FirstLight Astronomy Club

33°29.6'N / 117°06.8'W / 1190 ft.

Mercury is Inferior!

Has your body ever suffered from inferior conjunction? Don't know? Well there is one body experiencing that phenomenon - today as a matter of fact. It is tiny Mercury. But what exactly is this condition, and do we have to worry about catching it?

Inferior conjunction is merely a term which tells one about the position of one body with respect to two others. Some readers may recognize the term "conjunction" from phrases like "The planets were aligned; they were in conjunction." It is a term derived from the Latin word meaning "connected," which is how two heavenly bodies look when they are lined up in the skies.

In today's event Mercury lines up with the Sun, passing in front of our star, or as close as it can. The two are in conjunction, but why the "inferior"?

Mercury and Venus, being on the inside lanes of our solar system race course, can actually line up with the Sun twice, once as they pass between us and the Sun, and once again on the far side as they pass behind our star.

The inside alignment is called inferior conjunction. That more distant alignment is called superior conjunction.

The outer planets (Mars, Jupiter, et al.) only get to be "in conjunction" with the sun - no inferior or superior is involved. They can only be aligned with the sun when on the far side of the sun; they never come between us and our star.

And when those outer planets happen to be on the opposite side of our planet when compared to the sun we get yet another term; those planets are then in "opposition."

You may be curious as to why little Mercury and Venus do not often actually pass directly in front of the sun when they are in inferior conjunction. (Mercury missed doing so today as a matter of fact.) It is for the same reason that the Moon, when it passes in front of the sun every month, does not always give us an eclipse.

The orbits of Mercury and Venus compared to our orbit are not perfectly lined up. Sometimes the planets pass just "below" the sun, at other times they pass "above." Occasionally they do pass right in front of the sun, appearing as tiny dots crawling across that brilliant face. That is called a "transit."

Had your fill of new astronomy terms? But I didn't even mention western or eastern quadrature, or greatest western or greatest eastern elongation. Or eclipse or occultation or the ever-amusing syzygy! Alas!

All right then. Maybe we can line them up for a future article. Until next time, clear skies!

Test Time! (Fear not!)

That dreaded time of the school year is upon us; the time that fills teachers and administrators with angst and causes untold numbers of children to roll their eyes to the sky while sighing, "Do we have to?" The state tests are here again.

Let's try and counter the unease many of us feel and take a fun and stressless quiz of our own. Only three questions and it's not even graded. And there is a bonus! You will be more learned because of it. Ready? Grab your sharpened Number 2 and let's do it.

Question 1: We live in a huge collection of billions of stars. What is it called?

A) The Milky Way
B) The Solar System
C) The Orion Nebula
D) Hollywood, CA

Regular readers here will nail this one instantly. It is the Milky Way, of course. Our galaxy, well over a hundred billion stars strong but organized nicely into a barred spiral shape, is our home.

The solar system is, of course, our local group of planets and debris orbiting the sun. And the Orion Nebula is that star nursery about 1200 light years away in the constellation Orion.

Question 2: What is the origin of our atmosphere's oxygen?

A) Asteroid and comet bombardment
B) Eons of plant life
C) The decomposition of ocean water
D) Walmart

This one isn't so easy but it is keenly important. Bombardment gave us extra rock material to be sure, and is probably responsible for a lot of our water, but not for any significant amount of oxygen. And water itself can break up into hydrogen and oxygen but is definitely not the source of our life-preserving amount of oxygen.

Plant life is the culprit. Early on this planet had essentially no free oxygen. The plants through photosynthesis slowly - and I mean slowly - immersed our planet in the gas. Much was taken by the rocks and oceans but some of it was eventually pumped into the atmosphere, perfectly timed for the arrival of the more complex animal life on land. A miraculous bonus was that some of this oxygen got converted to ozone to protect us from the nasty UV rays from the sun.

Question 3: Why is the liquid magma below us still so hot?

A) Radioactivity
B) The sun warms it.
C) Our magnetic field adds heat to the core.
D) Someone left the iron on.

After 4.5 billion years our insides are still hot as where the devil lives. Why? The big reason is that radioactivity from unstable elements keeps it real hot and the crust traps that heat. Result? We have a molten inside upon which our crust floats. The upshot is that we still have plate tectonics after all these years. Go Earth!

Do well? Of course you did! Until next time, clear skies!
Temecula Valley High School / Temecula, CA · Some images © Gemini Observatory/AURA Contact Me