by Jim Maynard
Star date: 05:21:97
Finding Venus this week requires a patient, diligent search, and low horizons to your west / north west. Look for it low in this part of the sky right after sunset. The lower your horizon, the later it will be visible, and the greater your chances will be for seeing the second planet in our solar system.
Venus is the third brightest object in the sky, right behind the Sun and Moon. It shines at magnitude -3.9. Remember, the lower the number, the brighter the object is, and the brightest stars are about magnitude 0. The dimmest stars which can be seen under dark skies by the naked eye are about magnitude 5; 100 times dimmer. this means Venus is 2.5123.9 or over 36 times brighter than the brightest stars. It should be visible for an hour after sunset, even in the twilight of the western horizon.
This is the planet which has a mass and size most like the Earth, but we would hardly find it a pleasant place to stay. The atmospheric pressure on
Venus is 90 times what it is on Earth, the air is rampant with sulfuric acid, and it is hot enough to melt lead. It's sweltering heat and crushing pressures make this planet, named after the Goddess of love, is very much like a Hell. Perhaps the tribute is fitting.
The
surface temperature of Venus is 470oC (880oF), twice as hot as a home oven.
Due to the fact Venus does not have an ozone layer, it never developed oceans.
Because Venus never developed oceans, it was caught in a run away green
house effect, turning that planet into a scorching desert.
The atmosphere is composed of nearly all carbon dioxide, with some nitrogen, and various acids (including hydrochloric and sulfuric acids) filling in the recipe. At the surface of Venus, the air is only 1/10th the density of water. If you could withstand the poisonous atmosphere, the crushing pressure, the acid rain, and the heat, you could strap wings to your arms and fly.
No matter what kind or size of optical telescope you use, you cannot see below the cloud surface of Venus. This was once thought to prove the existence of dinosaurs on the planet. The argument went something like this. ''I cannot see beneath the clouds of Venus" Therefore, there must be a lot of rain there. "What does rain cause?'', why swamps, of course. "What are in swamps?", Well, dinosaurs, naturally. It was this line of argument which was used as an example of faulty reasoning by my father throughout my childhood. It remains, to this day, one of my favorite stories of Venus. The clouds of Venus exist in three layers (all laying much higher than the clouds of Earth), and although they block out all light from above, the air at the surface of Venus is very clear.
The planet itself is made from similar materials as Earth. It is
95 percent the size of Earth, and has a similar density. Venus rotates backwards
(east to west), as seen from above the north pole. This is a fact which
was not known until 1962. It seems possible that the Earth is the reason
for this particular behavior, although Venus seems to rotate too slowly
for this to be the case.
The next stop in our extra terrestrial journey is known as Bode's nebula. It is a spiral galaxy also known as M81, very similar to our own Milky Way galaxy.
It shines at magnitude 6.9 (about 6 times dimmer than the dimmest stars). M81 appears 25 arc minutes (nearly 1/2o) across; this is nearly the diameter of the full moon or Sun as seen from Earth. Look for it just beneath, and to the west of the north star, Polaris. If you draw a line in the Big Dipper from where the handle meets the pot to half way in between the two furthest stars in the pot, Bode's nebula is in the same direction, nearly that same distance away from the Big Dipper.
Clear skies, and good viewing.
James Maynard is head of the astronomy department at Earth Treasures in Keene, N.H.
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