Thursday, June 22, 2006

Sheer Luna-See

It seems that whenever someone gets a new telescope or pair of binoculars, the first thing they want to do is look at the Moon. Many has been the time that I've heard some people say "why don't we wait until it's a full Moon so we can see all of it?" Sounds simple enough... it is a "full" Moon, right? However, that's really not the best time to observe the Moon at all.
Let's talk a little about our planet's one natural satellite. The Moon is pretty big when compared with Earth, a little over 1/4 its diameter (2160 miles/3476 km for the Moon, 7926 miles/12756 km for the Earth). In a very real sense, this makes the Earth/Moon system a double planet; when you compare other planets and their satellites, you find that they are much, much smaller, with Pluto being the one notable exception (and a subject for another day). Our Moon sits at around 238,000 miles/383,000 km from our humble abode, making it by far the closest of our celestial neighbors. At that distance, the Moon covers less than 1° of sky, less than your pinky finger held at arm's length. It seems bigger, but that's just a trick of the eye and mind. Ironically, the Sun also covers roughly the same area. By an incredible coincidence, both the Moon and Sun appear nearly the same size in our skies!
Geologically, the Moon appears to be dead, but it is covered with reminders of our Solar System's violent past; thousands of craters. Amazingly, though, it still gets hit from time to time. As recently as the 1st of May, 2006, astronomers using video equipment caught an impact as it occurred. There are other lunar facts that everyone should be familiar with, such as the fact that the Moon has almost no atmosphere and around 1/6 Earth gravity. It's also naturally a very dark color, almost the color of asphalt; its brilliance comes from reflected sunlight.
Now that we've covered the basics, let's talk about the best time to observe. As I mentioned earlier, many people are tempted to look at a full Moon. While this is fine, the video image below shows pretty much what you can expect to see.

(video image by Robert Little)

The problem with viewing the full Moon has to do with a lack of contrast. Since the Sun is pretty much straight up from the Moon, there are few shadows being cast. It's still interesting, just not very revealing. The best time to view the Moon are the phases leading up to the full Moon, and in particular the smallest ones, the crescent and quarter phases. The phase between quarter and full, gibbous, is good for some observing as well. The following low resolution video images were made on the 24th June, 2004 and show the northern and southern sections.

(video images by Robert Little)
As you can see, there is a lot of detail, and the craters and various bumps and gouges really stand out. The next image was taken on the 22nd of September, 2004. This is a close-up of an almost first quarter Moon. During this phase, the large maria (literally "seas") become visible. These huge, dark plains are actually enormous basins filled with ancient lava that has hardened into a basalt. The best time to observe the maria are quarter and gibbous.

(video image by Robert Little)
In this image, which is tilted 45° to the right, the predominant features are Mare Serenitatis, the Sea of Serenity (upper center), and Mare Tranquillitatus, the Sea of Tranquility (lower center). It was in the Sea of Tranquility that the first Apollo astronauts touched down in July of 1969.
After the first quarter Moon, the phases get progressively brighter until they reach full. Then, the phases go in reverse, from gibbous to quarter and then to crescent and back to new. Of course, most of these post-full Moon phases occur pretty late and go well into the morning hours.
Whenever you plan to observe the Moon, though, it helps to have a good guide. There are plenty of good books out there about observing the Moon. Patrick Moore's classic "The Amateur Astronomer" has plenty of great information. One of the most detailed lunar observing books is "Exploring The Moon Through Binoculars" by Ernest H. Cherrington, Jr. There are some great online sources as well. Draco Productions has a simple online map. A more complex map can be found at Observatorio ARVAL's website.
The Vagabond Astronomer will be outside of Books-A-Million in Mandarin on Wednesday the 28th and Friday the 30th after 8pm both nights. Come on by as we take a long, close up look at our closest cosmic neighbor.

Saturday, June 17, 2006

A Dearth Of Stars

There are certain times of the year when it seems that the sky is just uninteresting. There's a lack of bright stars, easy to find deep sky objects and the constellations themselves just seem faint. Here in the northern hemisphere, this is spring and autumn, obviously reversed for the southern hemisphere.
Yet if we live in a galaxy that has between 100 and 400 billion stars, then why such a dearth? Well, it has to do with the fact that our Solar System is tilted.
The picture below shows the entire night sky, all 360° of it. You'll notice that most of the brighter stars seem to follow a serpentine pattern. That is the actual galactic plane, what we know as the Milky Way itself.

(image produced with Star Atlas v.06b1 by Youhei Morita)

Our Milky Way galaxy is a barred spiral, essentially a flat, spinning disk with a slight bulge near the center and over 100,000 light years across. Our little Solar System is located some 30,000 light years from the center, as indicated by the circle near the top center of the Milky Way map (which, I admit, is based on the best information we have available and is probably still far from accurate. Incidentally, our Solar System would be near the center of the circle, microscopic in this scale. Very microscopic...).

(image by Robert Little)

If our Solar System was aligned so that our Sun's axis lined up with the galactic axis, we'd never want for Milky Way filled nights, and only the view towards our poles would show fewer stars than around the ecliptic (the main plane of the Solar System, the imaginary belt in which most of the planets lie). Instead, our Solar System is actually tilted 62° from the galactic plane itself, almost lying on its side.
(image by Robert Little)

As a result, there are times when our night sky actually faces out through our galactic plane, through less densely populated sections of our local interstellar neighborhood. This is why the stars in the spring and autumn seem to be lacking. That's not to say that it isn't worth still doing; stargazing should be enjoyed all year round. Still, if your wondering why the night sky is so humdrum, just remember we're tilted. It's all in how we're aligned.

Monday, June 12, 2006

Planets In The Western Skies

Friday the 16th of June looks to be promising from a planetary view point... at least the view from the planet Earth. And the excitement begins just after sunset.

(image courtesy of "Your Sky" )

In total, three planets should be visible in the western sky just after sundown; from the horizon up, Mercury, Mars and Saturn. Let's start with the least visible of the bunch, Mercury.
As you probably well know, doing astronomy just after the Sun has disappeared below the horizon is tough, especially if you intend to look in that general direction. At 8:30pm EDT, Mercury will be just about 10° above the horizon and visible in the twilight glow. As far as planets go, little Mercury is the runt of the inner Solar System, the first of the so-called "Terrestrial Planets" (as opposed to the outer Solar System, which is dominated by the "Gas Giants"). It isn't big at all, a little over 3000 miles (4880 km) in diameter, about 1 1/2 times the size of our own Moon. Because of that, don't expect much even with a big telescope; Mercury is a small planet to begin with, and we're seeing it from over 100 million miles (160 million kilometers) away. The problem locally will be one of haze. We're entering into the hot months now, and northeast Florida does get notoriously hazy this time of year. However, we're also expecting storms on Friday, and they can help to clear a lot of that up. Either way, little starlike Mercury is only the beginning of the happenings on the 16th. A better show is just a little higher up.
From time to time, the planets appear to close in on one another in our skies. Of course, they are actually very, very far apart, but this does make for some great observing possibilities. That's what we'll have in Saturn and Mars.

(image courtesy of "Solar System Live" )

They're going to look close. Real close. The apparent angle of separation (that's geek-speak for how far they appear apart) will be around 1°, or almost two full Moons. Due to the enormous differences in their sizes, though, they will look very different from one another. Mars is a little more than half the size of Earth, 4221 miles (6794 km) and glows with an orange-tan glow. Saturn, on the other hand, is over 17 times as big, almost 75000 miles (120700 km) in diameter. Even though Saturn will almost be a billion miles out (1.6 billion km), it will still outshine Mars!
The Vagabond Astronomer will be setting up at County Dock in Mandarin around 8:00 pm. This gives us the best view west. Because of how crowded the conditions are out there, only one scope will be used, and no, I will not be setting up on the dock itself but next to it. Besides, brackish water and fine optics do not a good couple make.
Hope to see you there.

Wednesday, June 07, 2006

Practicing Random Acts Of Astronomy

Why be random?
The late spring months here in the northern hemisphere seem ideal for astronomy, at least for the climate. True, the deep sky really isn't that interesting until summer rolls on in. Fortunately, right now we're blessed with Saturn still visible in the west, Jupiter brilliantly glowing in the east, and for the last two nights, a nice first quarter and waxing gibbous Moon. The nice thing about these objects is that light pollution doesn't really make an impact on them.
Which brings me back to the whole random issue.
At all times, yours truly keeps two telescopes on alert standby; my little 55mm copyscope refractor "Lil' Bernie" and my 152mm (6") Schmitt-Cassegrain "Dyna". Most of the time, they simply live in my car (which, I'll have you know, is a 1986 model Chevrolet Celebrity that sounds and feels like it's trying to break the sound barrier when passing 55 MPH). The nice thing about this arrangement is that it allows me to just setup a telescope anywhere, at any time. There's also a box of eyepieces, and occasionally Lil' Bernie's solar filter.
This means that sometimes I'll post a session here in the VA Blog after the fact. Like now. In fact, not just one session, but two. Done on the spur of a moment. Randomly. Spontaneously (note the use of single words for emphasis. And fragments. Great literary device. Must use this again. Later).
Last night, 6th June, 2006, I setup in the field at Mandarin Park before sunset. Seems a little odd, but the Moon looked perfect against a sapphire backdrop. This was a great opportunity to introduce park visitors to our nearest celestial neighbor, and indeed a few people did partake of this little slice of the sky. It is amazing what can be seen on the Moon even with the Sun still high in the west. That session ended before 9 PM, and was pretty straightforward.
Tonight, though, I did something I've been wanting to do for years. I sat up Dyna and Lil' Bernie on the sidewalk outside of Fort Castillo de San Marco in beautiful St. Augustine, near the water's edge. This was a great location to take in not only the Moon, but because it was later, we were able to catch Jupiter as well. Sadly, Saturn was simply too dim, occluded by thick cirrus clouds, looking like dark mare's tails against a darkening sky.
The biggest problem was one of parking. I had to park over a quarter of a mile (500 meters, give or take) from where I wanted to setup and lug the equipment. I'm not as young as I used to be, but miraculously, I survived.
Most of the people who came up (all in all, I reckon 30 in total) were tourists, save for one mature couple who just moved to St. Augustine from Ft. Lauderdale. In fact, they sat on the sea wall nearby and pretty much kept me company most of my session. The children tonight really made it all worthwhile. They'd look at the Moon and Jupiter, mouths agape with "whoa"'s and "wow"'s.
By 9:30 PM, I decided to call it a night. I was tired and dreaded carrying almost 100 pounds (for you metric folks... around 50 kg) back to my car. The trip home, my car vibrating and rattling as I tore through the night down Interstate 95, sounding at times like it was trying to survive atmospheric entry, I reflected on it all; the
gibbous Moon hanging there over Anastasia Island, the thin, wispy clouds still catching the vanishing rays of the Sun, Jupiter shining like a mad diamond, the smell of saltwater and the feel of a stiff ocean breeze. And the people who came up and wanted to catch their own little piece of the sky.
That's what practicing random acts of astronomy is all about.