Speaking of Hubble...

Archive: Tracy Vogel

Pluto in Hiding

September 28, 2012 by Tracy Vogel
No, Pluto is not ready for its close up, thank you.

No, Pluto is not ready for its close up, thank you.

Oh, Pluto. Beloved Pluto. The endearing, scrappy runt of our solar system litter, demoted but never defeated. We heart you, you crazy little Kuiper Belt Object, with your icy surface and newfound moons and multiple references to Disney films, what with Mickey Mouse’s dog and now the dwarf planet thing. Hi-ho, Pluto. Hi-ho.

So today we’re going to discuss a question I encounter on occasion. “Hey,” it goes, roughly, “How come we can see all this detail in a galaxy 46 million light-years away, but your pictures of Pluto look like someone airbrushed a basketball and photographed it through a Vaseline lens at the bottom of a swimming pool? Pluto’s right next door, while this galaxy is clearly at least as far away as the mall.”

Well, aggrieved person suspiciously intent on invading Pluto’s privacy, first understand that these images are actually really neat. This is the most detailed view ever of the entire surface of Pluto. You’re watching the seasons occur on an object so far away that it takes light from the Sun over five hours to reach it. We’re honestly a little hurt. Do you know how much effort that took? How much manpower? Do you think it’s easy to smear that much Vaseline on a lens in space? It is not.

You are right, though – Hubble’s pictures of Pluto do lack the detail people have come to expect from the telescope. Basically, it’s an issue of size. To understand it, you have to understand something called “angular resolution,” which – where are you going? Get back here right now, Pluto e-mailer, and listen while I explain angular resolution to you in excruciating detail! That’s right. We’re all in this together, now.

So, angular resolution. Draw two lines on a piece of paper and have a friend hold that paper up and start to walk backwards. Eventually, you’ll only see one line. That’s angular resolution in action – the ability of a picture-taking device – in this case, your eye – to distinguish between details. If you use a much bigger piece of paper, and draw the lines farther apart, your friend will get farther before you stop seeing two distinct lines. Both size and distance matter when it comes to angular resolution.

Angular resolution is a set thing – for eyes, for cameras, and for telescopes. The human eye has an angular resolution of about one arcminute. Hubble has an angular resolution of .05 arcseconds. That’s good enough to stand on the East Coast of the US and distinguish between lines spaced about three feet apart on a piece of paper that your friend is holding up on the West Coast. Also, that’s one really good friend you have there. Does he owe you money, or a kidney, or something?

Now, galaxies are huge. When Hubble looks at a galaxy, it’s observing a collection of immense objects at incredible distances from one another. (Even then, you’re usually seeing clusters of stars, not individual stars in these galaxies – Andromeda is about the farthest galaxy in which Hubble can actually resolve individual stars.) The beautiful spiral galaxy NGC 2841 is a bit over two arcminutes in size.

Little Pluto? He’s about .06 to one arcseconds wide in the sky.

The angular resolution of a telescope, just like the angular resolution of your eyes, is fixed. Hubble is resolving both the galaxy and Pluto the exact same way. But one has a lot more space and size to work with than the other.

These images of Pluto are painstakingly compiled from lots of Hubble data with the help of years of computer processing. As one astronomer put it, they’re really maps, not pictures.

But it’s not over, saddened, would-be Pluto observer. You’ve got 2015 to look forward to, when the New Horizons spacecraft will complete its decade-long, 3-billion-mile journey to the smallest sort-of member of the solar system and give us a spectacular, up-close view of this Kuiper Belt object … for six months. And then it’s back to fuzzy basketballs as seen through multiple layers of gauze on a foggy day with debilitating nearsightedness.

So time will be, as they say, of the essence. And that’s when those seemingly dull Hubble maps will prove their worth, helping astronomers decide the most interesting areas on Pluto for the probe to target while it can.

Telescopes as Time Machines

August 31, 2012 by Tracy Vogel
Credit: T. Rector and B. Wolpa (NOAO/AURA/NSF)

The light from our neighbor Andromeda is 2.5 million years old. CREDIT: T. Rector and B. Wolpa (NOAO/AURA/NSF)

Hi everyone. My name is Tracy Vogel, and I’m a writer and editor for the Office of Public Outreach at the Space Telescope Science Institute. I’m also the person who answers e-mail for HubbleSite. You know how you shoot off an e-mail to HubbleSite and expect it to get answered by some kind of automated robot? That’s me! I’m the robot! Hi! It’s very exciting to meet you all, and to finally be able to point out that Hubble, a non-sentient telescope floating through space, neither needs nor possesses a LinkedIn account. Though I’m sure it would thank you all for the many, many, many gracious invitations.

Unlike the other members of this blog, I’m not an astronomer. But I do spend a lot of time asking them questions. “Can Hubble be seen with the naked eye?” “Do we know the age of the universe?” “Are we scheduled to observe that giant invisible death planet that’s going to crash into the Moon?” (The answers are, respectively: “Yes,” “13.7 billion years,” and “Can I see your employee ID, again?”)

Why do I need to know these things? Well, it’s probably my unquenchable thirst for knowledge. Or my massive, overflowing inbox of e-mail queries. One of those! And since the questions we get are actually quite interesting, and at least a handful are not written in all-caps by people who appear to be typing by gnawing on the keyboard, we thought we’d share them with you. To elucidate you, the public, with your inquisitive minds and your curiosity-driven missives and your obvious homework questions that you’re clearly hoping I will do for you so you can get back to playing Mario Kart. (Yes, of course all the answers are “The Crab Nebula,” hopefulsixthgrader@gmail.com! You can trust me! I work for science.)

Anyway! Occasionally I’ll be jumping in on this blog to discuss some of our more common or uncommon questions, or Hubble news of note. Because they are paying me, and our public demands it. In between bouts of Mario Kart.

Today’s question is one we get fairly often: You keep talking about seeing galaxies in the past. How does that work, anyway? The past is, well, past — thus the name. How does having a telescope let you see something that happened millions of years ago?

To understand this, you first need to know something about how a telescope works. Telescopes provide you with a bigger lens than the ones you have in your eyes. Because it’s bigger, it can capture more and much fainter light than your eyes can on their own. But telescopes don’t reach out into space — they stay right here (or 353 miles above here, in Hubble’s case) and wait for the light to hit.

Light moves. It moves extremely fast — at about 186,000 miles per second — so it looks instantaneous when you flip a switch, but it takes time to travel across the vast distances of space. Light from the Moon takes about 1.3 seconds to get to Earth, so when you look up at the sky, you see the Moon as it was over a second ago. Light from the Sun takes 500 seconds to reach us; the sunlight hitting your face is over eight minutes old.

Other galaxies are so far away that we actually measure the distance to them in the time it takes light from them to reach us — the “light-year.”

The nearest large galaxy, Andromeda, is 2.5 million light-years away, thus its light takes 2.5 million years to reach us. When you look at Andromeda, you’re seeing ancient history. And if you lived in the Andromeda galaxy, and you were looking at the Milky Way right now, you’d be seeing this galaxy as it was 2.5 million years ago. Wave hello to Earth’s Glyptodonts, Andromedeans! They won’t wave back, as they’re deeply, extremely, enthusiastically extinct, but that’s no reason to be rude. Upon further reflection, it seems like a good reason to be extra polite. A moment of respectful silence, everyone, for the Glyptodonts. I think we can all agree that the world would be a better place today if it still had Volkswagen-sized armadillos. Thank you.

Anyway. The point is that the farther away an object is the longer it takes for the light to reach us. So the light from the most distant objects we can see started traveling billions of years ago, when the universe itself was young.

So that’s why Hubble can look at deep space and see objects as they were far in the past. Doesn’t seem quite so odd when you realize you’re doing it yourself, every time you look at the stars, does it?