## Astronomy C

PM2017
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### Re: Astronomy C

As for images, yes, all the images (they're pretty too!). Hope this helps, please keep questions coming if that was confusing!
Just adding to this, you should also label each image (we include Telescope, Wavelength, Date if important, and for the non-obvious images, we include a description. By non-obvious I mean like the supernovae inside a DSO.)
West High '19
UC Berkeley '23

Go Bears!

GarethM
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### Re: Astronomy C

What reference value should be used for apparent/absolute visual magnitude? I can find luminosities for all wavelengths, but not just visible wavelengths.

Unome
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### Re: Astronomy C

What reference value should be used for apparent/absolute visual magnitude? I can find luminosities for all wavelengths, but not just visible wavelengths.
Your question is a little unclear. What sort of reference values are you looking for?
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GarethM
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### Re: Astronomy C

I’ve seen questions that ask to convert absolute visual magnitude to visible luminosity measured in watts. I understand that a decrease in 5 magnitudes is a 100x increase in brightness, but I don’t understand what that increase is measured from, i.e. what value is defined as 0 on the magnitude scale. I was thinking I could measure relative to a star with a known absolute magnitude and visible luminosity, but I can’t find information on the visible luminosity of any stars. I’ve found info on bolometric magnitudes for all wavelengths, but nothing for just visible.

I’m basically wondering how to calculate visible luminosity in watts when given absolute visible magnitude.

Unome
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### Re: Astronomy C

I’ve seen questions that ask to convert absolute visual magnitude to visible luminosity measured in watts. I understand that a decrease in 5 magnitudes is a 100x increase in brightness, but I don’t understand what that increase is measured from, i.e. what value is defined as 0 on the magnitude scale. I was thinking I could measure relative to a star with a known absolute magnitude and visible luminosity, but I can’t find information on the visible luminosity of any stars. I’ve found info on bolometric magnitudes for all wavelengths, but nothing for just visible.

I’m basically wondering how to calculate visible luminosity in watts when given absolute visible magnitude.
My typical method is to take the Sun's absolute magnitude of around 4.85 and use its known luminosity in watts to convert.
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Chattahoochee High School Class of 2018
Georgia Tech Class of 2022

Opinions expressed on this site are not official; the only place for official rules changes and FAQs is soinc.org.

PM2017
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Posts: 491
Joined: January 20th, 2017, 5:02 pm
State: CA

### Re: Astronomy C

I’ve seen questions that ask to convert absolute visual magnitude to visible luminosity measured in watts. I understand that a decrease in 5 magnitudes is a 100x increase in brightness, but I don’t understand what that increase is measured from, i.e. what value is defined as 0 on the magnitude scale. I was thinking I could measure relative to a star with a known absolute magnitude and visible luminosity, but I can’t find information on the visible luminosity of any stars. I’ve found info on bolometric magnitudes for all wavelengths, but nothing for just visible.

I’m basically wondering how to calculate visible luminosity in watts when given absolute visible magnitude.
My typical method is to take the Sun's absolute magnitude of around 4.85 and use its known luminosity in watts to convert.
I do this as well.
West High '19
UC Berkeley '23

Go Bears!

jz123sst
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### Re: Astronomy C

Does anyone know if Astronomy will still be an event 2019-2020 (next year)? If so, what topics will it cover?

pb5754[]
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### Re: Astronomy C

Does anyone know if Astronomy will still be an event 2019-2020 (next year)? If so, what topics will it cover?
It definitely will be an event next year, and I'm not sure but I think the topic will be variable stars or star/planet formation.

jz123sst
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### Re: Astronomy C

So stellar evolution is a topic every year?

pb5754[]
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### Re: Astronomy C

So stellar evolution is a topic every year?
Yes... like there is a 99.9% chance I would say.