By Prasad Ganti
Last winter, I was driving across Pennsylvania in the middle of the night from the western border with Ohio to the south eastern border with New Jersey. I saw Orion the hunter, the most prominent constellation in the winter skies. It rose from the east and rose higher and higher in the sky. As I turned south, I saw the Canis Major constellation with the brightest star Sirius. The dark skies in the rural areas providing a good astronomical feast for the eyes. With straight highways and almost no traffic, frequently stealing glances at the sky was a pleasant memory.
A thought then stuck me. How do the stars and star formations look from different vantage points. The vantage points could be on the Earth. They could be on another planet in our solar system. Or some point in our Galaxy or some other point in the Universe. I am sure the sky would look different. But just how different? Let us start with our home, the Earth. I did not observe the sky significantly from any country other than the US. I remember seeing the winter sky in India a few years back. But the light pollution in populated cities is a major deterrent. The Orion looked similar from India. It is so significant in size that I am assuming it looks very similar from whole of the northern hemisphere.
The skies look differently from the southern hemisphere. In countries like Australia, New Zealand, Chile, Argentina etc. In the northern hemisphere, the pole star or the north star (called the Dhruv in India) stays at the same position in the sky night after night. It is visible at different points from the northern hemisphere but not at all from the southern hemisphere. It is higher up in the sky when approaching the north pole. It is lower in the sky as we approach the equator. In the southern hemisphere, the equivalent of the north star is the southern cross. This is not visible from the northern hemisphere at all. Our nearest star (other than our own Sun) is the Alpha Centauri, which is about four light years away. This is visible only from the southern hemisphere. Similarly, the hazy cloud called the Large Magellanic Cloud is also visible from the southern hemisphere only.
If we go to Mars, how will it look ? Probably similar to what is on Earth. The north and south hemisphere and the seasons (because the axis of Mars is also titled like the Earth) offer different views. But from the interplanetary space, the glare of the sunshine may block all the views of the stars, unless we pass into a planet’s shadow. Far from the Sun, like Pluto or the Kuiper belt, the Sun itself looks very faint, almost like a star rather than as Sun, the view may be more uninhibited with the whole dark sky at the same time.
In the interstellar space, the view will certainly be different, depending on where in the Universe we are located. The constellations will not be visible. Each point will have its own constellations. That is different shapes which can be interpreted as confirming to a pattern. Then there are two phenomena which will produce totally different views. First is the visual binaries. The two stars which appear very close to each other, because they are on the same line of sight from the Earth. Actually they may be very far from each other, but being on the same straight line, appear to be very close to each other. The line of sight will be different from any other place in the Universe. But from that vantage point, there could be other pairs of stars which appear as visual binaries. Those set of stars may not be visual binaries as seen from the Earth.
Second phenomena is the Gravitational lensing. If a star is hidden by a massive object (like a galaxy) in the line of sight from the Earth, the hidden star will appear as a ring around the massive object. Produced due to bending of star light by the massive object.This ring is called the Einstein’s ring. Since this phenomena has something to do the line of sight, it will not look like an Einstein’s ring from a different point in the Universe. Likewise, that point may have its own Einstein’s rings.
I am sure there is a place in the Universe where both Milky Way and the Andromeda galaxies will look as small and hazy lumps. Where would it be ? Can we dream of reaching there ?