Sunday, February 28, 2010
The lion enters then the lamb exits
John Goss
John Goss is chairman of the Mid-East Region of the Astronomical League and a former president of the Roanoke Valley Astronomical Society.
Recent columns
- When were the stars born?
- Moon, Venus, Jupiter in a predictable dance
- Look far beyond the stars of the Milky Way
- The planets lead nomadic existences
Blog
We often hear at this time of year, "March comes in like a lion and goes out like a lamb." With the winter that we've been having, many of us would rather that March came in like a lamb and stayed that way! Nevertheless, in an astronomical sense, every year March must come in like a lion and must go out like a lamb. What is this all about?
As March begins, the prominent constellation Leo the lion rises in the east as evening darkness settles. In some years, such as this one, the weather roars like a lion. But, in every year, the lion enters the eastern sky. So, March comes in like a lion.
As March begins, a less conspicuous constellation, Aries the ram, sits high in the west. By month's end, though, Aries sets in the west shortly after sunset. Regardless of weather conditions, every March ends with the ram -- err, lamb -- leaving the western sky. So, March goes out like a lamb.
If our sun was 1 million times dimmer, it would be easily seen as a dull yellow ball cast against the background stars. As our Earth orbits that eerie orb, those stars would continuously shift westward on the celestial dome while the sun would appear to move past them in an eastward direction.
Over the first few days of March, the sun is positioned far to the west of Aries. So far west that the sun sinks considerably below the horizon before the stars of that constellation emerge in the darkening sky. Since the sun moves farther eastward every day, it slowly approaches Aries. As a result, the ram lies much lower in the west just after sunset at the end of the month. The sun finally catches the stars of Aries four weeks later when they all set together. (The same description of events can be said of Leo, although it takes the sun until late August to reach the stars in that part of the sky.)
Aries is not an easily recognizable pattern of stars and requires a relatively dark sky to spot. Its brightest luminary, Hamal, 66 light-years away, is about as bright as the major stars of the Big Dipper. On the evening of March 18, the softly glowing crescent moon hovers to its lower left, allowing a positive identification of Hamal. One night later, the moon moves to the left of the constellation's easternmost member, the unassuming 41 Arietis.
Twenty-four hours later, the moon lies one of its own diameters below the Pleiades star cluster, also called the Seven Sisters. Use binoculars to count the faint "Sisters" as they drop toward the western ridgelines. They may not be clearly visible because of the moon's glare and, even though its nickname suggests otherwise, there may be many more than seven glittering lights.
On the same night (March 20), look directly east for a bright starlike object rising below Leo. This is the second largest planet in our solar system, the 800-million-mile-distant Saturn. Draw an imaginary straight line beginning at Saturn, passing through you, and cutting through the Earth below the western horizon.
After 93 million miles more, that line intersects the sun.
The sun happens to be positioned on the celestial equator, which is a projection of the plane of the Earth's equator onto the sky. This means that the sun is crossing the vernal equinox and marks the arrival of spring.
For many people, that's not a day too soon! Will that day be more like a lion or more like a lamb?
For more astronomy news, see the Curious Skywatcher blog at roanoke.com/blogs.
