Where’s the Celestial Equator?

Celestial Equator

I started shooting star trails last year and observed that their pattern varies depending on the direction in which the camera is focused. The curiosity to understand the star trails led me to an interesting phenomenon – the Celestial Equator. Hence, during the trek to Singalila Ridge (near Darjeeling, India) in Oct’18, my key objective was to record the Celestial Equator in my pictures.

Firstly, let me answer the most common question asked, “Can we see the star trails?”

Answer is No! Human eye is very powerful but cannot record a scene while a camera can do so on a photo film or digital sensor. As per my settings, a star trail picture is a composite image of minimum 60 frames where each frame has a time exposure of 30 secs. All such frames are shot continuously without disturbing the camera position and settings. Each frame captures the apparent movement of a star due to Earth’s rotation in 30 secs. Individual frames are then stitched together in a photo processing software in ascending order of time sequence to build a single star trail image.

Let’s now take a magnetic compass and explore the night sky….

A) Focus on the North direction as shown by the compass

Earthlings in the Northern Hemisphere are lucky to have a clearly visible star Polaris or North Star about 323 light-years away from Earth. The position of North Star in the sky is aligned with Northern end of Earth’s axis of rotation. It means if the observer is standing at the North Pole, North Star will be seen in the sky vertically above the observer’s head i.e. at the ‘Zenith’.

Now, imagine our observer standing at the North Pole (Latitude = 90 degrees North) starts walking downwards towards the Equator (Latitude = 0 degree). As he moves away from the North Pole, he will see that the North Star is now not visible at Zenith above his head. It actually has shifted down the Zenith towards the horizon.

How much will be the displacement of North Star’s position in sky?

For every 1 degree of latitude walk from North Pole to Equator, North Star will be visually displaced by 1 degree away from the Zenith of the observer’s location and towards the Northern horizon. From the observer’s location, North Star’s position in the sky will be as follows:

  • From the Zenith = Number of Latitude degrees observer is away from the North Pole or From the Zenith = 90 – Latitude of the observer’s location
  • From the Horizon = 90 – number of Latitude degrees observer is away from the North Pole or From the Horizon = Latitude of the observer’s location

When the observer reaches Kalapokhri (my location at Latitude = 27 degrees North of Equator) on India-Nepal border then North Star will appear:

  • From the Zenith = 90 – Latitude of the observer’s location  = 90 – 27 = 63 degrees (angle between Zenith→Observer→North Star)
  • From the horizon = Latitude of the observer’s location = 27 degrees (angle between Horizon→Observer→North Star)

Ok! So, we have identified the angle of view for North Star. Now, let’s check the star trails in the North sky.Fig1

Earth rotates from West to East around its axis which is aligned from North Pole to South Pole. Also, North Star is visible at the Zenith of the North Pole. Thus, due to Earth’s rotation, stars in Northern Hemisphere appear to wheel around the North Star in anti-clockwise motion. This makes the North Star as the centre of circular star trails. North Star appears to be stationary because it is aligned along the rotational axis (North-South) of Earth. It implies that irrespective of the observer’s location on Earth, if the North Star is visible then its position indicates the North direction. This is the reason why North Star is so important for navigation.

At the Equator (Latitude = 0 degree), the angle between Horizon→Observer→North Star = 0 degree. Thus, North Star will not be visible. The star trails will appear like semi-circles centred around the position at the horizon below which lies the North Star.

At the North Pole (Latitude = 90 degrees North), the angle between Horizon→Observer→North Star = 90 degrees. Thus, North Star will be visible overhead at the Zenith. The star trails will appear overhead as circles centred around the North Star and parallel to the horizon. Anywhere in the Southern Hemisphere, North Star will not be visible as it will be below the horizon.

B) Focus on the South direction as shown by the compass

As explained for Northern Hemisphere, all stars in Southern Hemisphere also appear to move around South Pole but in clockwise motion. There is an equivalent to North Star known as Polaris Australis but it is barely visible.

Fig2

In the above picture, you can see that centre of concentric circular star trails is not visible and appears to be at the far-left bottom of the frame. That’s because Sandakphu is in the Northern Hemisphere and South Pole is below the horizon. Now, if we focus towards East or West there should be vertical star trails. Yes, but the magnitude and the angle of vertical trails again will depend on the location of the observer. This brings us to the Celestial Equator!

C) Focus on the West direction as shown by the compass. It should be real geographical West and not the point on West horizon where the Sun sets!

Assume that the observer is standing on the Equator with his arms stretched sideways from left to right and parallel to the ground. If he moves his hand to meet at the top of his head, it results in a semi-circular trajectory. Let’s extend this trajectory up in the sky. This imaginary circular trajectory with an infinite radius in the sky, parallel to the Equator from East horizon to Zenith to West horizon is the Celestial Equator.

The Celestial Equator divides the visible sky anywhere on Earth into Northern and Southern Hemispheres. Thus, at the Equator, one half of the sky towards North of Equator is Northern Hemisphere and the other half of the sky towards South of Equator is Southern Hemisphere. This division of the sky in two equal parts will occur only at the Equator.

What about the other locations on Earth?

To find the answer, let’s ask our observer to face South and walk backwards towards the North Pole. For every 1 degree of latitude walk from Equator to North Pole, the imaginary line dividing the sky called as the Celestial Equator will fall by 1 degree from Zenith towards Southern horizon. This fall is because of the spherical shape of Earth. The portion of the sky North of Celestial Equator will be in Northern Hemisphere and that to the South of Celestial Equator will be in Southern Hemisphere.

Star trails in the Northern Hemisphere will be concentric with the North Star aligned with North Pole and the stars in the Southern Hemisphere will be concentric with the Polaris Australis aligned with South Pole. All stars at or near the Celestial Equator will appear to be moving in almost straight trajectories parallel to the Celestial Equator.

The Celestial Equator will intersect the horizon exactly at the geographical East and West points for the given location. Let’s take the West intersection point and draw an imaginary line from this point to the Zenith. Now, from the observer’s location,

  • the angle between Zenith→Intersection point on Horizon→Celestial Equator = Latitude of the observer’s location or (90 – number of Latitude degrees observer is away from the North Pole)
  • the angle between Horizon→Intersection point on Horizon→Celestial Equator = Number of Latitude degrees observer is away from the North Pole or (90 – Latitude of the observer’s location)

Let’s check the results when the observer reaches Kalapokhri (my location at Latitude = 27 degrees North of Equator) on India-Nepal border.

Fig3

In the Figure 3, it is observed that,

  • angle between Zenith→Intersection point on Horizon→Celestial Equator = 27 degrees
  • angle between Horizon→Intersection point on Horizon→Celestial Equator = 90 – 27 = 63 degrees

Wow! This observation for the intersection angle of Celestial Equator at Kalapokhri is as per the theoretical explanation given above.

When he reaches the North Pole, the Celestial Equator will be located along the horizon (90 – 90 = 0 degree). Thus, the entire sky will be in Northern Hemisphere.

This phenomenon is also applicable when we move towards South Pole from Equator. The Celestial Equator will move towards North by 1 degree from Zenith for every 1 degree latitude walk towards South Pole from Equator.

To summarize, for any location on Earth:

  1. The Celestial Equator divides the visible sky anywhere on Earth into Northern and Southern Hemispheres.
  2. The Celestial Equator will intersect the horizon at geographical West and East points. Its angle of intersection relative to Horizon and Zenith will be same for all observers located at the same latitude anywhere on Earth.
  3. All star trails will be parallel to the Celestial Equator.
  4. All stars in the Northern Hemisphere sky (North of Celestial Equator) will form anti-clockwise star trails with the North Star at North Pole as the centre.
  5. All stars in the Southern Hemisphere sky (South of Celestial Equator) will form clockwise star trails with the Polaris Australis at South Pole as the centre.
  6. At the Equator,
    • star trails in Northern Hemisphere will appear like semi-circles centred around the position at the horizon below which lies the North Star aligned with North Pole.
    • star trails in Southern Hemisphere will appear like semi-circles centred around the position at the horizon below which lies the Polaris Australis aligned with South Pole.
    • star trails in the East and West directions will appear perpendicular to the horizon.
  7. At the North Pole, all star trails will appear parallel to the horizon with centre as North Star visible at Zenith of North Pole.
  8. At the South Pole, all star trails will appear parallel to the horizon with centre as Polaris Australis located at Zenith of South Pole.

Today, we have sophisticated technology to understand various cosmic phenomena. However, modern science is built on the work of our ancestors who identified these concepts by meticulous observations and calculations. I bow to them!

Please visit Image Gallery : With Stars at Singalila

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With Stars at Singalila

Singalila Ridge is located along India-Nepal border near Darjeeling, India. During my trek in Oct’18, I saw different moods of the night sky with Milky Way Galaxy and Stars taking the centre stage…

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Step into the Woods

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Pindari Twinkles

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Julley! Ladakh

Travelogue : 475 Kms To Leh

After a day spent in Manali rains, a cup of hot tea was just perfect to relax and enjoy the view from our hotel terrace. The dark clouds were dominant but the twilight could be seen creating its hue in the sky.

“What time do we start tomorrow for Rohtang Pass?” I asked our group leader Nawang from White Magic Adventure.

“4 am!” Nawang announced. I silently sipped in my hot tea. The idea of starting so early in cold morning made it more desirable.

“But Rohtang is only 40 Kms away and we can reach Jispa in about 5 hours.” I tried to impress him with my knowledge (Thank you, Google!) of the route.

“No, we have to start by 4 am else the traffic will be bad.” Nawang was firm and I wondered if we ever left Mumbai.

Day 1 – June 30, 2017:  We started at 4 am from Manali which now in drizzle, dim street lights and empty roads looked much better! We reached Rohtang Pass entry check post in an hour just when the sun was rising behind the mountains under dark cloud cover. Having started on time, I thought we would be first in the queue but surprisingly there were faster early birds already parked waiting for the gates to open. In a flash, there was a long line of vehicles behind us and we could now see the sense in Nawang’s firm instructions.

Gates opened at about 6am and we were finally on the way to Rohtang Pass. Fortunately, a 10 Kms long tunnel from Manali to Sissu is under construction that will by-pass the Rohtang Pass on Manali to Leh highway. It is expected to be operational by the end of December 2017. When all seemed well, we heard about a landslide that had blocked the highway near Patseo about 170 Kms away from Manali. Our concern was, “What if the highway is shut down for some days?”

We reached Rohtang Pass at 7am and missed the opportunity to experience its beauty due to rains. The visibility was also poor due to thick cloud cover and fog. However, first rule of travel is to enjoy whatever the Nature provides! So, we spent some time here to get a feel of the fresh air at 13000 ft. The cold wind coupled with the splash of rain drops was freezing but it was a good wake-up call. We were now in the nature’s lap…disconnected from the world. Regular assurance from Nawang that the weather and highway ahead will be clear was extra motivation for the group.

5 Kms after descending from Rohtang Pass is a small village – Gramphu (10500 ft) on the banks of the river Chandra. Gramphu is significant because of the diversion of the highway…right turn goes to Spiti Valley and straight forward is Leh! Another 5 Kms brings us to Khoksar (10300 ft) which is the first village in Lahaul Valley region on this highway. Driving through some serene countryside locations of Himachal Pradesh prompted our driver – Tilak to play songs from Himachali folklore. These songs based on local Natti beats provided the ideal background to the pristine views of the clouds playing over mountains and the Chandra river gushing through the plains. When the glaciers melt in the Himalayas, the water flows with full strength and it’s a sight to behold.

A river finds its own path and joins hands with its partners along the way! Chandra that originates from Chandra Tal (a high altitude lake in Spiti Valley) merges with Bhaga river that flows from Suraj Tal in Lahaul Valley. This confluence of the two rivers happens about 25 Kms ahead of Khoksar, in Tandi (8400 ft) resulting in the more popular river Chandrabhaga or Chenab as known in Jammu & Kashmir and Punjab. It is this sangam of Chandra and Bhaga that makes Tandi an important stop-over point in the journey. I could only marvel at the sight of these rivers with different colours silently becoming one and flow together towards their destination.

8 Kms after Tandi is Keylong (10100 ft), the biggest town on this highway. Keylong is crowded and congested giving us a good reason to move on towards Jispa, our last stop for the day. As we approached Jispa, the environment was quiet and peaceful making us wonder if there are any inhabitants in this area. However, that is where Jispa makes its mark as the perfect halt between Manali and Leh. It is located at a height of 11000 ft in a beautiful valley surrounded by hills on the banks of Bhaga river providing good acclimatization for the travellers. 150 Kms between Manali and Jispa was covered in about 7 hours giving the group a good rest time for the day.

Any thought of being connected with the virtual world was grounded with a message on the hotel’s reception board… “No Wi-Fi! Imagine it’s 1947 and enjoy nature!” … when the charm of nature takes over, it is possible to live (ok! at least for some days) without being dependent on the marvels of the technology that dominate us in our daily city life. We were soon informed that highway to Leh is fully operational thanks to brilliant repair work by Border Road Organisation (BRO) of Indian Army. Our excitement was soaring high…

Day 2 – July 1, 2017:  We left Jispa in drizzling rain at 5 am for the best part of the journey…Jispa to Leh, a distance of 325 Kms through some of the highest mountain passes in the world. I had read some stories about this amazing highway inspiring me to take this journey. Now, I was curious to know…what will be my story?

The visibility was poor due to the fog when we passed through Deepak Tal (12500 ft). By 6 am, we were at Patseo where the landslide spot had been cleared by BRO. 10 Kms ahead is Zingzing Bar (14000 ft)…no buddy! It’s not a pub! Zingzing Bar is a small area with some tented options for a quick round of tea and snacks before ascent to Baralacha La Pass (16100 ft). It also marks the beginning of the drive through high altitude route beyond 14000 ft till Upshi in Ladakh. The fog was so thick that nobody realized that we were passing through Suraj Tal (16100 ft) till Nawang enlightened us. Suraj Tal, source of Bhaga river, is the second highest lake in India but we missed a clear view of its beauty. Hmm…it was disappointing but surely better luck is just ahead!

After a brief halt at Baralacha La Pass to savour some memorable moments amidst light snowfall, we reached Killing Sarai (15100 ft) at 7:30 am for a cup of hot tea and Maggi noodles, which I feel for some reason tastes better in the mountains. We met a group of 4 young bikers who were also travelling towards Leh and had taken a night halt in the tented accommodation. They had to break their journey due to bad weather previous day and were delayed by about a day in reaching Leh.

“So, any plans to make up for the lost time?” I asked to learn more about a biker’s mindset.

“No, we are used to it. In the mountains, safe ride is more important than time.” He answered with a smile.

“Good! All the best!” I was happy to see their maturity and wondered if they will have the same answer back home when driving through the city.

Their enthusiasm and spirit for travel was admirable. Often strangers meet for a short time but are remembered because of an unspoken travellers’ bond that encourages each other to achieve the goal. When good words are shared, nature also turns friendly! The weather began to change. Bright sunshine through the clouds over a blue sky cheered up Bhaga too and it was now glowing with a silver touch. The landscape so far had a touch of vegetation but now it was fading away to reveal a terrain that was barren in different shades of brown that is trademark of Lahaul-Spiti-Ladakh region. Due to lack of vegetation, oxygen level in the atmosphere also starts reducing which should not be ignored and proper precaution is advisable.

At 9 am, we reached Sarchu (14100 ft), about 225 Kms away from Manali almost at the midpoint of Manali to Leh highway. It also has two key transition points to its credit. First – Manali to Sarchu part of the highway is managed by Project Deepak – BRO and from Sarchu to Leh it is managed by Project Himank – BRO. Second – Sarchu also marks the end of Himachal Pradesh and start of Jammu & Kashmir. Sarchu has some tented accommodation. During tour planning we had thought of taking a break here on the way to Leh. However, this is an extremely windy location and not advisable to stay on the Manali to Leh route. Sarchu’s altitude is higher than Jispa and Leh. As a result, high altitude acclimatization is not yet adequate for overnight stay in Sarchu. Travellers prefer to halt here when travelling from Leh to Manali because they would have already been acclimatized passing through some high altitude passes before reaching Sarchu from Leh.

25 Kms beyond Sarchu starts an interesting road construction by BRO. There is a series of 21 turns called as Gata Loops (13800 ft) which lifted us in about 30 minutes to Nakee La pass (15500 ft). There are some viewpoints mid-way on the Gata Loops from where one can see the road bends overlooking the deep valley below. Passing through Nakee La, Nawang pointed at a narrow path cutting through the mountains. In olden days, Ladakh’s Royal family members were carried in palanquins on that path to travel across the region. One can only imagine the plight of the poor servants who did this job.

The next milestone was Lachung La Pass (16616 ft) which is the second highest mountain pass on this highway. We were now travelling through some of the highest passes in the world accessible by road. Descending 30 Kms from Lachung La Pass, at 1 pm we took a lunch halt at Pang (15100 ft). 7 hours road trip through high altitude region was tiring but Leh was still 175 Kms away and it is better to reach there before sun sets for the day. Hence, we quickly moved on from Pang.

The weather was at its best…cold with bright sunlight. The patterns formed by thick white clouds over a crystal clear blue sky were our companion.  The sun and clouds engaged in a play that formed shadows over the canvas of barren mountains which are not made of hard rock that can stand the test of time. As a result, soil erosion causes these hills to gradually break into fine grain and be dusted to ground. The fragile texture of the geography makes it difficult for construction of roads, tunnels and railways in this region. Nevertheless, due to the erosion nature sculpts interesting carvings and slopes on the mountain surface.

While admiring the nature’s artistic work, we suddenly came to what looked like a runway at airport! It is the Moore Plains (15520 ft) – a 50 Kms road built on a plateau. Maybe it was a buffer to relax before ascending to the highest point on this highway – Taglang La Pass at an imposing altitude of 17500 ft. The view from this height was breath taking. Mountain ranges that looked huge from lower heights were now at the base of this mighty pass. Himalayan ranges with snow-capped peaks could be seen far into the horizon. Who would want to leave such a place? However, we had to move on because the wind blowing cold and strong at such a great height brought everything except Oxygen! The weather conditions here need to be respected and to avoid any adverse affect one must not stay for a long time at Taglang La Pass. Interestingly, we came across a nomadic tribe that was on their way to a new destination. They were shy and reluctant to speak. I couldn’t believe that any human can actually live in this area where I was finding it difficult to hold my ground.

At 3:30 pm, we descended to Rumste (14000 ft) which is the entry point into Ladakh. There is some vegetation here with Indus River flowing by the roadway as a welcome gesture. 30 Kms further is Upshi village (11400 ft) where after almost 12 hours of travelling we could see some signs of human settlement with farm fields, houses and petrol pump station…villagers busy with their daily chores and children waving with a broad smile! After a magical experience of the high passes, this too was heart warming. Another 50 Kms and we finally reached our destination – Leh (11500 ft) at 6:00 pm…13 hours…325 Kms after leaving Jispa. Starting from Manali we had travelled ‘475 Kms to Leh’.

The group was numb and tired. The excitement and happiness could be sensed but no one had the energy to express it. A smile delivered the message. I remember asking myself, “What have I just done? Wasn’t this the most adventurous road trip of my life?” It took me sometime to return from the illusion gone by…that was perhaps a different world with no one except for the Creator busy with His craft…and I was privileged to be there.  In two days, I experienced all the seasons – charming rains, teasing snow flurry, bone chilling cold, comforting sun…a panorama of nature’s beautiful canvas – rough terrain, gentle flatlands, gorgeous colours, five high mountain passes, natural carvings, rivers flowing alongside…every element in harmony…Ah! serene art of the Divine. My journey became more significant than the destination…

Please click here for Image Gallery : Julley! Ladakh

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Somewhere…in India!

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Wherever the Mountains take me…