I Magnitude where the Pale Dot is blue?

  • I
  • Thread starter Thread starter snorkack
  • Start date Start date
AI Thread Summary
The discussion centers on the color and magnitude of Earth, referred to as the "Pale Blue Dot," as captured by Voyager 1. It highlights that the camera used may not accurately represent the magnitude or color sensitivity compared to the naked eye. Various celestial bodies' BV color indices and magnitudes are compared, with Earth having a color index of +0.2. The conversation also questions whether stars like Sargas and Canopus would appear similar to Earth based on their color indices and magnitudes. Ultimately, the effectiveness of the BV index as a visual response indicator is debated, suggesting that human perception of color may vary with intensity.
snorkack
Messages
2,388
Reaction score
536
Earth is called Pale Blue Dot.
The famous picture of Pale Blue Dot with Voyager 1 from 40 AU is taken with a camera which is not assured to have the correct magnitude or colour sensitivity of naked eye.
As for BV colour indices of planets and one satellite, Wikipedia links to a Nasa report:
https://ntrs.nasa.gov/api/citations/19710009758/downloads/19710009758.pdf
It has more entries, but the major ones:
  1. Sun +0.63
  2. Mercury +0.97
  3. Venus +0.82
  4. Earth +0.2
  5. Moon +0.92
  6. Mars +1.33
  7. Jupiter +0.83
  8. Io +1.17
  9. Europa to Callisto all about +0.85
  10. Saturn +1.04
  11. Titan +1.3
  12. Uranus +0.56
  13. Neptune +0.41
Now compare the brightest stars...
  1. Sirius A0 magnitude -1.46, index 0.00
  2. Canopus A9 magnitude -0.74 index +0.15
  3. Rigil Kentaurus G2+K1 magnitude -0.27 but colour index quoted separately for components - A magnitude +0.01 colour index +0.71, B magnitude +1.33, colour index +0.88. I get colour index for AB approximately +0.75
  4. Arcturus K0 magnitude -0.05 colour index +1.23
  5. Vega A0 magnitude and colour index 0 by def
  6. Capella K0 magnitude +0.08 colour index +0.80
  7. Rigel B8 magnitude +0.13 colour index -0.03
  8. Procyon F5 magnitude +0.34 colour index +0.42
  9. (omitting from now on various A and B stars because they´re all bluer than Earth)
  10. Betelgeuse M1 magnitude +0.50 colour index +1.85
  11. Aldebaran K5 magnitude +0.86 colour index +1.44
  12. Mirfak F5 magnitude +1.82 colour index +0.38
  13. Sargas F0 magnitude +1.84 colour index +0.21
Judging by colour index, Sargas should look like Earth.
At its magnitude, does Sargas look like "pale blue dot"? Does Canopus?
 
Astronomy news on Phys.org
I believe the Blue/Visible (BV) index is used as an index of color temperature and is not a particularly good indicator of expected visual response. The response of the eyeball to color is likely to change with intensity. I have never personally played with it.

/
 
Is a homemade radio telescope realistic? There seems to be a confluence of multiple technologies that makes the situation better than when I was a wee lad: software-defined radio (SDR), the easy availability of satellite dishes, surveillance drives, and fast CPUs. Let's take a step back - it is trivial to see the sun in radio. An old analog TV, a set of "rabbit ears" antenna, and you're good to go. Point the antenna at the sun (i.e. the ears are perpendicular to it) and there is...
3I/ATLAS, also known as C/2025 N1 (ATLAS) and formerly designated as A11pl3Z, is an iinterstellar comet. It was discovered by the Asteroid Terrestrial-impact Last Alert System (ATLAS) station at Río Hurtado, Chile on 1 July 2025. Note: it was mentioned (as A11pl3Z) by DaveE in a new member's introductory thread. https://www.physicsforums.com/threads/brian-cox-lead-me-here.1081670/post-7274146 https://earthsky.org/space/new-interstellar-object-candidate-heading-toward-the-sun-a11pl3z/ One...

Similar threads

Replies
5
Views
5K
Back
Top