Posts Tagged ‘planets’

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.


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 to see an overview of stargazing opportunities in November.