With binoculars, you may be able to spot Mercury just above the eastern horizon shortly before sunrise during the first half of April. This little planet is hard to study from Earth since it is always so close to the sun.
Venus beams as the ''Evening Star'' this month. Look for it high in the western evening twilight. On April 2 and 3, it shines in the midst of the beautiful Pleiades star cluster. A thin crescent moon will be near Venus on the evening of April 24.
Reddish Mars is still fairly bright, although it will grow dimmer every week as Earth, in its faster orbit, pulls farther away. The Red Planet is high in the southern evening sky, to the left of the fast-spinning star Regulus.
Article Photos
Jupiter shines brightly in the western sky soon after sunset. It sinks lower each day and will disappear into the solar glare at the end of the month as it prepares to swing behind the sun. A thin crescent moon appears just above Jupiter on the evening of April 22.
Saturn rises in the east-southeast after dark. It is above and to the left of the blue-white star Spica. A small telescope will enable you to see the beautiful rings that encircle Saturn.
The Lyrid Meteor Shower peaks on the night of April 21-22. These fast meteors vaporize after hitting our upper atmosphere at nearly 108,000 miles per hour.
TAKE A DEEP BREATH
''It is better to have your head in the clouds, and know where you are ... than to breathe the clearer atmosphere below them, and think that you are in paradise.'' - Henry David Thoreau
Earth has a very unique atmosphere, unlike that of any other planet in our solar system. Its composition has evolved over billions of years and is still changing. At present it contains 78 percent nitrogen, 20 percent oxygen, 0.9 percent argon, 0.031 percent carbon dioxide, and trace amounts of several other gasses. The amount of water vapor near sea level can vary from nearly zero to about 4 percent (at 100 percent humidity) and averages about 0.8 percent. Above 5 miles in altitude, there is almost no water vapor.
The concentration of carbon dioxide has greatly increased during the past two centuries, due to living organisms, volcanic eruptions and the burning of fossil fuels. Today, we are facing serious atmospheric problems, such as global warming, as a result of the greenhouse effect, damage to the ozone layer and increased acid rain.
There are five distinct layers in Earth's atmosphere, based on differences in temperature, density, movement of air cells, and chemical composition:
The Troposphere extends from the Earth's surface up to an altitude of 4-12 miles. The height varies from just under 4 miles at the poles to approximately 12 miles at the equator. Nearly all of the weather that we experience occurs in this thin lower layer and approximately 90 percent of all the molecules in the atmosphere are found at this level. In this region, cells or packets of air rise and fall with changes in temperatures. As you climb higher, the air becomes thinner and the temperature drops to about minus 60 degrees F near the top of the layer. Many people who normally live close to sea level have temporary problems breathing when traveling to high mountainous terrains. The highest permanent human villages are located at an altitude of 3 miles and these sites are usually cold and windy.
The Stratosphere is found at an altitude of 12-31 miles from our planet's surface. In this layer, the temperature increases with height and reaches about 5 degrees F at the top. Air flow is mostly horizontal in the stratosphere and commercial jet aircraft fly in the lower levels of this layer to avoid the turbulence that occurs in the troposphere below. At times, jet aircraft deviate quite far from their usual flight path in order to gain a boost in air speed from the jet stream in the lower levels of the stratosphere.
About 90 percent of the ozone present in our atmosphere is found in the stratosphere. The oxygen we breathe is made up of two oxygen atoms but ozone contains three oxygen atoms. The ozone found at ground level is a dangerous pollutant but the ''good'' ozone in the upper levels of the stratosphere is vital to our survival, protecting life on Earth from the harmful solar ultraviolet rays.
The Mesosphere is located at an altitude of 31-56 miles from Earth's surface. In this layer, the density of the gasses and the temperature decrease with height. At the top of this layer, temperatures are about minus 184 degrees F. It is in this layer that many of the meteors vaporize as they hurtle inward from outer space, leaving bright trails in the night sky.
The Thermosphere extends up to 375 miles above the Earth. The gasses in this layer are extremely thin (the gas atoms are very widely spaced) but the molecules that are found here help to absorb the deadly incoming high energy X-ray and ultraviolet radiation from the sun. The International Space Station orbits within this layer. This is also the layer in which auroras occur when charged particles from the solar wind spiral along the Earth's magnetic field lines.
The outermost layer of our atmosphere is called the Exosphere. Many satellites orbit the Earth in this layer, which extends out to about 6,200 miles above our planet's surface. At this altitude, the pressure is nearly that of a vacuum and atoms and molecules are capable of escaping into outer space. There is no exact altitude where the atmosphere ends. It just continues to get thinner and thinner until it merges with outer space.
About every 11 years, the solar sunspot cycle reaches maximum and solar activity increases. As a result, the extreme ultraviolet radiation heats and expands our planet's atmosphere, causing it to extend farther into space than usual. This creates increased aerodynamic drag on satellites in low Earth orbit, resulting in orbit decay. Some of the newer satellites have onboard jets that enable the crafts to reboot themselves back up to their original orbits.
Editor's note: This monthly guide to the stars is from the Marshall Martz Memorial Astronomical Association, the Southern Tier Astronomy Recreation Society, and The Post-Journal. For further information, contact the M.M.M.A.A. at www.martzobservatory.org or S.T.A.R.S. at www.UpStateAstro.org/stars/stars.html.