Christmas star and the immensity of space

 

 

The vast immensity of space! In our day, I don't think we are nearly as "in touch" with the sky above us as were our ancestors. We don't judge time by the sun. We can't navigate by stars, or discern the seasons. But every now and then, a phenomenon catches our attention and we look up for a while. When that happens, we would be wise to take time to ponder what we see and what it means.

The conjunction of Saturn and Jupiter drew much attention, partly because of the proximity to Christmas and the fact that it happened on the Winter Solstice, the shortest night of the year. As seen by the naked eye, the planets joined to form a very bright star. With a little bit of zoom magnification, you can discern the two separate lights. But it's interesting to understand what really happened. Here are the ponderings of a very amateur astronomer who has been fascinated since he got his astronomy merit badge 50 years ago!

Planets are not light sources; they don't generate and emit light like stars do. They reflect the sun's light. Light travels at over 186,000 miles per second (try to conceive of that!). So for the light to cover the 93,000,000 miles (average) from the sun to Earth takes a little over 8 minutes. To get to Jupiter requires over 43 minutes, and to get to Saturn almost 80.

The distance between earth and the planets varies, because all planets have elliptical orbits in different planes that can bring them closer or farther at various times. Right now, Jupiter is approximately 552 million miles away from the Earth. Saturn is over a billion miles away. A BILLION MILES! How can we conceive of such distances?? (So note that even though the two planets appear next to each other in our sky, they are a massive distance apart; it's just that their irregular orbits happen to line up in our field of vision.)

So for us to see Jupiter and Saturn, we really see only the light that travels from the sun to the planet, and gets reflected back to Earth. The time required for light to make that journey, even at the mind-boggling rate of speed that light travels, requires roughly an hour and a half for Jupiter, and almost 3 hours for Saturn.

Now here's another interesting factor. Jupiter is massive, the largest planet in our solar system. Its diameter is 11.2 times the earth! Saturn is not far behind, at 9.5 Earth diameters. So they have a lot of surface to reflect light. Furthermore, scientists talk about a concept called "albedo" which is basically how much light is reflected vs. absorbed. Earth reflects about 30% of incoming sunlight and absorbs the other 70%. Jupiter reflects up to 50% of the light, and Saturn 34%. So there is quite a bit of the Sun's light being absorbed.

Finally, I think about what it means for light to be emitted from a central point. As light leaves the sphere of the sun and starts to fill the vast emptiness of the solar system, it becomes weaker and more disbursed the further out it gets. Then what portion does manage to arrive at the distant planet and be reflected, has the same phenomenon of disbursal for the return trip. It's amazing that we see anything at all!

The overwhelming impression to me from all of these considerations is to marvel at the astonishing power of light to penetrate the darkness. It really does reach out to "fill the immensity of space" probably in ways beyond our ability to detect and comprehend. As I looked at a pair of planets converging into a "Christmas Star" in the cold night sky, how could I not #GiveThanks for the marvelous wonder of such a magnificent creation!

"And the light which shineth, which giveth you light, is through him who enlighteneth your eyes, which is the same light that quickeneth your understandings;

"Which light proceedeth forth from the presence of God to fill the immensity of space—

"The light which is in all things, which giveth life to all things, which is the law by which all things are governed, even the power of God who sitteth upon his throne, who is in the bosom of eternity, who is in the midst of all things."

D&C 88:11-13