Tag: space

Voyager

Voyager approaching the heliopause (from NASA).

The Voyager spacecraft, launched in 1977, are still going and making new discoveries. They are after all the man-made objects that are furthest away from the center of the solar system, beyond the orbit of Pluto, and are now approaching interstellar space.

Where does the solar system end and interstellar space begin? Well, the Sun gives off light, but it also emits a plasma of charged particles (protons and electrons typically) that’s called the solar wind. These charged particles are launched from the Sun pretty fast, but as they get to the edge of the solar system they start to slow down, because the solar system is moving through a magnetic cloud, and, as we all know, charged particles are affected by magnetic fields.

The solar wind, assisted by the Sun’s magnetic field, pushes against the interstellar magnetic cloud, creating a bubble, called the heliosphere (helio=sun, sphere=sphere) that is pretty much the edge of the solar system.

Both Voyager spacecraft are approaching the heliosphere, and we’ve recently discovered that as the solar system moves through the interstellar magnetic cloud, the heliosphere is pushing against the cloud and the cloud is pushing back quite a bit. As a result, the heliosphere is shaped like the bow wave of water around a speeding boat.

It is difficult not to personify these two lonely spacecraft as the get further and further away from home, with no way to get back, but sending signals that tell of their discoveries and ensure their immortality.

The Galilean moons of Jupiter

Io over Jupiter taken by NASA's Cassini spacecraft.

400 years ago, on January 7th, Galileo Galilei made his first observations of Jupiter. You can see his notes below. The big circle is Jupiter and the small dots are the specks of light he observed adjacent to the planet. Later observations showed that the specks did not stay in the same place, and lead him to realize that he was seeing moons orbiting the planet.

Galileo's notes from Jan 7, 1610.
Translation of Galileo's notes (from NASA).

Galileo used a 33x telescope, which is pretty weak by modern standards, in fact you should be able to see Jupiter and it’s moons with a good pair of binoculars. Since the Catholic church at the time preferred the view that the Earth was the center of the universe, when Galileo published his observation he got into a bit of trouble. In his publication Galileo wrote:

On the 7th day of January in the present year, 1610, in the first hour of the following night, when I was viewing the constellations of the heavons through a telescope, the planet Jupiter presented itself to my view, and as I had prepared for myself a very excellent instrument, I noticed a circumstance which I had never been able to notice before, namely that three little stars, small but very bright, were near the planet; and although I believed them to belong to a number of the fixed stars, yet they made me somewhat wonder, because they seemed to be arranged exactly in a straight line, parallel to the ecliptic, and to be brighter than the rest of the stars, equal to them in magnitude . . .When on January 8th, led by some fatality, I turned again to look at the same part of the heavens, I found a very different state of things, for there were three little stars all west of Jupiter, and nearer together than on the previous night.

The above quote comes NASA’s page on the discovery of the Galilean satellites (for a full translation of the entire document go to: The Starry Messenger). The NASA page also has another neat quote, from Simon Marius describing how the moons got their names:

Jupiter is much blamed by the poets on account of his irregular loves. Three maidens are especially mentioned as having been clandestinely courted by Jupiter with success. Io, daughter of the River, Inachus, Callisto of Lycaon, Europa of Agenor. Then there was Ganymede, the handsome son of King Tros, whom Jupiter, having taken the form of an eagle, transported to heaven on his back …

For perspective, the image below, of Io’s surface, was taken by NASA’s Galileo spacecraft. Click on the image to get to the high resolution version.

Closeup of Io
Closeup of Io's surface.

The Galileo Mission website is a great resource about the mission to Jupiter and about Galileo Galilei himself. You can also find out what NASA’s up to with respect to Jupiter here.

Geometry and the height of the mountains on the moon

Galileo's image of the moon
Galileo's map of the moon.

Galileo Galilei matched careful observation of sunlight and shadows on the moon, with some beautiful geometry to estimate the height of lunar mountains, in 1609. He needed the Pythagoras’ Theorem and the quadratic formula, both of which middle school students should be familiar. Larry Phillips has a nice post describing how Galileo did the math. The image below (from Pioneers of Science shows how to get started.

From the Gutenberg Project eBook of Pioneers of Science by Oliver Lodge.

The Moon transits the Earth

(from NASA).

Perhaps one of the most amazing sequences of images ever taken. NASA’s Deep Impact spacecraft took these movies looking back at the Earth from 50 million km away. You can see the moon clearly crossing the face of the planet. This really resets your perspective. The full movie is below.

How to fly through space

Interplanetary spacecraft
Ion thruster spacecraft. Image from NASA.

To get anywhere in the solar system takes a long time and is not easy. The Mars rovers took years to get there and were built to be very light because heavier spacecraft are harder to lift into orbit and take more energy to get them where they’re going (and to slow the down when they get there). Getting humans to other planets, or even another solar system, is an even greater challenge. New Scientist magazine has a nice little article on different types of deep-space spacecraft that might work.

Clouds on Mars

Clouds on Mars seen from the Mars Pathfinder

Discover Magazine blogger Phil Plait has a great post showing clouds formed by air rising over the volcanic mountains on Mars (orographic clouds). The simple animation is fascinating to see, but what’s even more interesting is how they were made. The images were taken by Emil Kraaikamp who uses a telescope in what appears to be his backyard. Each image in the series that makes up the animation is a composite from images taken with red, blue and green filters. Plait has a very good explanation of the process:

I love this, because it shows how using filters tells you a lot about what you’re seeing. Note that in the red Mars is fairly smooth, with some dark spots. The red dust covers the planet, so it smooths out features (though the ice caps are obvious). In the green you’re just starting to see a hint of clouds, and then in the blue the clouds pop right out.

Combine them, and you have Mars. Another world, seen through what most people would consider a small telescope here on Earth.

Photography is a wonderful medium for combining science and art as you manage the exposure to create interesting effects. If you understand a little about how cameras work, the page on the equipment used to take the pictures is quite fascinating.