Stargazing on Vacation

I just took a few days off from cyberspace, recharging my batteries for writing. It helps a lot to step away from the keyboard and do other things—like watching sunsets. We’ve been doing it every clear night this summer. Each one is amazing, even when there are a lot of clouds in the sky. We get really dramatic sunsets, like this one.

Lately, just after sunset, the planet Venus has been putting on a show in the western twilight. You can’t miss it. It’s the bright dot of light that isn’t quite like a star. It’s going to be visible for another few weeks, so check it out.

If you wait a bit longer, you can spot Saturn in the southwestern sky. That one’s worth looking at through a small telescope if you have one handy; it’ll help you see the rings of Saturn.

After that, you just have to wait for the stars to come out.  When it’s dark enough, you can start to make out some familiar constellations.  And, if it’s really dark, you might be able to spot the Milky Way stretching across the sky.

Many stargazers use starcharts to find their way around. Many smartphone apps, such as Starmap (for iPhone) and Mobile Observatory for Android, can help you learn the constellations.  You can also download Stellarium (a free desktop planetarium program). There are many others available, so just do a search for stargazing software in your browser.

While you’re stargazing, you might see some bright flashes across the sky. In August, it usually means you’re seeing Perseid meteoroids. These are bits of space debris about the size of dust specks or grains of sand. They crash through our atmosphere and vaporize on the way in. The streak you see is a meteor. If a piece of this space stuff hits the ground, it’s then called a meteorite. Perseid meteors are bits of debris left behind by the comet Swift-Tuttle as it makes its way through its orbit. Earth’s orbit happens to pass through that cloud of dust grains in August each year. The meteors appear to come from the direction in the sky of the constellation Perseus. The shower peaks early on the morning of August 12th, but you can see its meteors for the next couple of weeks.

I always associate stargazing with summer nights for some reason. Of course, you can do it year-round, as long as you dress warmly for those winter stargazing nights. But, I guess it’s because my earliest memory of stargazing was on a warm spring night, and I just continued during the following summer. It’s a great time to start skygazing, and introduce kids to it, too!

Mysteries Hidden in a Few Pixels

Last week many (if not all) folks on planet Earth had the chance to glance up at the skies and wave at a distant planet. Around each of the two worlds–Saturn and Mercury–are circling spacecraft with cameras powerful enough to look across the solar system and take images of our planet and its moon. We saw the images from Saturn last week (and if you didn’t, check them out at the Cassini page).  A couple of days ago the team working with the MESSENGER mission at Mercury released their spacecraft’s view of our planet. Not surprisingly, our planet looks like a tiny outpost set against a backdrop of stars.

MESSENGER took this image while it was searching out any natural satellites that might be orbiting Mercury. As far as we know, Mercury doesn’t have any moons or we would have spotted them by now.  However, it might have some very small satellites that haven’t yet been spotted; they would be only a few kilometers across at most. It just so happened that Earth and the Moon would be photobombing during one visual sweep, so astronomers announced the time and date for everybody to smile and wave at Mercury.

As you can see from this distance, our home world is pretty small. The moon is a blip next to it. Yet, MESSENGER’s camera caught the pair largely because they were looking for dim objects and the Earth/Moon combo appear very bright by comparison to small rocky moonlets.

The Earth and Moon appear very large in this picture because they are overexposed. When looking for potentially dim satellites, long exposures are used to capture as much light as possible. Consequently, bright objects become saturated and appear artificially large. In this image, Earth and the Moon are each less than a pixel in size. At that tiny scale, it’s impossible to make out any details on the surface of either world.

(The “tails” pointing downward from the Earth and Moon are artifacts caused by the image saturation. These can be seen clearly in the zoomed image in the center lower panel. Anyone who has ever aimed a digital camera at a bright object has likely seen these “blooms” that happen when cameras are overburdened with light.)

MESSENGER took more than one image of the Earth-Moon system. On July 20th it caught our two worlds in the spotlight again, this time on the 44th anniversary of the Apollo 11 landing on the Moon. If you could see the landing sites at 1-pixel resolution, they would appear as they do in the image on the lower right.

There’s SO much hidden in a few pixels of a distant world. As we look out at other stars with planets, it’s important to know that they, too, hide some incredibly cool things to discover. So far, Earth is the only planet we KNOW harbors life, and it’s not even evident in this image. Makes me wonder just what we’ll find when we figure out ways to explore worlds around other stars!