FirstLight Astronomy Club

33°29.6'N / 117°06.8'W / 1190 ft.

Reviewing basics of astronomy

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Being steeped in the sciences can cause one to lose touch with just how "unsteeped" most other folks are. A couple of recent comments and questions I heard compel me to revisit some of the more simple aspects of astronomy. Let's have a little Astro 101 lesson today, and we will use a convenient triangle in the sky tonight to teach us.

Going out this evening around 9 o'clock hour, look overhead. There see the Moon. Assuming you are facing south, see directly above the Moon a star called Regulus. Just to the "left" of Regulus is the bright, pinkish Mars.

There in the that triangle are three important ingredients of the skies above us. Let's look at each to get a big picture.

The Moon is a satellite of this planet of ours. It orbits around Earth once every 30 days. Not many understand that it really does move though the skies. Come back tomorrow and it will have moved further towards the east in its circuit.

Now just as the Moon goes around the Earth, Mars and all the rest of the planets are orbiting the Sun in a collection called the solar system.

All eight of us orbit in the same direction, but we all go at vastly different speeds; the inner planets are faster, the distant outer planets much slower. Planets orbiting at different speeds is why it seems the planets are moving all over the skies through the year. Jupiter was here for months but finally went behind the sun. Venus will be heading down in the evening skies for the next weeks. Mars and Saturn will be dancing around up there for spring and summer. No wonder the Greeks called them wandering stars. See for yourself how Mars moves away from Regulus over the next months.

Regulus is one of those other stars, the "fixed" stars, the vast canopy of twinkling lights up there, but not a part of our tiny system of planets. Yes, our own sun is a star, but all that you see up there - from bright Regulus to the faintest pinpoints of light - are all a part of an enormous disk of stars called the Milky Way, our galaxy. This galaxy of ours has well over 100 billion stars spread throughout it and is over 100,000 light years across.

And our Milky Way galaxy is only one of hundreds of billions in the universe, a topic for another day.

Here is a wee recap: We have a Moon, a satellite which goes around us once a month. We, along with Mars and six other planets, are orbiting the sun. Regulus is but one of a myriad of stars including our sun orbiting in a the vast collection of stars called the Milky Way.

When you see the Moon and Mars and Regulus up there tonight, see the Big Picture, too.

Saturn swinging by for a visit

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With Jupiter, the king of the planets, about to ride off into the sunset in the next weeks, it is time we turn our attention to arguably the most beautiful of the planets, Saturn.

Saturn is currently at what astronomers call "opposition." When a planet is at opposition it is on the opposite side of the earth as the sun is. As the sun sets in the west, Saturn rises in the east. This happens because we, on our inside track around the sun, are passing Saturn in our orbit. We have come between the planet and our star.

A simple understanding of geometry will tell you that opposition is when we are closest to the planet we are passing. But even a close approach is a tremendous distance for an outer planet such as Saturn. Its "close" approach is still over 800 million miles away.

This great distance means it will take just a little more effort than finding bright Jupiter and Venus in the west. But it is easy! Ready to try?

Go out in the evening around 9 o'clock and find the Big Dipper in the northeast. It is essentially hanging upside down on the great kitchen wall of the northern skies. Follow the "handle" of the dipper around to the east to a very bright star called Arcturus. Don't stop! Keep going over to the next bright star in the southeast called Spica.

Do you see a golden, star-like object near Spica, just a little to the "left"? That, my dear reader, is Saturn.

But where are the rings?

They are there but being nearly a billion miles away makes seeing them a tad difficult. Do you have a small telescope? Can you borrow one? Do what you can, short of a felony, to get one in the next couple months while Saturn is as close as it is.

What you will see is one of those sights you will never forget. The golden hue of the great gas giant surrounded by its stunning, icy ring system will drop the jaw.

Here's a hint that astronomers use that will help make your viewing experience even better. Do not look at Saturn through the scope as it rises above horizon. The heat from the earth's surface will utterly ruin your viewing. Wait until Saturn is well above horizon and the viewing will be much better.

Saturn is there for the rest of the summer, but take advantage of its close approach and see it as soon as you can.

Until next time, clear skies!

Cool stuff to know about boiling points

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Well, it is spring break for a lot of schools, including mine. But I still feel a need… a need to give a quiz. So how about this week we take a little quiz here. And when I say little, I mean it; just two questions. Don't worry, the answers are either true or false.

Question: If you were on Mars now and could somehow hold a drop of water in your hand, it would boil away in a second.

Answer: Mars is up in the sky in the east in the evening. It is considerably farther away from the sun than we are. It isn't hotter there, it is very much colder on average. So why even ask something so obviously false? Water boiling on such a cold planet is an absurd idea.

Well, actually it is a true statement. A drop of water would boil right off your hand right in front of you. But that is because boiling isn't just a temperature thing. Pressure plays a role here, as well.

We all learn that here on Earth water boils at 100˚C (212˚F). But what most people do not know is that that special temperature is only valid at "standard atmospheric pressure" which is approximately the average air pressure at sea level. Let me elaborate.

Water molecules have a tough time getting away from other members of their clan; they are very attracted to each other. But atmospheric pressure - the pressure of air molecules pounding down on us all - forces them to stay with each other even more. If you give water molecules less pressure, meaning fewer air molecules stomping on their tiny heads, they won't need as much energy to break away into a gas. Thus, lower pressure means it becomes easier to boil.

If you go to the local mountains - where there is less air pressure - water will boil at lower temperatures. Take the liquid water even higher and they need even less energy to overcome the reduced air pressure and the boiling point goes way down. On Mt Everest, for example, water boils at about 68˚C (154˚F).

Now go to Mars. Yes, it is cold there, but there is also only about 1% of our atmospheric pressure bearing down on anything on Mar's surface. That is precious little pressure. So water is not nearly as compelled to stay with its buddies. And there is just enough heat energy there to allow the little guys to escape almost instantly into the Martian atmosphere. Away it boils!

Question: On Earth, a drop of water in your hand boils away in a second.

Answer: Gloriously false. Because of Earth's ideal average temperature and atmospheric pressure, this planet can hold onto a lot of water in all three states - gas, liquid, and solid - all necessary for a life-sustaining planet.

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Temecula Valley High School / Temecula, CA · Some images © Gemini Observatory/AURA Contact Me