September 14th: Measuring the Stars' Light

Date: September 14, 2011

Title: Measuring the Stars’ Light

Podcasters: Thomas Hofstätter and Leon Dombroski

Organization: :: The Hidden Space Project ::

Links: http://hidden-space.at.tf

Description: What are some of the brightest stars in the sky? Astronomers use a special term to talk about the brightness of stars: magnitude.

If you have any questions, comments or suggestions to the podcast, feel free to write me an email to hidden-space (at) gmx (dot) at or visit me at my website at www.hidden-space.at.tf!

Bios: Born in 1993 near Vienna, Austria, Europe. Upper High School with focus on Computer Science. Interested in extreme small and extreme big, devious and uninvestigated things. My main aim is to bring astronomy to public and to establish secular interest in astronomy, physics and mathematics. Host of :: The Hidden Space Project :: at http://hidden-space.at.tf.

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Transcript:

Hello and welcome to this episode of 365 Days of Astronomy. My name is Thomas Hofstätter and I am the host of :: The Hidden Space Project :: at www.hidden-space.at.tf.

[Leon:] And I’m Leon Dombroski from the state of Connecticut in the United States.

[Leon:] Astronomers use a special term to talk about the brightness of stars. The term is “magnitude”. The magnitude scale was invented by the ancient Greeks around 150 B.C. The Greeks put the stars they could see into six groups. They put the brightest stars into group 1, and called them magnitude 1 stars. Stars that they could barely see were put into group 6. So, in the magnitude scale, bright stars have lower numbers.

A star that is one magnitude number lower than another star is about two-and-a-half times brighter. A magnitude 3 star is 2.5 times brighter than a magnitude 4 star. A magnitude 4 star is 2.5 times brighter than a magnitude 5 star.

[Leon:] A star that is five magnitude numbers lower than another star is exactly 100 times brighter. A magnitude 1 star is 100 times brighter than a magnitude 6 star.
Astronomers had to add some numbers to the magnitude scale since the times of the ancient Greeks. We now have lower, even negative, magnitudes for very bright objects like the Sun and Moon. We also have magnitudes higher than six for very dim stars that can only be seen with telescopes.

The brightest star in the sky is Sirius. It has a magnitude of minus 1.4. The planet Mars is sometimes as bright as magnitude -2.8. Another planet, Venus, can shine as bright as magnitude -4.4. The Full Moon is a brilliant magnitude -12.6. And don’t ever look at the Sun. At magnitude -26.8 the Sun’s rays can damage your eyes!

[Leon:] Without a telescope, your eyes can just barely see magnitude 6 stars. The distant planet Pluto is magnitude 14, so you definitely need a telescope to see it. The best telescopes on Earth can spot stars with magnitudes between 25 and 27. The Hubble Space Telescope can sometimes “see” magnitude 30 stars. The low magnitude visible to the Hubble Space Telescope is caused by the fact that it is a space telescope and therefore is not affected by light pollution. This is the reason for astronomers to “flee” into areas without any people living around – such as the Atacama desert in Chile.

There are two kinds of magnitudes for stars. One kind is apparent magnitude. The other is absolute magnitude. Apparent magnitude is how bright stars look to us in the sky from here on Earth. Remember, some stars are closer to us than other stars. A dim star that is nearby looks bright, while a very bright star that is far away looks dim. What if we could line up all of the stars the same distance away to do a fair test of their brightnesses? That is what absolute magnitude is all about.

Astronomers “pretend” to line up stars exactly 10 parsecs (about 32.6 light years) away from Earth. They then figure out how bright each star would look. They call that brightness the star’s absolute magnitude. Our Sun is not an especially bright star. The Sun has an absolute magnitude of 4.83.

[Leon:] These facts all play a role in the annual Great Annual Star Count by Windows to the Universe. This year, the event takes place October 14-28 and everybody is encouraged to spend about 10-20 minutes to participate in the project. Citizens can download star maps that show stars with different magnitudes and compare them to what they see on the clear night’s sky. One of the maps will show exactly the sky as can be seen with the naked eyes. This map then indicates the visible magnitude of the stars. the result can then be reported to the website specifying the place of observation.

This allows to gather data of the regional light pollution to improve available data to fight the recent trend of more and more light pollution as described in an earlier article at the Hidden Space Project. Also, find more information about the Great Annual Star Count by Windows to the Universe at the link-appendix.

That’s it for today. I hope, you enjoyed it. If you have any questions, comments or suggestions, visit me at my website at www.hidden-space.at.tf.

Thanks for listening and clear-skies!
[Leon:] Good bye for now!

New stories are to come soon!

Text by Windows to the Universe and Thomas Hofstaetter.

Links for further information:
• Windows to the Universe
• International Dark Sky Association
• NASA Science Article
• Hidden Space Article

End of podcast:

365 Days of Astronomy
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