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How can astronomers know things for certain since they only look at space from one vantage point?
Category: Space
Published: June 3, 2014
By: Christopher S. Baird, author of The Top 50 Science Questions with Surprising Answers and physics professor at West Texas A&M University
Astronomers do not look at space objects from only one vantage point. You may think that since we are stuck on earth looking out towards space, we can only see space objects from a single viewing angle, and therefore our knowledge is limited. For instance, you may think that perhaps there is an alien city on the far side of the moon, but we don't know for sure because we can't see the far side of the moon from earth. Actually, there are several ways in which astronomers do indeed observe space objects from multiple vantage points.
1. Space Probes and Manned Space Voyages.
In reality, humans are no longer confined to the earth. Over 500 humans have voyaged into space and a dozen of humans have even walked around on the moon. Furthermore, hundreds of space probes have ventured all over the solar system. All of these astronauts and space probes have allowed us to observe the sun, the moon, and the planets in our solar system from many different vantage points. Although the far side of the moon is constantly hidden from earth's view, we know there is no alien city there because numerous space probes and astronauts have seen the far side of the moon. (You can look at the far side yourself, if you are curious.) Many space probes are specifically sent to continually orbit space objects such as the moon or Mars, and therefore are able to look at these objects from effectively all angles.
2. The Rotation of Space Objects.
Most stars, planets, and moons spin around their own axis. This means that every moment in time, telescopes are looking at a specific space object at an angle that is different from that of previous moments. For instance, the sun rotates once about its own axis about every 30 days (the sun's equator spins faster than its polar regions, but that does not concern us here). If you take pictures of the sun continuously for 30 days as it rotates, then you have a photo collection of what the sun looks like from all vantage points. SOHO does just that. Note that the sun is a turbulent ball of bubbling plasma, so its surface features are slowly evolving. But thanks to its rotation, we are able to see what a particular sunspot looks like from the top, from the side, and from all sorts of other angles.
3. Repeated Objects with Different Orientations.
The observable universe is very big and is filled with very many objects. As a result, we can find many objects that are nearly identical to each other scattered throughout the universe. These objects are typically oriented differently in space, so that from earth we are able to effectively view the same object from many different angles. For instance, there are billions of spiral galaxies in the observable universe, all oriented differently in space. By looking at many of these different spiral galaxies, we are able to effectively look at one spiral galaxy from many different vantage points (insofar as general features are concerned). We have found that spiral galaxies have a central, round bulge, and an outer disc of spiralling arms. Much of the certainty in astronomy comes from looking at many different objects that are all of the same class and amassing data from all of them into a coherent whole.
4. Repeated Observations using Different Methods.
There are more ways to "look" at an object than with our eyes or with a camera that captures what our eyes see. Even if we observe a space object from only a single viewing angle, we can effectively see it from different vantage points using different observation methods. For instance, we can look at a star using a camera that captures radio waves, microwaves, infrared waves, ultraviolet rays, x-rays, or gamma rays. We can measure the star's composition using spectral analysis. We can measure a star's relative velocity using redshift observations. In this way, certainty about a star's nature can be established by observing it using many different methods, and checking to make sure all these observations agree.