Archive for the ‘Stargazing’ Category

Question: Why do stars twinkle?

November 9, 2007

On Nov. 3 a fellow stargazer posted a question for astronomy graduate student Matt Davis on the Interview with Matt Davis page of this blog.  The question:  Why do stars twinkle?  I e-mailed Davis the next day about the inquiry, as promised.   (Thanks, Jay!)

The answer:  “Stars twinkle because we are looking at them through a thick, constantly moving layer of air:  Earth’s atmosphere,” Davis said.

Davis gave a great analogy of the twinkle-star effect:  “Imagine you are out in the desert on a hot day, looking down a straight road,” he said.  “As you look down the road, the line on the road seems to shift around and the air looks like it’s shimmering and moving.  This is because the air next to the road is very hot and it’s rising, as hot air does.  This means that the air is changing density and moving along your line of sight, and this causes things you see through that air [to] appear to move and shimmer.”

“This is the same effect we see as we look at stars or the distant lights of a city,” Davis said.  “All of the air between you and a star or [the] light is moving around.   Different parts of [the air] have different temperatures and different densities so it bends the light around, making it look like it’s twinkling.”

The twinkle-star effect is the main reason astronomers put telescopes (like the Hubble Space Telescope) in orbit around Earth, he said.  Above the atmosphere “the stars … no longer twinkle and we can take much clearer pictures,” Davis said.

“Interestingly, planets do not appear to twinkle the way stars do because they have an actual finite size because they are so much closer to us than the stars,” he added.  “If you look at a planet through binoculars you will see that it has a disk, [whereas] stars still just look like points.  This makes it so that the light from a planet gets kind of averaged out so that we don’t see it twinkle.”

For another good answer to why stars twinkle, read what volunteers in the Astronomy Department of Cornell University had to say on the Ask an Astronomer Web site.

Again, please post any questions about stargazing to this blog.  I’m happy to work as an intermediary for other interested stargazers.  Davis, a self-proclaimed “extragalactic distances guy,” encourages inquiries about celestial phenomena outside of the Milky Way galaxy.

Oh, and check out StarDate Online’s seven-day star forecast for the nights Nov. 8 to Nov. 14.

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Stargazer Top Five: A list of stargazing must-sees

November 5, 2007

In my interview with astronomy graduate student Matt Davis on Oct. 16, I asked him to suggest his favorite stars and constellations for amateur stargazers to look for in the night sky.  Davis responded by giving me a list of celestial phenomena he thinks stargazers shouldn’t miss.  Below is the Stargazer Top Five, a list of stargazing must-sees, devised from his suggestions:

1.  The Milky Way galaxy.  “If I had to make a list of all the things [stargazers] should see, the Milky Way tops the list,”  Davis said. 

I knew the Milky Way is the galaxy of our solar system, but I wanted to know:  Why does the Milky Way look the way it does from Earth?  The Milky Way is a combination of billions of stars and dust, Davis said.  “The Milky Way is a fuzzy glow of so many stars shining at us that we can’t distinguish any of the stars,” he said.  “It’s combined light from all of the stars of the Milky Way that we can’t see individually.  We are orbiting perpendicular to the galaxy, so that’s why we kind of see it overhead.  And you can’t tell, but the center of our galaxy is in the constellation Sagittarius.  When you’re looking at the constellation Sagittarius, you’re looking at the direction of the center of our galaxy.”

2.  The planets.  “It’s always cool to identify the planets,” Davis said.  According to StarDate Online, the planets Mercury, Venus, Mars, Jupiter and Saturn are visible to the naked eye.  For information on when and where to view the planets, see StarDate Online’s planet viewing guide.

3.  The Pleiades star cluster.  What’s most interesting about the Pleiades star cluster– or any star cluster– is that unlike the stars in a constellation, “those stars are actually physically associated with each other,” he said.  “It’s a cluster of young, bright stars born at the same time, in the same location.”  Stargazers can find Pleiades in the Taurus constellation.

4.  The star Sirius.  Sirius should be easy to spot because it is the brightest star in the sky, Davis said.  “Because Sirius is so bright, the light sensitivity of your eye will actually try to determine the color of the star,” he said.  “It’s very pretty.”  To learn more about Sirius, see StarDate Online’s radio program transcript of a discussion on the star.  Stargazers can find Sirius in the Canis Major constellation.

5.  The Delphinus constellation.  Davis said Delphinus is the best constellation in the sky.  “It’s cute– it’s a dolphin,” he said.  But to him, Delphinus looks more like a kite.  (Funny thing:  My friends and I have spotted the ‘kite’ numerous times while stargazing, not knowing it was an actual constellation.)  Using my star map, I figured out that Delphinus lies near the celestial equator, just east of the Milky Way.  It is surrounded by the Pegasus, Equuleus, Aquila, Vulpecula and Sagitta constellations.

Remember to check StarDate Online’s seven-day star forecast for the nights Nov. 4 to Nov. 10.  Fellow stargazers may also want to go to stardate.org to see an overview of stargazing opportunities in November.

Stargazing tips: Make the most of a starry night

October 18, 2007

Last week I posted a blog listing a number of stargazing necessities.  This week I’ll be going over some stargazing tips.   Or, more specifically, ways to make the most of a starry night.

On Oct. 16, I talked to astronomy graduate student Matt Davis, and he gave me a list of suggestions for the amateur stargazer.

Davis said it’s important for a stargazer using a star map or a star chart to determine which way is north and to get oriented with the night sky.  “The best way to do that is to find Polaris, the North Star,” Davis said.  He said the easiest way to find the North Star is to first find the Big Dipper– which isn’t really a constellation but an asterism* that is part of the constellation Ursa Major— and draw an imaginary line from the two stars that make up the edge of its bowl, called the pointers, because they roughly point to the North Star.  (An added bonus:  The North Star is the tip of the handle to another asterism called the Little Dipper, part of the constellation Ursa Minor.)

Not only does the Big Dipper make spotting the North Star easier, it also acts as a signpost to other asterisms and stars.  Pathways to Astronomy says to try this:  Visually extend the arc formed by the stars of the handle of the Big Dipper and find the orange star Arcturus in the constellation Bootes.  I’ll definitely be looking for Bootes the next time I go stargazing.

Davis also suggests stargazers use their hand to measure distances and get a better idea of the location of stars and constellations.  “The sky is broken up into degrees, so if you want to measure how many degrees something is from the horizon you can either use a fancy instrument or you can use your fists,” Davis said.  “There are a bunch of different tools you can use:  your hand spread at arm’s length covers an angular size of about 20 degrees, your fist is about 10 degrees, your thumbnail is about two degrees and your pinky fingernail is about one degree.”  (For more information about locating stars and constellations, see StarDate Online’s cooresponding FAQ answer.)

Stargazers can also use the hand-measuring method to find their latitude, he added.  “If you want to know your latitude, go outside, find the North Star and find a way to measure how far the North Star is away from the horizon– [that’s] your latitude.  Just start stacking fists.”

Should stargazers have any difficulties seeing a faint star, Davis advises them to use their peripheral vision to look at the star instead of looking directly at it.  “When you look straight at something you’re using the color-sensitive parts of your eye,” he said.  “At night you start to lose the ability to see colors.  At night everything looks gray, so we sort of switch to using the light-sensitive parts of our eyes.  Your peripheral vision is most sensitive to light and dark.”  I had a friend tell me about this little trick, too.  Looking off to the side really does help.

Don’t forget to check out StarDate Online’s seven-day star forecast covering the nights from Oct. 18 to Oct. 24.

*Pathways to Astronomy defines an ‘asterism’ as “an easily identified grouping of stars, sometimes a part of a larger constellation (such as the Big Dipper) or extending across several constellations (such as the Summer Triangle).”  Asterisms are not included in the 88 constellations officially recognized by astronomers.

Stargazer necessities: More than just a pair of eyes

October 12, 2007

I’ve scoured the Internet for websites that offer weekly stargazing tips, and my favorite by far is StarDate Online, provided by the University of Texas McDonald Observatory.  Stargazers may choose to subscribe to a monthly newsletter and receive e-mails about stargazing opportunities.  Of course, I will create a link in my blog posts to their seven-day star forecast, the first of which covers the nights from Oct. 11 to Oct. 17.  (Or try http://spaceweather.com.)

But before any beginning stargazer clicks on that link, I need to go over a few things.  Namely, what a stargazer needs to observe the night sky.  I already knew I needed more than just a pair of eyes, but I wanted some advice as to what that entails.

On Oct. 8, I talked to Dr. Ana Larson, a senior lecturer of astronomy, about stargazing necessities and asked her for a few recommendations.  She told me the most important thing beginning stargazers need is “a desire to look at and learn about the stars.”

To get the most out of their stargazing experience, stargazers need “wonderment, desire to learn more about what they’re looking at– an interest to find out what’s all out there instead of just white twinkly things,” Larson said.  “They’ve got to ask themselves questions:  Why are some stars brighter?  Why are some stars different colors?  Why do stars die out?  Why are they born?” 

Okay, stargazers need to be curious about the night sky.  I know I am.  What else do stargazers need?

Larson recommends stargazers get a star map or a star finder.  I downloaded a great star map from www.skymaps.com for Oct. 2007.  “Take it with [you] at night, and then dial up what to look for in the sky,” Larson said.

Which means stargazers will also need to bring a flashlight.  However, the flashlight should be dim or red.  Bright, white light will ruin the eyes’ sensitivity to light and make it harder to see stars.  StarDate Online suggests taping red cellophane over a flashlight.  Okay, I can do that.

Stargazers will also need to go to a place that is dark and has a clear view of the night sky, away from city lights.  She said the closest, easiest and darkest place she can think of is Rattlesnake Lake, just south of North Bend.  (I couldn’t believe she’d mentioned Rattlesnake Lake, because I love to hike up Rattlesnake Ridge!)  She said the view from the parking lot works fine.  (For more help finding a good stargazing site, see StarDate Online’s corresponding FAQ answer.)

Larson also recommends bringing a pair of binoculars, for when stargazers wish to see farther than the naked eye.  “A high-power [pair of binoculars] is not needed,” Larson said.  Good.  I’ve got a pair of those.

A quick run-down:  I’m a curious, amateur stargazer equipped with a star map, dim flashlight, a dark destination and binoculars.  (For a more in-depth list of necessary equipment for stargazing, see StarDate Online’s suggestions.)  But even with all of these things, I asked, how should I go about stargazing? 

Larson replied, “Actually, what I do is what so many astronomers do:  I just look up and see what’s around.  It’s comforting to me to know that the stars are still out there.  I can always just look up at the stars.”