)

So where is it on its circular path around the South Celestial Pole? To answer this I need to understand our position on Earth and our view of the stars.

The Celestial Sphere

I consulted Stellarium and here’s where I found things getting a little complex. We live on a big ball, the Earth. And to mark where we live, geographers have drawn a grid of imaginary lines which they call the parallels of Latitude and the meridians of Longitude. These help us get a fix on where exactly we are on the Earth.

When we look up at the sky we see the sun, moon, planets and stars. To work out where these are, astronomers also draw a grid of imaginary lines. They pretend the sky is a big sphere – a Celestial Sphere around the Earth.

Celestial Sphere

Celestial Sphere (Click on image to enlarge)

The Celestial Sphere has a grid of imaginary lines similar to the ones on Earth. The imaginary lines are projected upward from those of the Earth, so that above the Earth’s equator is the celestial equator; and above Earth’s poles are the celestial poles. All objects in the sky are shown on the Celestial Sphere. We have to pretend the stars are fixed, while the planets, sun and moon move around.

Celestial Sphere

Celestial Sphere (Click on image to enlarge)


 I realise the Celestial Sphere is a very practical tool for us when we talk about the position of any celestial object.

Southern Cross on Celestial Sphere

The image below (from Stellarium) shows where the Southern Cross is on the Celestial Sphere. It is straddling the -60° circle of the grid; the Pointers cycle along following the same circle of celestial latitude.

Southern Cross on the Celestial Sphere

Southern Cross on the Celestial Sphere (Click on image to enlarge)

Why minus? I cast my mind back to my school days…  I remember the globe of the earth in the geography room.  I recall how the lines of latitude and longitude are numbered. 

Grid lines

The lines of latitude are circles. At the equator, the circle is 0°. Every ten degrees up a circle is drawn. In the northern hemisphere the 80° circle is near the arctic. The 90° circle is a point – the North Pole.

How latitude is drawn

How latitude is drawn (Click on image to enlarge)

From the equator, the southern hemisphere has the same numbering. To distinguish them we call them north and south latitudes.

Just as on Earth we have north latitude and south latitude, the Celestial Sphere has +(plus) for north and –(minus) for southern celestial latitudes.

There’s another difference. While the heavens above have exactly the same latitude and longitude as the earth below, the naming convention is different.  The celestial latitude is called declination and is measured in degrees.  The celestial longitude is called right ascension, and is measured in hours.

Lines of Declination and Right Ascension on the Celestial Sphere

Lines of Declination and Right Ascension on the Celestial Sphere (Click on image to enlarge)

Declination is like latitude projected on the Celestial Sphere.

Right Ascension is like longitude projected on the Celestial Sphere.

Where we live on our ball, the Earth, determines what we see in the Celestial Sphere. I’m going to take a little journey to see what I can see.

Travelling south

In the unlikely event that I’d be intrepid enough to go to the South Pole during the southern winter, I’m trying to imagine which stars I would see there.

The skies would be dark for most of the 24 hours. I’d see half the sky all the time and nothing would rise or set – all would simply revolve around me. When I look at Orion which straddles the Celestial Equator, I’d see half of the constellation that is south of the equator because it would never set. The half of Orion to the north of the equator would never rise.

Here’s an image from Stellarium which shows what is visible from the South Pole on the 21 June  – our winter solstice in the southern hemisphere. The sky is dark, the sun does not rise.  The sky is stars, stars, stars all 24 hours! Lie back and enjoy the view!

View from the South Pole

View from the South Pole at Summer Solstice (Click on image to enlarge)

 Travelling north

I decide to leave the icy wilderness and start sailing towards the equator. Each night that I move away from the pole a portion of the sky falls out of sight – sort of behind the hill.  More and more stars appear to rise and set, rather than go round and round. When I reach Sydney, which is on approximately 34°S latitude, the area of the sky between the -60° circle and the South Celestial Pole is visible 24 hours a day. Of course I see the stars only at night time.

I see diminishingly less of the southern skies as I travel towards the equator.  So from Darwin I’d see less of the southern skies than I do from Sydney.  The Cross would be much lower on the horizon, and wouldn’t be circumpolar; it would rise and set. 

And when I get to the equator every star on both sides of the Equator – even the North Star which is not really right on the pole, but off by almost a degree – will appear to rise and set. 

It’s quite a journey, but I’m beginning to appreciate what living on a ball, inside a sphere is like. Fascinating!

So, after that diversion, which helped me form a clearer picture of what we see and why, I return to the problem I started out with.

Which way to Orion?

Once I locate the Southern Cross, I travel across the sky towards the north and there Orion is, almost overhead.

Southern Cross and Orion

Image from Stellarium: Southern Cross and Orion (Click on image to enlarge)


In February, Orion rises in the east rather early – about 4 pm. So at 9 pm, he is overhead i.e. nearly 60° above the horizon. A big chunk of the Milky Way lies between Orion and the Southern Cross.

Which way to Orion from the Southern Cross?

Which way to Orion from the Southern Cross? (Click on image to enlarge)

If we look at the positions of Orion and the Southern Cross on the Celestial Sphere, we can see how far apart they are. Orion on 0° parallel and the Southern Cross on -60° parallel; roughly 2/3rds of the dome is between them. Here’s a sky map from Stellarium of them with grid.

Southern Cross and Orion on the Celestial Sphere

Southern Cross and Orion on the Celestial Sphere (Click on image to enlarge)

Now here’s a puzzle! If I were at the South Pole in deep summer, would I see Orion?

No, because in deep summer, the sun does not set at the Antarctic Circle – no dark night sky – no stars!

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5 February 2012

“The sun is shining — come on, be happy”— is the song on the lips of Sydneysiders! After weeks of rain and grey skies, the sun broke through on Saturday 4 February. The weatherman announced on Friday that we were in for another 21 days of rain with three sunny days between — and we were using up two of those three days on the weekend!

So we got the cameras charged and loaded, ready to click, day and night!

After a Sydney blue day, we awaited sunset. The Moon had risen and looked splendid as the Belt of Venus and the shadow of earth painted broad pink and blue bands across the eastern sky.

After dinner at my brother’s place in North Sydney, we went to the balcony at about 10 pm. Sydney harbour lights were doing their utmost to pollute the sky, but we’ve learnt to live with such annoyances. Tonight the lights did us a favour by blotting out the dimmer stars and allowing the Southern Cross to shine through in its full glory. The Pointers, α(Alpha) Centauri and β(Beta) Centauri, were low in the sky, doing their duty of pointing to the Southern Cross!  Oh, it was a grandstand view of the most recognizable constellation in Australia!

Southern Cross

Southern Cross (click on image to enlarge)

Our clever camera picked out all five stars of Crucis, the Southern Cross, the smallest and most distinctive of the 88 constellations that populate the sky. The Pointers and Crucis form a wonderful starting point for a study of the stars because of their position and colours. The Pointers and the Southern Cross

α(Alpha) Centauri and β(Beta) Centauri

We were marvelling at their colours – αCentauri’s yellow/red and βCentauri’s white when Dom says, “Did you know that αCentauri is the star closest to our galaxy?” 

“Of course I do, but did you know that it isn’t one star, but three?”

What surprises both of us are the facts about this stellar threesome:

αCentauri-A (large and yellow like our Sun) and αCentauri-B (slightly smaller and cooler) take 80 years to orbit around each other, and they are about 20 times as far from each other as Earth is from the Sun. Wouldn’t it be cool if αCentauri supported a planet like our Earth! αCentauri A and B together form the third brightest star in the sky and the brightest in the constellation Centaurus. With a magnitude of 0.27 αCentauri shines on us from a distance of 4.3 light-years. 

The third star, αCentauri-C, is closest to us and is called Proxima Centauri. What else? It is very far from the central pair; at least 300 times as far as the most distant planet in our solar system is from the Sun! And it’s on a very slow walk round its siblings  – a single circuit takes 500,000 years or more!

Though it is the closest star – 4.2 light years away – we can’t see it with the naked eye, or even our binocs, because it is dim, red and small – about 18,000 times fainter than our Sun.

Summing up the trinity collectively known as αCentauri: 
(i) the two large siblings, each approximately as big as our Sun, waltz around each other every 80 years, at a distance 20 times our Sun/Earth distance;
(ii) the third sibling circles the other two every 500,000 years, at a distance 300 times our Sun/Neptune distance. This is the star closest to our galaxy. 

What does it mean when we say that αCentauri is roughly 4 light years away from us? It means that it takes 4 years for light to travel between αCentauri and us.

αCentaurians, if they were tuned in to Earth right now (Feb 2012), would be just seeing Kevin Rudd, the new Prime Minister of the Labor government make a historic speech of apology to the Stolen generation of Aboriginal people; Barack Obama’s election campaign in full swing; and Castro resigning as President of Cuba! Yes, they would be seeing us as we were in 2008!

This diagram below illustrates a comparison of the sizes and colours of the three stars of the αCentauri system and our Sun.

Relative sizes of Alpha Centauri and our Sun

Relative sizes of Alpha Centauri and our Sun (Click on image to enlarge)

 Position of the Southern Cross during the year

Finding the South Pole, using the Pointers and Southern Cross

Adapted from Wikipaedia http://en.wikipedia.org/wiki/File:Pole01-eng.jpg

Read also a great blog from the Observatory on finding the South Pole: http://www.sydneyobservatory.com.au/2008/finding-south-using-the-southern-cross-an-essential-skill/

Colours of the Cross

Looking closely at the Southern Cross, I notice the different colours. Going clockwise α (Alpha) and β (Beta) Crucis are blue-white, but γ (Gamma) at the top of the Cross is red. δ (Delta) Crucis is blue-white and little ε (Epsilon) Crucis – hard to see without binoculars now because of increased light pollution –  is orange.

Colours of the Southern Cross

Colours of the Southern Cross (Click on image to enlarge)

 There’s more to explore around the Southern Cross, but a Gibbous Moon is competing for my attention right now!

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