27 May 2012
Did you get a chance to see the eclipse last week? Hope so! Want to see another next week? Hope so!
Whereas the Moon crossed the disk of the sun last week, next week Venus will try its hand at passing through it. Technically it won't be an "eclipse" as we know them. "Transit" is the astrospeak word we use for it. And unlike a solar eclipse which can happen somewhere on the Earth one or two times a year, this Venus transit will not happen again for... well, for the rest of your life. Here's what's going on.
Those who have been tracking brilliant Venus for the last several months may have noticed her getting lower and lower in the sky at sunset. That is because Venus is on a faster, inner orbit around the sun. Right now the Clouded One is about to pass in front of the sun and on to the other side. The Evening Star is on its way to becoming the Morning Star.
But this time is different. Whereas Venus normally passes uneventfully just above or below the sun, on this pass the planet will pass directly in front of our star.
So far Venus is acting very much like the Moon did last week, slowly passing through the sun's disk. But Venus is very much farther away than the Moon and will be able to cover precious little of the bright orb. But you can see it.
Do you have access to a telescope with a solar filter? If so, you can see the transit with no problem at all. But you absolutely must have an appropriate filter. Looking at the sun with a telescope without a real solar filter could mean blindness. It isn't worth it.
Do you have a pair of those solar glasses from the eclipse? You might be able to see Venus with those, as well. That will depend on how sharp your eyes are. Good eyes should be able to discern the small dot of Venus. Bad eyes? No guarantee.
The exact time of the transit for the southern California area will be Tuesday, June 5th. It will start just after three in the afternoon and last until sunset. The whole transit itself lasts over 6 hours, but the sun dips below horizon long before Venus reaches the other side of the sun.
Just as for the eclipse last week, Oceanside Photo and Telescope (http://www.optscae.com/events/transit/) will have solar glasses for sale and - weather permitting - telescopes set up out front for a more up-close and personal viewing.
Why should you see this transit? After all, the last one was just years ago in 2004. Well, because of the orbital dynamics of our two planets, this transit will be the last until 2117. You want to mark "Venus Transit" off your bucket list? This is your only remaining chance.
13 May 2012
Got anything going on next Sunday late afternoon? No? Well, don't plan anything just yet. There's a solar eclipse coming and you're invited.
On Sunday, May 20th, starting at about 5:30 PM, the Moon will begin to cross in front of the sun as it sets in the west. It will cover as much Sun as it can by about 6:40, then move past it and allow the sun to finally set alone. It won't be a total eclipse for us, nor will it be a total eclipse for anyone. Let me explain why, and then tell you how to see it.
We all know that the Moon orbits our planet about once a month. Its orbit is almost on the same plane as our own orbit around the sun, meaning sometimes the Moon will move right exactly in front of the sun, blocking its light and blessing us with an eclipse.
The immediate problem for us in Southern California is that we are off the main track for the eclipse which passes through northern California, Nevada, Utah, Arizona and New Mexico.
From our position on earth, the Moon will appear to pass through the sun, but just off center. That means the best we will get is a crescent-shaped sun as the Moon still manages to bite out a substantial chunk.
So where can we see the full, total eclipse that we have seen so many times on calendars and astronomy magazines? Nowhere on the planet. Here's why.
Remember the big, extra bright Moon we had a week ago? It really was slightly bigger than the usual full moon. That is because the Moon was at what we call perigee, the nearest in its orbit that it comes to earth. You see, the Moon's orbit is not the perfect circle; it is slightly elliptical, or oval-shaped. That means sometimes it is closer (perigee), then two weeks later, on the opposite side of its orbit, it is at its farthest (apogee).
Here's my point. Around May 5th the Moon was closest, which is why the Moon was so big. On May 20th it will be at its farthest, which means it won't be able to cover the whole sun like it usually does. So even those people who live on the path of the eclipse, in direct line with the Moon and Sun, will only see - at best - a gigantic hole in the sun with an extremely bright ring of light around it as the Moon tries to cover the whole sun, but cannot.
But even a partial eclipse is worth a look. There are several ways to do it. One is to use a pair of eclipse glasses. You can get these online or at Oceanside Photo and Telescope (OPT). OPT will also have telescopes out on the 20th with solar filters so you can get up close and personal with the eclipse, assuming the weather agrees. (Go to www.optcorp.com for more info.)
Can't do that? Sky and Telescope Online has an entire article for observing an eclipse safely. Go to skyandtel.com and type "Watch Partial Eclipse" in the Search box. Then go to the article.
One cool thing you can do with no equipment at all is to look at the shadow of any leafy tree. Really! Around the leaf shadows you will see countless crescents. They are tiny images of the eclipse caused by the way light travels through tiny holes between the leaves.
However you can view it, get thee outside and observe! We won't be getting another for a long, long time.