30 Nov 2008
There is an utterly brilliant star rising over the southeastern skies in the late evenings below Orion. This is not Venus, the usual suspect, or even Jupiter, or any planet for that matter. It is Sirius, the headlining star for the constellation of the Big Dog, Canis Major.
It is not just its brilliance that makes it stand out; there is also what appears to be a twinkling of color emanating from it. Why is Sirius so very bright and whatâ€™s up with that multicolor twinkling.
Sirius belongs to the stellar spectral class A. In astrospeak, that means it is big and nasty and hot and dangerous but not too big and nasty and hot and dangerous. It is only a couple times bigger than our sun, a bragging point to be sure, but Sirius is not big enough to belong to the Death by Supernova club.
It will, in the next eon or so, graduate to a red giant, only to whimper out as a white dwarf, a fate similar to our sunâ€™s.
What makes Sirius so bright is its proximity. It is a mere 8.6 light years away, essentially down the street. This short distance allows it to be the brightest star in our skies, and, from our vantage point in Southern California, the closest visible star. (Alpha Centauri, at 4.4 light years, is visible to people more southerly than we.)
What allows it, and all other stars, to twinkle is not a property of Sirius, but of our atmosphere.
Our ocean of air is one turbulent, violent place with hot air rising and cool air sinking all around - and not just at the humungous cloud-size scale. There are micropockets of air out there of varying temperatures. Our atmosphere is no smooth, tranquil place.
Here is the twinkle connection. When light travels through different substances, even if it is the same substance at different temperatures, it can change direction - it is refracted. You have seen this when light passes through eyeglasses; the light's path is bent. Even the different colors within light get redirected at different angles.
Bottom line? A nice, bright, passive beam of light from Sirius gets throttled when it goes through our turbulent atmosphere. The light seems to bounce around and can even get separated into its component colors.
You see now why it is desirable for astronomers to get their telescopes as high above the disturbed atmosphere as possible, even sending them into orbit above the planet.
Though not conducive to good science, a brilliant, twinkling Sirius does appeal to the poet in us. Go out and see it in the next months in the southeastern skies as it follows Orion. It's a dazzler.
16 Nov 2008
When I was in high school I used to go to dances. Not to dance, mind you - I was awful. I would just hang out with my friends in the bleachers and be entertained by the dancers on the gym floor.
I do the same now, only the dancing bodies I observe are in the skies. You can join me in the bleachers in the next several weeks as I watch two heavenly dancers, Jupiter and Venus trip the light fantastic.
In the southwest skies after sunset you will notice two extra bright "stars." The brightest by far is Venus, the dimmer is Jupiter. They are both on a similar course around the sun as we. Only Venus is on an inside fast track, and Jupiter is way out in a slowpoke lane.
Those track assignments unwittingly result in the dance we can see in the next weeks. Venus is currently making a turn around the sun trying to lap us again on the inside. She will, but it will take several more months to do it.
Her attempt to catch up with us will make her appear higher and higher in the sky each evening as she rounds the sun. Now hold that thought.
Jupiter is so slow that our own planet is now about to traverse to the opposite side of the sun as the Big Guy, making him appear to get closer to the backside of the sun in our evening skies.
Put these to movements together, Venus' uphill climb and Jupiter's downward fall and the two will appear to be getting closer to each other daily, passing by each other by the end of the month.
You will know when they are at their closest because a young crescent chaperone Moon will be right there on the dance floor to break them up on the last day of November, and the first of December.
There really is no need for the Moon to police their dance moves. They are nowhere near each other in reality. Jupiter is actually almost 450 million miles away from the bright temptress, way too far be entranced by her charms.
For those of you with telescopes, these are your last days to see Jupiter and his satellites for a while. They will soon disappear into the glare of the sun. But you can watch Venus as she approaches us, getting larger in the field of view as days go by.
Venus and Jupiter won't put on this nice of a display until 2010/2011. So if you have a chance in the next weeks, go sit up in the bleachers and be entertained.
Until next time, clear skies!
02 Nov 2008
Looking up into the early evening skies tonight, in the southwest, one may see nothing but some stars, a moon, and a couple planets. But it won't take more than a minute for those who can see patterns to notice that there is something more going on here.
Right after sunset, in the 5 o'clock hour, look to the southern skies and see that the sun, Moon, and two bright dots form a sort of line across that part of the sky. The two bright dots are the superbright Venus, and dimmer Jupiter, nearer the Moon.
Notice also, in the next couple days, how the Moon seems to extend that make-believe line out across the southern skies. And, if they were bright enough, you would observe that both Neptune and Uranus are on that same line, over towards the southeast.
This imaginary line that circles the earth is called the ecliptic. Hugging this line one can find all the planets, the sun, and the
Moon. You will never find any of these solar system objects straying more than a few degrees from it.
What is this line? And what does it mean?
Pretend your favorite crazy uncle is in the middle of a lake, just bobbing gently up and down, dressed in an oversized, inflatable yellow bathing suit and pretending to be a sun. Around him at various distances are tiny family members, including you, swimming around him. None are flying overhead, none are diving below; they are all stuck on the same flat plane, the surface of the lake. From your perspective as a wannabe planet, your uncle and all the other wee swimmers around you can all describe a giant encompassing circle.
That is analogous to what our solar system is like. Only the planets are not floating on a lake to keep them all nicely leveled. But they are all on a disk-like plane on their trip around the sun. Why are they all that way? Here's what we think.
All those planets residing on the same plane going in the same direction is strong evidence that they all formed from the same whirling cloud of dust and gas sometime in the distant past. We see similar flattened disks choked with dust and gas around distant baby stars implying planets may be forming there now as you are reading this.
That ecliptic is not just pretty cosmic geometry; it is evidence for how it all started.
Until next time, clear skies!