by Ann » Thu Jun 02, 2022 5:00 am
It's fun to see the apparent size difference between Venus and the Moon. A math whiz could easily use the apparent size of the Moon versus the apparent size of Venus, to figure out how much farther away Venus is than the Moon, if both are the same size.
But of course Venus and the Moon are not the same size. The size difference between Venus and the Moon is similar to the size difference between the Earth and the Moon, because Venus is just a little bit smaller than the Earth:
It is also interesting to compare the brightness of Venus versus the brightness of the Moon. But I don't think the image does a very good job of showing us their true brightness difference (or albedo, which is a measure of how much of the light that hits them that is reflected by them). Because in reality, Venus is a much, much more reflective body than the Moon, but the true albedo difference is not obvious from the APOD.
Universe Today wrote:
Albedo is a measurement of the reflectivity of an object. A theoretically perfect reflecting object would have an albedo of 1, and reflect 100% of the electromagnetic radiation that falls upon it. While an object that was perfectly black and doesn’t reflect any light would have an albedo of 0. In real life, objects in the Solar System have albedo values between 0 and 1. And in the case of Venus, the albedo is 0.75.
Just for comparison, the bond albedo of the Moon is only 0.12. That’s actually pretty dark. The brightest albedo in the Solar System is Saturn’s moon Enceladus, with an albedo of 0.99. It reflects almost all of the light that falls onto it.
So Venus is perhaps this color:
███, whereas the Moon is perhaps this color:
███
I'm just guessing. Venus is probably not
that bright, and the Moon may not be quite so dark. But you get my point.
Ann
It's fun to see the apparent size difference between Venus and the Moon. A math whiz could easily use the apparent size of the Moon versus the apparent size of Venus, to figure out how much farther away Venus is than the Moon, if both are the same size.
But of course Venus and the Moon are not the same size. The size difference between Venus and the Moon is similar to the size difference between the Earth and the Moon, because Venus is just a little bit smaller than the Earth:
[float=left][img3="The size of the Earth vs. the size of the Moon. Earth image: The Earth photographed from Apollo 17. Moon image: Gregory H. Revera."]https://upload.wikimedia.org/wikipedia/commons/thumb/f/f9/Moon%2C_Earth_size_comparison.jpg/762px-Moon%2C_Earth_size_comparison.jpg?20150509024512[/img3][/float][float=right][img3="The size of Venus vs. the size of the Earth. Image Credit: Venus (left): NASA, JPL, Magellan Project; Earth (right): NASA, Apollo 17"]https://apod.nasa.gov/apod/image/1902/VenusEarth_MagellanApollo17_1080.jpg[/img3][/float]
[clear][/clear]
It is also interesting to compare the brightness of Venus versus the brightness of the Moon. But I don't think the image does a very good job of showing us their true brightness difference (or albedo, which is a measure of how much of the light that hits them that is reflected by them). Because in reality, Venus is a much, much more reflective body than the Moon, but the true albedo difference is not obvious from the APOD.
[quote][url=https://www.universetoday.com/36833/albedo-of-venus/]Universe Today[/url] wrote:
Albedo is a measurement of the reflectivity of an object. A theoretically perfect reflecting object would have an albedo of 1, and reflect 100% of the electromagnetic radiation that falls upon it. While an object that was perfectly black and doesn’t reflect any light would have an albedo of 0. In real life, objects in the Solar System have albedo values between 0 and 1. And in the case of Venus, the albedo is 0.75.
Just for comparison, the bond albedo of the Moon is only 0.12. That’s actually pretty dark. The brightest albedo in the Solar System is Saturn’s moon Enceladus, with an albedo of 0.99. It reflects almost all of the light that falls onto it.[/quote]
So Venus is perhaps this color: [color=#efe7db]███[/color], whereas the Moon is perhaps this color: [color=#594E42]███[/color]
I'm just guessing. Venus is probably not [b][i]that[/i][/b] bright, and the Moon may not be quite so dark. But you get my point.
Ann