April 29, 2010

Katelyn Allers, assistant professor of physics and astronomy.

(Editor's note: "Ask the Experts" will resume weekly publication in the fall. Until then, please enjoy this edition originally posted this past spring.)

LEWISBURG, Pa. — Welcome again to "Ask the Experts," a regular web feature that highlights the expertise of various Bucknellians in a range of topics related to current news events and other timely subjects. || Ask the Experts archive

This week, we asked Katelyn Allers, assistant professor of physics and astronomy, about the best viewing in the summer night sky and brown dwarfs — space objects that are neither stars nor planets but help us better understand both.

Q: With the summer coming up, what kinds of things should amateur astronomers be looking for in the night sky? Where and when is the best place to view the summer sky?

A: To get into astronomy, you don't need a telescope. There's a lot that you can see and have a great time exploring the night sky with just a pair of good binoculars. Just find a dark place and either lie down or use a tripod to keep your binoculars steady.

If you've never looked at the moon through a pair of binoculars, it's breathtaking. You can see maria (large, low-lying dark areas) and craters, most of which were created almost 4 billion years ago.

Planets are also wonderful to look at with binoculars. Saturn is currently visible, as are Venus and Mars in the west around sunset. With Venus you can see its phase with binoculars (similar to the phases of moon). Galileo observed the phases of Venus, and it provided early evidence that the sun, and not the earth, was at the center of our solar system.

There are some other interesting things to look at during the summer. The Andromeda galaxy is a great place to look if you're somewhere with dark skies. There are some globular clusters, M22 and M13, which you can easily see with binoculars. Double stars are also great for amateur observers. One of my favorites is Alberio, which we have dubbed the Bucknell star because one of the stars is orange and the other is blue.

If you want to start exploring the night sky, the first thing you should get is a star chart. They're inexpensive, or you can find them online (check out skyandtelescope.com) and print them out. Identifying constellations can be a fun activity, and the star chart also provides a road map for finding and exploring many astronomical objects.

Even if you don't have access to a telescope or binoculars, there are wonderful things to observe with the "naked" eye. The Perseid meteor shower in August is fantastic. The rate of meteors peaks Aug. 12 with almost 80 meteors per hour. The best time to go out and observe a meteor shower is after midnight and before sunrise. Meteor showers occur when the earth's orbit crosses the debris field left behind by a comet. In the case of the Perseid meteor shower, you're seeing ancient debris from comet Swift-Tuttle burn up in our atmosphere.

Q: Your research deals mainly with brown dwarfs, objects bigger than a planet but smaller than a star. What does this research mean to the average person?

A: A brown dwarf is less than about 72 times the mass of Jupiter so, like Jupiter, it doesn't have enough mass to sustain hydrogen fusion. Yet, a brown dwarf doesn't have a parent star, so it hasn't formed in the disk of a star like the planets in our solar system did. This is precisely the reason we want to study them; they're in a mass and temperature range that bridges the gap between stars and planets.

The lowest-mass brown dwarfs are very good analogues for extra-solar planets. In 2008, astronomers directly imaged extrasolar planets, meaning that we actually saw the light coming from the planet itself - not the doppler wobble of its host star, nor a light dip as it goes in front of the star. Ideally, we'd like to get spectroscopy of these planets to infer their masses, temperatures and compositions. Here we run into a problem because trying to get spectroscopy of these planets when you have a whopping bright host star nearby is really difficult.

This is where brown dwarfs save the day, as they provide an observational template for what we expect these planets to look like, so we can infer the properties of the planet based on what we know about brown dwarfs.

For stars, many questions remain about the way that they form. We know that you have gas and dust out in space. That gas and dust forms giant molecular clouds, which eventually form clumps with enough mass and gravity that they're able to overcome gas pressure, collapse and form a star.

One way to test the fine details of the model for star formation is looking at the extreme ends. Looking at brown dwarfs which have very low mass and seeing how efficiently they're formed tells you about the process of star formation itself.

We're looking at things that have very low masses; how they managed to overcome gas pressure with these small masses and even become brown dwarfs is a compelling question.

Q: Your research has taken place in observatories in Chile and Hawai'i. How does being in Pennsylvania affect your research? Are there things you can see here that you can't see there, and vice-versa?

A: The telescopes we have here at Bucknell are fantastic, but brown dwarfs are intrinsically very faint objects, so they require observations with large diameter telescopes. In addition, many of the objects I study have southern declinations, and simply aren't visible at our northern latitude.

Being in Pennsylvania, however, hasn't affected my research at all. A lot of telescopes allow you to observe remotely (through computers). I've observed on telescopes in Hawai'i multiple times over this past school year. You're on the phone with an operator in Hawai'i and you can run the instrument and obtain your data without having to physically be at the observatory. Though a trip to Hawai'i in the dead of winter might have been nice!

Q: You've talked of taking students to large observatories in Hawaii and Chile. What would you hope they would gain from such a trip?

A: I just got back from a trip to Chile, with Abby Peltier, a Bucknell physics junior. We got some great data to look for brown dwarfs in the Ophiuchus region.

We were observing on a four-meter class telescope in the Andes Mountains. The stars that are visible change over the course of a year, so April was a good time for observing Ophiuchus, the region we were targeting.

The experience was a good one for Abby; just learning how to plan observations and take data is a great thing for students to learn. There's a wow factor, too, when you're observing on a large telescope in such a beautiful location.

For professional astronomers, being awarded time on large telescopes requires a successful peer-reviewed proposal. It's nice to have a merit-based check that lets you know your proposal is sound - that it's worth spending telescope and personal resources to pursue.


New editions of "Ask the Experts" will appear on the Bucknell website on most Thursdays during the fall and spring semesters and on occasion throughout the summer. If you have ideas for future questions or are a faculty or staff member who would like to participate, please contact Sam Alcorn.

To learn more about faculty and staff experts who can speak on a variety of news topics, visit Bucknell's searchable Experts Guide.

Contact: Division of Communications

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