How to tell the stars are moving

For thousands of years we have used the stars as a symbol of stability. Objects that are fixed in the firmament giving us a sense of steadiness knowing that they would always be there right where we expected to see them in the night sky.

We could depend on them to tell us when the seasons changed, when to plant, when to harvest, and when the hunting would be the best. We knew they would be there when and where we expected them to be.

The only objects that were known to move were the moon and the planets (and the Sun before it was discovered that it was the only thing truly fixed in the sky and then it was discovered that it moved too).

Star movement against the stellar background was discovered by Edmund Halley in 1718 (yes, that Edmund Halley) when he compared the current location of stars against their recorded position in the Hipparchus catalog of almost 2,000 years ago.

This motion is called "proper motion" and is defined as the "apparent observable change in position of a star on the celestial sphere." Another way to determine stellar motion today is to compare photographs of stars from several years ago to photographs of those same stars today.

When the photographs are compared -- it is called a "blink test" -- it will be obvious that there are stars that have moved. That is also how the planet Pluto was discovered.

Now, I don't want to get too technical here, but there is some technology involved. One reason stars don't appear to move is their great distances. Some are hundreds or thousands of light years from us and any detectible movement would not be noticed in one's lifetime.

There are three ways a star can be observed as moving; 1. Across our line of sight, 2. Towards us, or 3.Away from us. The closer a star is, the faster it seems to move relative to our position around the Sun and distance to the star in question.

The star with the fastest proper motion is Bernard's Star (named for astronomer E.E. Bernard) a faint red dwarf star located in the constellation Ophiuchus (pronounced O-fee-ooh-kus) located about six light-years away and after the triple-star Alpha Centauri, the fourth closest star to the Sun.

It moves across our line of sight at about 10.25 arc seconds per year (3600 arc seconds equal one degree). At that speed it will travel about .25 degree in the average human lifetime. Just for comparison, the moon is .5-degree wide. Sorry, it is too dim to be seen without a large telescope.

It is also moving toward us. It will make its closest approach to the Sun around 11,800 AD, when it approaches to within about 3.75 light-years. Just in case you wanted to mark your calendar (but you still will not be able to see it).

SKY WATCH: Full moon yesterday, June 2, which will pretty much wipe out any early evening viewing for the next few days.

However, our Venus watch won't be bothered. Venus, located above the western horizon will be distinctly in view, as will its soon-to-be-companion, the giant planet Jupiter. Keep watching the two as the days pass for their close conjunction on June 30. Venus will be at its greatest eastern elongation (as far east of the Sun as it is going to get) on Saturday, June 6. That means it will be above the horizon for about three hours after local sunset and not set below the horizon until after midnight. Good time for some telescopic viewing of both planets. Also a great time for using a telescope on the planet Saturn. At about 10:30 pm, local time, it will be above the southeastern horizon and the moon won't be up until after midnight.

NEXT WEEK: Summer is a comin' and why astronomers are not happy about it and more astronomical blathering.