Keeping our stars, and planets, in a row

I enjoy receiving questions from readers. One, it lets me know there are people who are actually reading this column; and two, there are people who have had their curiosity piqued. Such is the case this week.

This particular reader asks, "I have noticed that the moon repeatedly passes near several stars and the planets, why is this?"

Good question. It is what I call the "Celestial Superhighway." In astronomical terms it is called the ecliptic. The ecliptic is the path the Sun seems to follow across the sky.

We all know the Sun does not move -- well, yes it does, but not in the way we are discussing this time. The apparent change of background stars is the result of Earth orbiting the Sun. As we observe the constellations rising each evening they seem to rise, on average, three to four minutes earlier.

This change is due to Earth's orbital movement.

The ecliptic is also the path the moon and planets follow in their orbit, so, each month as the moon--whose orbit is inclined about seven degrees--will be close to the stars and planets that are close to the ecliptic.

The ecliptic is also the plane or our solar system, which is why the planets follow it too, for the most part.

Imagine if you will a Merry-Go-Round (MGR). For the sake of simplicity, let us use the ordinary playground variety.

Now, put a large yellow ball at the center and take a seat on the edge. As the MGR turns, from your seat on the edge the background will appear to change with each rotation. After so many times around you will begin to recognize that you are seeing some of the same things over and over.

Such is it with the planets and stars laying along the ecliptic. Now, let's throw in the moon. It too follows the ecliptic and visits the same objects at least once a month. The background stars will ultimately change as Earth progresses in its orbit.

Thus we see the stars change with the seasons, which we are observing right now. Have you noticed that the Summer Triangle is now directly overhead, and the eastern horizon now has new constellations to look at.

Pegasus, for example. Pegasus is just now rising in the east and is one of the prime constellations of autumn, so without consulting a calendar we can know that a seasonal change is coming.

Now, I have said all that to say this. Next week, starting on Aug. 27, I want you all to go out about 8 pm MDT. This should be about a half-hour after sunset. The sky may still be a bit bright, but you should be able to find a slender two-day old moon just above the western horizon.

Here is your homework, each night go out at about the same time and observe where the moon is, record what it is near, and follow its location each day. Now, about Wednesday, Sept. 10, you will need to change your observing time to after midnight.

Also record your estimation of the stage of the moon. Keep your records, because next month you are going to do it again. After a while you should be able to have a good idea where the ecliptic is.

SKYWATCH: New moon, Aug. 25. Jupiter and Venus are still close in the morning sky, and will still be in the same field of binocular view, so will the Beehive Cluster, M-44. In the west just after sunset Mars and Saturn are still very close, also can be viewed in same field of view. The moon joins them on Aug. 31.

NEXT WEEK: More astronomical blathering.