Thursday, July 9, 2009

Lunar and Solar Eclipses

We had a lunar eclipse on July 7 and there's a solar eclipse on July 21. The lunar eclipse was only visible from the western U.S. and points further west into the Pacific, but the next one on August 5-6 will be visible on the east coast, as well (in the evening just after sunset). The solar eclipse will be visible in China but not in the western hemisphere.

A lunar eclipse occurs when the earth is directly between the sun and the moon, thus blocking any direct solar radiation. This leaves the moon illuminated only by "earthlight", which makes it glow an eery red. This is because the bouncing back and forth through atmosphere causes the shorter, bluer wavelengths to be absorbed, leaving the longer red wavelengths.

A solar eclipse occurs when the moon is directly between the sun and the earth. Since the moon's orbit is not right on the ecliptic plane (the plane on which the earth revolves around the sun), this doesn't happen every month. You can guess the time of an eclipse (lunar or solar), however, by looking at a calendar that has both the date and the time of the full and new moons. A lunar eclipse only occurs during a full moon and a solar eclipse only occurs during a new moon because those are the only times when the moon crossing the ecliptic plane coincides with the earth or moon blocking the sun.

There are many solar and lunar eclipse calculators online. NASA has a good one:

Solar Eclipse:

And this one comes from the Naval Oceanography Portal:

Lunar Eclipse:

As a rule, partial eclipses are more common than total eclipses and lunar eclipses are more common than solar eclipses. I've seen several total lunar eclipses, but only two partial solar eclipses (I would have seen a third one when I was a kid, but heavy cloud cover hid it).

In addition to total and partial lunar eclipses, there are also "penumbral" eclipses, in which the moon darkens a little from the earth's shadow but not much as in a partial/total eclipse. Both this month and next month's eclipses are penumbral.

Thursday, July 2, 2009

Mars and Venus and Jupiter oh my!

—I set the alarm for 03:30 this morning to do some sky watching at a different time. One of my first goals, early in my astronomical career, is to view all the other 7 planets as soon as possible. With only Saturn under my belt, there was much to accomplish!
—So the alarm went off and like any normal work morning, I drug my butt into the bathroom and splashed water on my face. Then I put in my contacts, donned my shoes, and went out for an early morning stroll to my viewing area. To my delight, not only was Jupiter shining down from high above, but both Venus and Mars were up in the East! So off to the house I ran to grab my scope and case.
—There were some seriously disturbing sounds coming from further down the hill from my observation area that I have yet to determine what they were. It sounded like the noise upset squirrels make, on an amp, and echoing. AND there were two of them talking to one another. Fortunately for all involved, the noises did not come closer and I was left happily alone.
—Note on the weather. It was in the lower 60’s, low humidity (YAY!) and a slight breeze. It was cool enough, I put on a long sleeve shirt.
—Scope set up, lens cap off and eye piece in, what to look at first? I go with Jupiter which is high in the sky. Jupiter was spectacular through my 26 mm EP, seems like I could see two moons? Curious as I am I can’t linger and so I then point the scope over to the Eastern horizon and gander at Mars, which proves to be a disappointment overall. Then down a little a little to Venus which a: was plainly visible to me standing up, but was hiding amongst the tops of the 6 foot tall grass in my field, and B: had a huge diffraction spike. GGrrrr. I could see enough to tell there was a little more than half of it visible.
—So out with the 26mm and in with the 6mm and back to Jupiter. This time I could distinctly see two bands on Jupiter. I hovered over it quite a bit trying to fine tune the focuser (Which I have determined I hate). Truly a grand site Jupiter is!
—Then back to Mars which again even in the 6mm EP was nothing more than a tiny orange-ish disk. Wondering to myself if I will be able to make it bigger with a 12″ scope? Or is it because Mars is so far away right now? So many questions.
—Then back to Venus! The diffraction spikes were even worse in the 6mm EP, but at least it had cleared the grass and it was a sharp spiky object lol. I’d like to see it high in the sky. Unsure how long it will be until it is higher again.
—After Venus through the 6mm EP I wanted another peep at Jupiter. To my dismay it was now behind the tip top of a tree to the South even though I could see it clearly standing up. Dang it anyway! So now I know that the first concrete pad I poured is a bit to close to the tree to the South. Going to have to pour another pad soon…
—I then pulled out the 17mm EP and took a look at a blurry spot just to the east of Mars. Turned out to be a spectacular open star cluster. Anyone know what one I was looking at right before sunrise? While staring at that heavenly body, Sol decided to start peeping above the horizon. My my 90 mins went by fast! Then I noticed that Mercury had risen! Could I have first light on 4 planets in the same night? Nope, no way. It was way down in the grass, and I couldn’t begin to get to it with the scope. Going to go weed that grass today, wish me luck…
—I decided then to pack it up and head back to bed. I got first light on three planets and one star cluster. All in all a very productive 90 mins in the wee hours of the morning!

—Things I learned

1: I need my lap top there with me so I can have Stellarium at my finger tips. This is going to require a portable power supply or 200 feet of extention cords…

2: My focuser is awful. Anyone suggest a good 1.25 focuser?

3: To much tall grass around my viewing area. Can you say weedeater?
Blog Directory
Top Blogs EatonWeb Blog Directory RSSMountain

Free Blog Counter
Poker Blog