[Tron]

Don't tell anybody but I also think Mars is probably smaller then we think.

[stack]

Don't tell anybody but I also think Mars is probably smaller then we think.

Why? It's not just that a gazillion people have gone about various methods to measure planets. The question is, what compels you to think it's smaller than what measurements claim it to be? Is there some internal reasoning you have for why you think it's a different size than reported?

[Tron]

Well yes, it's more of a reasoning method since I could not measure it. Alexandr is doing a good job providing more scientific measuring observations.

[stack]

Well yes, it's more of a reasoning method since I could not measure it. Alexandr is doing a good job providing more scientific measuring observations.

What scientific measurements might those be? Something about measuring a bright spot that is the reflection of the sun? Perhaps sunlight is glinting off of shiny parts of the surface. There are "bright spots" all over Mars. You can't use one to measure anything and trying to do so doesn't fall into any bucket that would be considered a "good job" at providing a "scientific measurement"?

Is it for some reason you just want Mars to be smaller than reported? What's the advantage of hoping it's smaller?

[scomato]

Don't tell anybody but I also think Mars is probably smaller then we think.

Mars has a diameter of 6,779 km. It is 227.9 million km away from Sun. It has a mass of 6.39 × 10^23 kg, an overall density of 3.93 g/cm³, an orbital period of 687 days, and a surface pressure of 0.636 (0.4–0.87) kPa.

What are the measurements of your Mars?

[AlexandrKushnirtshuk]

What scientific measurements might those be? Something about measuring a bright spot that is the reflection of the sun? Perhaps sunlight is glinting off of shiny parts of the surface. There are "bright spots" all over Mars.

There nothing glinting on the Mars' surface accorting to official surface photos of that area. The more - there are no round shaped "bright spots" on the surface of that area of Mars.
1) https://www.google.com.ua/maps/space/mars/@18.4982121,77.6169751,26455m/data=!3m1!1e3?hl=ru

2) https://mars.nasa.gov/mars2020/mission/where-is-the-rover/

[AlexandrKushnirtshuk]

Once again, there is something very strange about the lighting.
1) Reflection of the “Sun” on the surface of “Mars” as if from a searchlight (too small bright spot). The height of the device at the time of this reflection hitting the frame is 9.5 km.
2) This reflection should be exactly under the Sun, that is, perpendicular to the surface of Mars, that is, point exactly at noon, but judging by the smooth movement of the shadow (on the separating heat shield) in the northeast direction (diagonally at 13:30) there is some kind of crap with lighting. The movement of the shadow over the heat shield indicates the position of the Sun in the southwest direction (19:30 hours) relative to the vehicle. The reflection of the "Sun" on the surface of "Mars" indicates the position of the Sun in an easterly direction (15:00 hours) relative to the vehicle.
Perseverance Rover’s Descent and Touchdown on Mars (Official NASA Video)

[stack]

What scientific measurements might those be? Something about measuring a bright spot that is the reflection of the sun? Perhaps sunlight is glinting off of shiny parts of the surface. There are "bright spots" all over Mars.

There nothing glinting on the Mars' surface accorting to official surface photos of that area. The more - there are no round shaped "bright spots" on the surface of that area of Mars.
1) https://www.google.com.ua/maps/space/mars/@18.4982121,77.6169751,26455m/data=!3m1!1e3?hl=ru

2) https://mars.nasa.gov/mars2020/mission/where-is-the-rover/

I have no idea what you're referring to or how a "bright spot" could be measured to reveal the size of planet. Why don't you show us the math you used to make your determination.

[AlexandrKushnirtshuk]

I have no idea what you're referring to or how a "bright spot" could be measured to reveal the size of planet. Why don't you show us the math you used to make your determination.

Here is obvious visual contradiction with the source of light position. What math are you talking about?

This reflection should be exactly under the Sun, that is, perpendicular to the surface of Mars, that is, point exactly at noon, but judging by the smooth movement of the shadow (on the separating heat shield) in the northeast direction (diagonally at 13:30) there is some kind of crap with lighting. The movement of the shadow over the heat shield indicates the position of the Sun in the southwest direction (19:30 hours) relative to the vehicle. The reflection of the "Sun" on the surface of "Mars" indicates the position of the Sun in an easterly direction (15:00 hours) relative to the vehicle.
Perseverance Rover’s Descent and Touchdown on Mars (Official NASA Video)

[stack]

I have no idea what you're referring to or how a "bright spot" could be measured to reveal the size of planet. Why don't you show us the math you used to make your determination.

Here is obvious visual contradiction with the source of light position. What math are you talking about?

This math: "Descent of Perseverance to the surface of Mars. Height (allegedly) 9.5 km. The bright spot on the surface is the reflection of the Sun. Can there be such a reflection on the surface of a sphere with a diameter of 6.7 thousand km, or the diameter of Mars is about 15-20 km?"

How'd you come up with 15-20 km? And what's wrong with a bright spot? What does that have to do with anything.

This reflection should be exactly under the Sun, that is, perpendicular to the surface of Mars, that is, point exactly at noon, but judging by the smooth movement of the shadow (on the separating heat shield) in the northeast direction (diagonally at 13:30) there is some kind of crap with lighting. The movement of the shadow over the heat shield indicates the position of the Sun in the southwest direction (19:30 hours) relative to the vehicle. The reflection of the "Sun" on the surface of "Mars" indicates the position of the Sun in an easterly direction (15:00 hours) relative to the vehicle.
Perseverance Rover’s Descent and Touchdown on Mars (Official NASA Video)
[img = 200]https://i.ibb.co/Jk3GxHx/ezgif-3-cc50997a6900.gif[/img]

Why should the reflection be exactly under the sun? Why noon? Noon on Mars?

How do you know the sun is southwest? Southwest in relation to what? How do you know where the sun should be?

[AlexandrKushnirtshuk]

[AlexandrKushnirtshuk]

Link to the answer about location of source of light on the Perseverance landing video:
https://www.scienceforums.net/topic/124460-lighting-questions-on-the-perseverance-landing-video/?tab=comments#comment-1169450

Ghideon from scienceforums.net:
@AlexandrKushnirtshuk you may look a few seconds further into the video you linked to. The heat shield is probably just wobbling after being dropped? That makes the heat shield look oval from the camera's point of view and reflections are moving.

Question about the size of sun spot reflection.
Sorry for the many images, but they are all necessary.
Is it possible to explain such a small size sun reflection on the surface of Mars? Yellow dot on the image below is the size of Jezero Crater on Mars. Bright spot on the animation below is reflection of the Sun (from Perseverance landing video), which located inside the Jezero Crater and makes up no more than 10% of the area of Jezero Crater. Last (third) image shows how sun reflection spot looks like on Earth's surface.



Location and size of bright spot (Sun reflection), from animation above, inside Jezero Crater. That bright spot is not in the middle of the crater, and there is nothing bright in that area on two photos of that area, which are posted in Reply #25 of this thread.

[stack]

You answered none of the questions.

[AlexandrKushnirtshuk]

Bright spot is an evidence of the sphericity and size of the sphere, respectively. I think there can be no other explanation.


But in that case, the shadow on the animation below should move in the diametrically opposite direction.

[stack]

Bright spot is an evidence of the sphericity and size of the sphere, respectively. I think there can be no other explanation.


But in that case, the shadow on the animation below should move in the diametrically opposite direction.

Seriously? You can determine the size of Mars based upon a "bright spot"? What was your calculation to do so?

[JSS]

Bright spot is an evidence of the sphericity and size of the sphere, respectively. I think there can be no other explanation.

There is actually another explanation.  You could be seeing a specular highlight, which can be seen on any shape, even a flat plane will produce them.

[AlexandrKushnirtshuk]

Sun reflection on Earth from 400 km. and Mars from 10 km.

ISS animation source: Over Earth - Incredible Space Views from ESA Astronaut Alexander Gerst

[AlexandrKushnirtshuk]

Artist’s impression of Mars four billion years ago (video title from YouTube)


Size of Jezero Crater on Mars, and size of Sun reflection inside that crater, which makes up less than 10% of Jezero Crater area.



Same bright spot size on Curiosity landing video.
Complete Mars Curiosity Descent - Full Quality Enhanced HD 1080p Landing + Heat Shield impact (video title from YouTube)

[stack]

Artist’s impression of Mars four billion years ago (video title from YouTube)


Size of Jezero Crater on Mars, and size of Sun reflection inside that crater, which makes up less than 10% of Jezero Crater area.



Same bright spot size on Curiosity landing video.
Complete Mars Curiosity Descent - Full Quality Enhanced HD 1080p Landing + Heat Shield impact (video title from YouTube)

So what's your calculation based upon this "bright spot"? How big is Mars?

[AlexandrKushnirtshuk]

So what's your calculation based upon this "bright spot"? How big is Mars?

Mars diameter is about 15-20 km., based on my approximate calculations regarding the ratio of the diameters of the Earth, the Sun and the Moon, given at the beginning of this forum topic (thread).

Asked that question on NASA forum: https://forum.nasaspaceflight.com/index.php?topic=53173.0