Greetings, stargazers.
Beside the moon, the three brightest objects in the sky are all visible right now. Venus in the west, Jupiter in the east and Sirius, the only one that is an actual star, is high in the south.
In some parts of the country, you can distinguish planets from stars because the planets don’t twinkle like the stars. However, with some of the turbulent atmospheric conditions caused by large day/night temperature swings in the Four Corners, I have seen even the planets twinkle at various times.
I was recently asked why Jupiter wasn’t much brighter than Venus. Since its radius is about 10 times that of Venus, it has about 100 times the surface area to reflect light toward Earth.
Yes, Jupiter is much farther away than Venus, but a linear effect wouldn’t completely explain the brightness differences. To do that, you need the “one over distance squared” effect. This is well-known to scientists, but is typically not thought about by casual observers.
When light spreads out from the sun, or from any light bulb, the farther away from the source the light gets, the larger the area that has to share the same light. That area increases as the square of the distance.
Think of lighting up a room in your house that is 10 feet on a side with a single light bulb. If you try to get the same level of lighting in a room that is 20 feet on a side, you would need four light bulbs. Or, that single light bulb from the 10-foot room would illuminate the bigger room only one-fourth as much.
Since Jupiter is about five times farther from the sun than the Earth, the sunlight it receives is only about 1/25th as intense as that shining on Earth. The reflected light leaving Jupiter also spreads out the same way as it heads back toward us.
This month
Tonight, a very dim (and much farther away) Mars will be within half a degree of the very bright Venus. Look for the evening star’s faint companion shortly after sunset.
The Dawn spacecraft is scheduled to arrive at the dwarf planet Ceres on March 6. Launched in 2007, Dawn visited the asteroid Vesta in 2011. Ceres was the first asteroid discovered (1801) and has since been re-classified as a dwarf planet.
Recent photos from Dawn have been quite a treat, and as the spacecraft gets closer, they will be even better. Although Ceres should be a relatively easy binocular target, right now, it is toward Sagittarius, a summer constellation.
hakes_c@fortlewis.edu. Charles Hakes is an assistant professor in the physics and engineering department at Fort Lewis College and is director of the Fort Lewis Observatory.
Useful links
News about Dawn and other NASA missions: www.jpl.nasa.gov/news
Astronomy picture of the day: http://apod.nasa.gov/apod
An astronomers forecast for Durango: www.cleardarksky.com/c/DrngoCOkey.html?1
Old Fort Lewis Observatory: www.fortlewis.edu/observatory
Four Corners Stargazers: http://groups.google.com/group/Four-Corners-Stargazers
