• Tom Butler

Night Sky

I have just snapped a few pictures of the night sky tonight (November 18) to share with you. The one that I have included here shows our Moon, above it and slightly to the left, the planet Jupiter and above that and to the left, the planet Saturn. To the right of the moon are some faint stars of the constellation Sagittarius.

This is just the beginning of "the show." Every 19.6 Earth years, Jupiter "passes" the planet Saturn. Jupiter's orbit of our Sun takes 11.86 years. Saturn's orbit of our Sun takes 29.4 Earth years. So the next time you will see these two planets close together will be October 31, 2040! Following that it will be April 7, 2060. This kind of event is called a conjunction, meaning a coming together. In reality, Saturn is way beyond Jupiter. They aren't close at all. They just look like they are close when observed from Earth.

Tonight the moon's position is below Jupiter, where will it be tomorrow night? Moon moves very quickly across the sky. Jupiter moves much more slowly. It is approaching Saturn as Saturn is even more slowly moving away from Jupiter. Their closest approach will occur on December 21, 2020. The two largest planets in our solar system will appear just a fraction, 1/10 of one degree apart.

So this is a show to be watched over the next month. Catch the show every clear night.

An example of the effect of size and distance on brightness, the three objects differ greatly in brightness. The photo shows an overexposed Moon, a bright Jupiter and a dimmer Saturn. Our Moon is the smallest of the three objects but is very close. Jupiter is by far the largest of the three and Saturn is about 1/4 smaller than Jupiter but Saturn is the most distant object of the three objects.

If you look higher overhead, you can see another bright planet, Mars. It is nearly due South in the early evening. We have just passed Mars about a month ago at a point where our orbit comes closer to Mars. This makes Mars much brighter now than it will be the next time we pass it in orbit. All planets have elliptical orbits. At times they are closer to each other than other points in their orbit. When Earth is at a most distant point from our Sun (in summer) and Mars is at a close point to our Sun it it's orbit, our two planets will be closer and Mars will appear brighter. We are now past that point but Mars remains brighter than normal. When will our Moon pass Mars?

A little different different look at our Moon, Jupiter and Saturn a day later (November 19). This exposure shows the horizon, the homes within our park. The streak on the right is a helicopter headed north out of McAllen Miller International Airport. Note how far our Moon has moved in relation to the planets. Closer objects move faster!