Published: May 03, 2008 06:27 pm         

How well do you know our planet?

Do you know your planet?

Our new public planetarium for May at Frostburg State Planetarium is “Report on Planet Earth,” starting today at 4 p.m. and 7 p.m.. Lately, there have been a number of documentaries on the future of our Earth’s environment, especially in regard to our consumption of energy and resources.

“Report on Planet Earth” deals with the basic information about our planet, in a way that one can better evaluate these other presentations.

Prior to this main feature, we have an informal tour of the evening and morning skies using our Planetarium Projector, with our stars looking better than ever. This sky introduction (SkyWatch) covers sky basics, the best sights to see both this spring and during the coming summer months and the most frequently asked questions about the sky (such as, Why Isn’t Pluto a Planet?). SkyWatch is at a level for the entire family; a free summary with a May sky map is available to visitors.

“Report on Planet Earth” has three parts: Key Earth Numbers, Earth Myths and Main Earth Processes (that give our Earth conditions suitable for life). All through both SkyWatch and ”Report,” live questions and comments from the audience are welcomed and encouraged, making our presentations quite different from those on television or on DVD. Both SkyWatch and “Report” together last less than an hour.

Following a brief intermission, our planetarium visitors and others are invited to tour the Compton Center Exploratorium at 5 p.m. and 8 p.m. where a fabulous collection of animals from five continents and Oceania are on display. All these presentations are free to the general public from the Tri-State area.

There are no reservations or tickets needed, but please note times above; latecomers can’t be admitted to the Planetarium once our audience’s eyes become dark-adapted. Call (301)687-7799 to request a free bookmark with small campus map included sent to you.

The five key Earth numbers are: Earth’s circumference of about 25,000 miles, Earth’s solar distance of 93 million miles, Earth’s average global temperature of 58 F, Earth’s surface acceleration of gravity of 32 feet per seconds squared and Earth’s surface air pressure of 15 pounds per square inch. Each number determines in a fundamental way our Earth’s surface conditions. A few of these numbers have interesting stories behind them, some involve laborious measurements and yet others are those we experience each day.

Twenty-four centuries ago the ancient Greeks knew that the Earth is round. In the 3rd century BCE, the Greek scholar Eratosthenes of Alexandria determined the distance around the Earth to a few per cent; this was 18 centuries before Magellan’s expedition actually traveled around the world. Eratosthenes calculated the Earth’s circumference by noting the difference in day shadows between his city of Alexandria and the city of Syene, 500 miles to the south.

The sun’s distance of 93 million miles was first estimated by passages of the planet Venus in front of the sun in the 18th century. Our current accurate value comes from observations of the planet Venus and radar measurements of Venus’ distance when closest (then nearly in line with the sun).

Our average global temperature of 58 F is based on compilation of temperatures measured at sea, in the polar regions, deserts, farm fields, etc. National Weather Observers (such as Dr. Greg Latta) make measurements of air temperature each day away from concrete, buildings etc. to get accurate temperatures that go into the average global average temperature figure.

The surface acceleration of gravity tells the increase in speed per second of a free falling body. The first measurements of gravitational acceleration were made by Galileo more than four centuries ago. In metric units, we multiply a body’s mass (in kilograms) by the acceleration (in meters per second squared) to find the body’s weight in metric units (Newtons).

On the moon’s surface, the acceleration of gravity is only 1/6th that on Earth’s surface. This allowed the Apollo astronauts to wear 200-pound spacesuits (on Earth) comfortably as they explored the moon’s surface.

Our surface air pressure as measured by barometer is an important indicator of fair weather and approaching stormy weather. Here we note the change in air pressure rather than the air pressure itself (which drops with increasing altitude). Air pressure is how straws work (to push fluids upwards), using air pressure as we create a lower pressure in our mouths.

Moon’s return

On Tuesday at dusk, you may see a very slender crescent moon low in the west northwest. Just above the moon and to the right is the planet Mercury. The best time to see both objects will be about 9:45 p.m. On Friday evening, the crescent moon will appear below the planet Mars and the dim Beehive star cluster. Look above the moon to see the star cluster close to Mars. Mars has a yellowish tint and shines steadily in contrast to the twinkling stars. On Saturday night, the moon will have moved above the planet Mars.

This Saturday is National Astronomy Day. The Cumberland Astronomy Club will have a number of big amateur telescopes outside of Tawes Hall Planetarium for public viewing of the moon, the planet Saturn and star sights that evening. At 8 p.m., there will be a showing of “Report on Planet Earth” in the Planetarium. As this program finishes, the sky will be dark enough for planet and star viewing through the telescopes. All interested are invited.

There’s plenty of convenient parking near Frampton Hall. As well as close by handicapped parking, there is a ramp leading to Tawes Hall for the less mobile.

Bob Doyle invites comments and questions from readers; his email is rdoyle@frostburg.edu .