Wednesday, January 19, 2011

Rocket Launch Visible from SoCal Thursday Afternoon

From an article in today's OC Register:

"The largest rocket ever to be launched from the West Coast blasts off Thursday afternoon with a secret payload from Vandenberg Air Force Base, and the contrail should be visible from Orange County.

The unmanned Delta IV Heavy Launch Vehicle at 235 feet is 51 feet taller than the space shuttle and its propellant tank on the launch pad.

It's scheduled to soar into space at 1:08 p.m. on what should be a mostly clear, windy afternoon. Orange County residents who look to the northwest should be able to see the white contrail of the rocket.

'It's the largest vehicle ever launched from the West Coast, including the Titans launched in 2006,' said Vandenberg spokeswoman Jennifer Green. 'Definitely, you guys might be able to see this one.'

Read the rest of the article here.

Tuesday, December 21, 2010

Lunar Eclipse 2010 Video

Sadly here in southern California we missed out on the lunar eclipse due to the cloudy skies! :-(

If you're curious to see how the whole thing turned out, Florida amateur astronomer William Castleman stayed up very late and had clear views. He made this excellent video. Enjoy!

Winter Solstice Lunar Eclipse from William Castleman on Vimeo.

Friday, December 17, 2010

Two Profound Facts about Lunar Eclipses

(This is a follow-up on my earlier post, "Lunar Eclipse 2010".)

1. Once the Moon enters the central portion of Earth's shadow, it will be bathed in red-orange light. Why is that? Besides being very unusual and pretty, the cause of this is actually profound: that orange-red color is the light cast by the sum of all sunrises and sunsets happening on the Earth at that moment.

Don't follow what I'm saying? Here's a video I threw together:

2. Because the Moon is entering the Earth's shadow, it's a rare chance to directly observe the spherical shape of the Earth. While you've certainly never doubted the truth of the fact that the Earth is round and not flat, have you ever really sought proof for it? Unless you plan on a voyage to interplanetary space anytime in the near future, lunar eclipses are the most visually-arresting demonstration of the fact.

Incidentally, the ancient Greeks were the first to realize Earth's shape (and systematically compile the other evidence for it as well). Sort of turns the old "In 1492, everyone told Columbus he'd fall off the face of the Earth!" claim on its head! If true, those must have been some uneducated people, even for their own time.

For an explanation and schedule of the eclipse, see my earlier post, "Lunar Eclipse 2010".

Wednesday, December 15, 2010

Lunar Eclipse 2010

(For my blog post "Two Profound Facts about Lunar Eclipses", click here.)

Mark your calendar!

There will be an eclipse of the Moon on the evening of Monday, December 20, 2010 and lasting into the early hours of Tuesday, December 21, 2010. This eclipse is especially well-visible from North America, and a lunar eclipse won't occur again until April 2014. (The last one occurred in August 2007).

This event is best-timed for people living on the West Coast. Here is the schedule (times listed are Pacific):

10:30pm - the Moon begins to enter the Earth's shadow
11:40pm - the Moon is completely covered
1:00am (Tuesday) - the Moon begins to emerge from the center of the shadow
2:00am - the Moon has completely left the Earth's shadow, eclipse over

(If you're in North America but somewhere other than the West Coast, simply adjust for your time zone. For example, in New York City, the eclipse won't start until around 1:30am Tuesday. For Chicago, the eclipse won't start until around 12:30am Tuesday.)

What is a lunar eclipse and why do we see it?

A lunar eclipse occurs when the Full Moon passes into the shadow of the Earth. Since outer space is black, we don't usually see Earth's shadow or even realize that it has one. But it does--for the same reason you have a shadow when you're standing in bright sunlight.

Every couple of years, the Moon's orbit and Earth's orbit line up just right such that the Moon actually goes into the Earth's shadow, which makes it seem as if the Full Moon is disappearing. Here's a diagram:

As a result of this, here is what we see from Earth (see time-lapse video below). As can be seen in the video, notice that oddly, as the Moon approaches the very center of the shadow--where you might expect it to get darkest--it actually begins to turn reddish-brown instead.

In my next post, I'll attempt to explain why that is, and you'll learn two reasons why I think lunar eclipses are so worth checking out: Click here to read it.

Wednesday, August 11, 2010

Perseid Meteor Shower Peaks Thursday Night

A meteor streaking across the sky.
Photo credit: Nick Ares, Wikimedia Commons.

Meteors, sometimes called "shooting stars", are more common than most people realize. So long as skies are clear and dark, even on ordinary nights there are an average of 2 meteors per hour.

Meteors start out as tiny bits of rock floating in space. Earth's gravity attracts these bits of rock, causing them to enter our atmosphere and fall toward the surface of our planet. Since they have such a long way to fall, they reach speeds of hundreds of thousands of miles per hour. At speeds like that, the air around them actually causes friction, and so each bit of rock and the air around it heats up. Voila, that's what you're seeing when you see a meteor! (Most of them are so tiny--about the size of a grain of sand--that they actually vaporize before they get anywhere near the ground. Nonetheless, they and the air around them glows so much that you can easily see it as it falls.)

Every few weeks or so, the Earth comes near lots of bits of rock that have floated away from the tails of various comets in the inner solar system. When that happens, we have many meteors fall to the Earth at one time--usually over the course of one or two days. This is what we call a "meteor shower". Every August, right around this time, we have one of the best annual meteor showers, when for one night, about 60 meteors can be seen per hour. (Perhaps the word 'shower' is a bit of an exaggerated name--if a droplet of water per minute come out of your faucet, you'd call that a 'trickle' and not a 'shower'--but that's just what we call these events.)

There are meteor showers about once every 4-6 weeks, but some are better than others depending on the year. The August meteor shower, known as the Perseid meteor shower, is one of the most predictable ones. That means that it may not be the most spectacular shower (others can have hundreds of meteors per hour), but it's a decent show, and it's consistent. Other showers deliver numbers much higher than that some years, but in other years are much, much lower. For these showers, the number of meteors per hour are very hard to predict.

This year the Perseid shower reaches its best on the night of Thursday, August 12, though you can still expect to see some meteors on the nights before and after the peak. Either way, all you need to do is find a place away from city lights (especially street lights), let your eyes adapt to the dark, and lay back on something comfortable with your head to the sky. If the shower delivers, you should see about 60 meteors per hour, or an average of one every minute.

Here are some news articles containing further information:

"Perseid meteor shower will light up night sky this week"

"OC sky's alive with meteors"

Monday, June 28, 2010

In Case You Missed the Eclipse...

Here in Orange County, a layer of coastal fog prevented anyone from seeing Saturday morning's partial lunar eclipse.

But lots of other people throughout the western United States, as well as eastern Asia, the Pacific Islands, and Australia, were treated to the event. One Orange County man, Dave Kodama, headed out to the Orange County Astronomers' private observing site located in the nearby desert, far away from city lights and rarely covered by clouds. There, he got an unobstructed view. He took this spectacular image, showing the Moon setting while still in the Earth's shadow. (If it looks far larger than it ever appears to your eyes, that's an effect of the telephoto lens he was using, which makes distant objects appear much larger than they actually are).

He also made the following video of the eclipse, from just before it began, to when the Moon starts to set (probably about 2 hours). Watch as Earth's shadow descends over the Full Moon:

One aspect of this eclipse that made it unique for observers in western North America was the fact that it occurred when the Moon was approaching the horizon. As anyone who has ever observed a rising or setting Moon knows, the Moon appears larger when near the horizon (a phenomenon known as the "Moon illusion"). It may surprise you to learn that the precise reason for this is still unsettled by scientists. The often cited notion that "you are able to compare it to objects of known size along the horizon", an instance of the optical illusion known as the "Ponzo effect", is considered inadequate by many scientists. But we can be sure it is definitely an optical illusion, and not some kind of magnification: witness the fact that the Moon appears the same size through a given telescope whether at the horizon or at the zenith.

Friday, June 25, 2010

Partial Lunar Eclipse!

You might be interested to know that there will be a partial lunar eclipse very early on Saturday morning (June 26), beginning at 3:17AM Pacific Time, and lasting until moonset, about 2 hours later.

What is a partial lunar eclipse?
A lunar eclipse occurs when the Moon passes into the Earth's shadow. During a lunar eclipse, as the Full Moon passes into the Earth's shadow, it begins to look like a part of it is missing--almost like a bite was taken out of it.

If the eclipse is total, the Moon gets completely covered by the Earth's shadow. Once it reaches the central part of the shadow (usually an hour and half into the eclipse), it will begin to glow red, for reasons having to do with sunlight bouncing off the Earth's atmosphere. But this eclipse is only partial, meaning that the Moon won't get completely covered by the shadow, so we won't see that this time around. Instead it will look like this:

What time should I look?
You're going to have to get up really early. The eclipse begins at 3:17 AM Pacific Time, and lasts until moonset, which for us tomorrow is around 5:12AM. 4:38 AM is the moment of greatest eclipse; at that point 54% of the Moon will be covered by Earth's shadow.

Is it worth getting up this early? What should I expect to see?
You should expect to see a portion of the Moon "missing". Since it's not a total lunar eclipse, you won't get to see the Moon enter the reddish glow of the Earth's inner shadow. Some people don't find partial lunar eclipses that interesting, because it does just look a little bit like a crescent moon, and you can see a crescent moon twice a month.

But if you enjoy astronomy, you will find this event interesting. Here are three reasons why:

1) This missing portion of the Moon isn't a lunar phase, like a crescent moon. We see a crescent moon twice each month because of the changing angle at which we're looking at the Moon as it goes around the Earth. During a lunar eclipse, the Moon's phase is at first full; we're seeing its entire face lit up by sunlight. So when a part of it suddenly goes missing in a matter of several minutes, you're actually getting to see the Earth's shadow! It's not just that you're looking at the Moon from a certain angle.

2) Lunar eclipses are a great opportunity to get to directly observe, with your own eyes, the fact that the Earth is a sphere (ball), not flat. How do we know? Simply notice the shape of the Earth's shadow as it is cast on the Moon: it's curved! In fact the ancient Greeks were the first to pay attention to this fact and realize that the Earth is a sphere.

3) For us here in western North America, Saturday's eclipse will occur when the Moon appears very large! This is because for us the eclipse will be occurring as the Moon is setting. You have probably noticed that when the Moon is rising or setting, it appears much larger than it does higher in the sky. (This is an optical illusion, by the way.)

Is it dangerous to look at?
No, not even slightly. Lunar eclipses are not dangerous. Solar eclipses--when the Moon passes in front of the Sun--require caution, but only because staring at the Sun is dangerous in general. (During the moments before and after a solar eclipse is the only time you are likely to accidentally stare directly at the Sun. This is why they make special "solar eclipse glasses," to protect your eyes.)

How often do lunar eclipses occur?
Lunar eclipses are much more common than solar eclipses. Lunar eclipses occur about once a year, though not everyone gets to see them, depending on the time the eclipse occurs. And as you can see with this eclipse, not every lunar eclipse is total. The last total lunar eclipse visible in North America was Feb. 21, 2008, and the next one will be this Dec. 21, 2010. You can find more information about when they will occur here.