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Astronomy

¨  Can I see "Ares" in the sky on August 27, 2005?
¨  I see a flashing red star.  Is that the Eagle Nebula?
¨
  What are the two best stars to look at at 9 p.m. from my telescope?
¨
  Do all planets move in a counter-clockwise direction?
¨
  How do we get pictures of the Milky Way when we're inside it?
¨  Cartes du Ciel software instructions
¨  Will Mars be a million miles closer to Earth in August 2005?
¨
  How far are the planets from the North Star from my backyard?
¨  When is the meteor shower for August?
¨  Why is the northern hemisphere cold when it is closest to the Earth on December 21?
¨
  What will happen to the Earth and planets when the sun dies?
¨
  How much does the Earth's rotational speed decrease every century?

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QUESTION:
I was told I would be able to see 'Ares' in the night sky on Aug. 27, 2005 at 12:30 am.  Have you ever heard of this?

ANSWER from Roger Herzler on 2 September 2005:
I've got two ways to answer this:

1) You're referring to "Aries", the stellar constellation.  It's in the night sky and it's visible during various times of the year.  Based on my position close to San Diego, CA I pulled up a map on http://mystarslive.com/ that shows it high in the sky looking in a southerly direction.  You should give that website a try.

OR

2) You're referring to "Ares", the Greek name for the god of war, AKA "Mars".  Mars is also visible in our night sky right now and is a bright object in the early morning appearing nearly directly overhead or slightly to the east around 5:00AM.

Both of these objects are still visible even though it's after 8/27/2005.  Good hunting.

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QUESTION:
Around 9:00 PM in the southwest I see a flashing red star.  Could that star be the Eagle Nebula?

ANSWER from Roger Herzler on 2 September 2005:
No, unfortunately nebula never look like "stars".  In fact, they look more like blurry "fuzz" with little detail in your eyepiece.  They are never a bright pinpoint like a star.  What you probably saw was a star, or maybe even an airplane if it was flashing a lot.

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QUESTION:
What are the two best stars in the nighttime around 9 PM for my telescope to navigate through?

ANSWER from Roger Herzler on 2 September 2005:
In the northern hemisphere the best star would be the North Star, or Polaris.  It is always out, all night long, and located in pretty much the same spot night after night.

The second star you could pick is up to you and will probably be different from night to night or definitely season to season.  For example, you may choose stars like Sirius, or Capella, or Betelgeuse.  However, they are all in different positions depending on the time of the year (or even the time of the night due to the rotation of the Earth).

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QUESTION:
Can anyone tell me if all of the planets tend to move in a counter-clockwise motion, including the Sun?

ANSWER from Roger Herzler on 23 August 2005:
You're in fact correct - the planets and Sun rotate around in the solar system in a counter-clockwise motion based on what is considered the "north pole" of the Sun.  This motion is left over from the direction the gas and dust was moving during the formation of the Solar System's "accretion disk".

Interestingly, all of the planets except Venus, Uranus and Pluto also rotate on their axes in the same direction.

You can find more information at http://www.solarviews.com/eng/solarsys.htm
and
http://nineplanets.org/overview.html

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QUESTION:
How can we get pictures from a far vantage point of the Milky Way when our telescopes are inside the galaxy?

ANSWER from Roger Herzler on 22 August 2005:
That is an excellent question and illustrates just how tenuous our understanding of the Milky Way actually is.  We assume that it's a spiral galaxy based on the positioning of the arms that we can see under dark skies, and we know what other spirals look like outside of our galaxy.  Ultimately though it is all hypothesis and theory based on researching external galaxies that helps us describe our home galaxy.  We haven't directly observed the Milky Way from the "outside".

The SHORT answer to your question: We can't at this time.

The DESCRIPTIVE answer: We cannot get pictures from outside our galaxy with our current technology.  To give you an idea of the distances we're dealing with just inside our galaxy, according to NASA (http://science.nasa.gov/headlines/y2001/ast01nov_1milkyway.htm) it would take 80,000 years for light to travel from one side to the other side of the Milky Way.  We don't currently have any propulsion technology that even comes close to light speed, so it would take much longer for us to do it. However, we could travel perpendicular the galaxy to see a "top down" view and shorten that time because we wouldn't be going across the galaxy to do it.

Unfortunately, we must add the time it would take to get a meaningful distance away from the Milky Way to accomplish taking a picture and you're dealing with some very long timeframes.  To give you an idea of that distance, take the Andromeda Galaxy (M31) for example.  We can see great pictures of it, but it's 2.9 million light years away from us according to http://www.seds.org/messier/m/m031.html .  That's a LONG way away.

Lastly, consider that getting there is just half the battle.  Transmitting the images back to us would also be constrained by the speed of light and we'd need to account for that as well.

All in all, getting pictures of our galaxy is impossible right now, and impractical for the foreseeable future.  However, I rarely say "never" when dealing with technology and the human spirit.

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QUESTION:
I use "Cartes du Ciel"on a regular basis.  Clicking an individual star results in a list of several terms which I am un-familiar.  Where can I see a description of these terms?

ANSWER from Roger Herzler on 22 August 2005:
Cartes du Ciel is a stargazing star charting application and it's FREE to boot.  These seem to be a helpful links for finding out more about it: http://www.stargazing.net/astropc/ and http://www.ap-i.net/skychart/index.php .

I don't have it installed, so I don't know exactly what terms your discussing.  However, you can find out a lot of detail in its documentation by going to http://www.stargazing.net/astropc/doc/eindex.html .  Maybe you're referring to the symbols such as: Var, Dbl, Gx, Neb, etc.?  Go to the Documentation page.  Those are all listed there.

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QUESTION:
Is it true that Mars will be a million miles closer to Earth in August 2005?

ANSWER from Roger Herzler on 15 August 2005:
There are a number of Internet email chains going around claiming that Mars will be the best view ever later in summer 2005, and even as 'big as the Moon'.  It was as close to the Earth as it will be in 50,000 years back in 2003, but the chain was resurrected for 2005.

It is true that Mars gets closer and farther away as both it and Earth go around in our orbits, BUT it won't be any more of an amazing sight than it normally is when it gets closer to us.  See some of these Internet resources explaining the fallacies of the email chains:

October 2005 Approach
http://science.nasa.gov/headlines/y2005/27may_approachingmars.htm

Details About the 2003 Martian Approach
http://skyandtelescope.com/observing/objects/planets/article_985_1.asp

Current Email Chain Corrected by Snopes
http://www.snopes.com/science/mars.asp

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QUESTION:
From my backyard I can see the North Star straight ahead.  How far is Venus, Mars, Saturn from the North Star?

ANSWER from Roger Herzler on 15 August 2005:
Unfortunately, there is no direct answer to this question because the night sky literally changes every night as objects continue to move around the Sun and through the Universe.  Even the North Star won't be the "North Star" many years from now.

Your best bet is to use a planetarium program or use an online tool to get an updated picture for the day you want to observe on.  You can find a list of those at:

http://astronomylinks.com/cgi-bin/links/search.cgi?query=planetarium
or
http://astronomylinks.com/charts_and_maps/

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QUESTION:
When is the meteor shower for August?

ANSWER from Roger Herzler on 12 August 2005:
The primary meteor shower in August is the Perseids.  In 2005, the maximum is expected on August 12.  See http://skyandtelescope.com/observing/objects/meteors/article_1557_1.asp for more information.

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QUESTION:
Even though the sun is closest to Earth on December 21st, why are we in the northern hemisphere still cold?

ANSWER from Stephanie Wong on 14 May 2004:
This is a common misconception of how the seasons work.  If the distance to the sun were to greatly affect our climate, you might be lead to believe that both hemispheres of the Earth would get summer at the same time and winter at the same time.  This is not the case.

Although at the winter solstice the Earth does come closest to the sun, the increased heating is negligible.  What does matter is the angle at which sunlight hits the surface of the Earth.  Because Earth's rotational axis is tilted at 23.5 degrees, one hemisphere of the Earth is tilted towards the sun during one half of the year, while the other is tilted away.  For example, on December 21, the southern hemisphere is tilted towards the sun and gets more direct sunlight.  The sun is higher in the sky and much of the sunlight is "beamed" straight down.  In the northern hemisphere, we are tilted away and therefore the sunlight we get comes in from a shallower angle and so the sunlight that hits the surface gets spread out over a larger area.  Try using a flashlight and shining it straight down and then at an angle to the floor.  The same amount of light gets spread out over a larger area.  You can also think about the heat of the sun: On a hot summer day, at noon, you can feel the sun just raining down on you, but at sunset, the sun is still there, but it certainly isn't as "strong".

Another effect of the tilt is the length of day in the seasons.  In the winter, the day is much shorter so that overall we have a shorter time to absorb the sun's energy per day.

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QUESTION:
Through the research I have made, I have found out that Sun's lifespan is ten billion years.  Now, the Sun is only five billion years old.  In five bilion years after the Sun blows up and the Earth and the planets are destroyed, will they reform again?  Will life restart again on another Earth?  Maybe we have restarted before?

ANSWER from Seth Shostak on 3 May 2004:
As you already know, the Sun will eventually run out of fuel -- the hydrogen that's deep inside its core that is being converted to helium.  This conversion of hydrogen into helium is just like what happens in a hydrogen bomb, and is the source of the Sun's light.  But as you note, in about another 5 billion years, this hydrogen will be used up.  What happens then?

Well, even though it may seem strange, the Sun will actually swell up like a balloon.  It will get dozens of times bigger than it is now... maybe even as much as 100 times bigger.  It will be a huge, red ball in the sky, and there will be so much heat from this dying Sun that it will boil away all of Earth's oceans.  It will also swallow Mercury and Venus (and maybe even Earth).  Our planet will become sterile -- no life.  After a few hundred thousand or few million years, the Sun will collapse again... eventually, it will become a small, hot ball of gas (about the size of the Earth, actually), and in 50 or 100 billion years, will cool off to become a lump of charcoal.  That's its future.

And because the Sun will never be "normal" again, life on Earth will be gone forever, once the Sun starts to go bad.  Of course, if our descendants are still around in 5 billion years, they may decide to build large rockets, and go find another star that's younger and still normal, and live there.  But 5 billion years is a long time, and it's hard to imagine exactly what life on Earth will be like then -- or whether there will still be any humans!

Seth Shostak
Senior Astronomer, SETI Institute
www.seti.org

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QUESTION:
How much does the Earth's rotational speed decrease every century?

ANSWER from Doug Hube on 26 November 2003:
The length of the day (= the time required for the Earth to rotate once around its axis) is increasing by approximately 0.0016 second per century.

That is, the Earth's rate of rotation is decreasing... its rotation is slowing down.

To complete one rotation on January 1, 2001, took 0.0016 second longer than to complete one rotation on January 1, 1901.

That slowing in the rotation of the Earth is due to tidal friction in the shallow waters of the oceans.

That friction dissipates energy, specifically kinetic energy of rotation.

As Earth's rotation slows, the angular momentum of terrestrial rotation decreases.

To a first approximation, the Earth-Moon system is an isolated system.  Angular momentum is conserved in an isolated system.  Therefore, if the Earth's rotational anmgular momentum is decreasing, angular momentum of another component of the system must be increasing by a like amount.  The Moon's angular momentum of revolution is increasing.  The result is that the Moon's orbital radius in increasing... the Moon is slowly receding from Earth.  The aparent size of the Moon is, therefore, decreasing.  Eventually there will be a time when total solar eclipses will not be possible.

The picture described above was first revealed by comparing records of ancient solar and lunar eclipses with 'modern' (i.e. 18th and 19th century) calculations.  The cumulative effect of the slowing of earth's rotation amounts to a little more than 3 hours over 2000 years.

The Earth-Moon system is dynamically very complex and the summary above represents a smoothed, average model.

Doug Hube
Department of Physics
University of Alberta
Canada

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5 October 2005
 

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