Questions tagged [angular-diameter]

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What does the Sun look like from the heliopause?

I calculated the angular diameter of the Sun at the heliopause to be 0.004°. If that is correct, would the Sun appear as a disk, or like the pinpoint of light from a star? How bright would the ...
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2answers
198 views

From what distance would our sun have an angular diameter of 7 arc seconds?

If an observer travels away from our sun, at what distance would our sun occupy 7 arc seconds of space?
2
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1answer
107 views

How would a flat mirror on the Moon reflect sunlight

I was solving a task that said (paraphrasing): There is a flat mirror on the Moon, whose reflection coefficient is 100%, and observers on the Earth observe it as a star whose apparent magnitude is $...
4
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1answer
632 views

Angular Diameter Distance

The definition of the angular diameter distance is the ratio of an object's physical transverse size to its angular size. However when I was reading my textbook, Astrophysics in a Nutshell by Dan Maoz ...
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0answers
253 views

How big is the Andromeda galaxy in the night sky? [duplicate]

If divide the distance to the sun by its diameter, I get the number 107.517 Likewise, if divide the distance to the moon by its diameter, I get the number 110.650 Both numbers are quite similar which ...
2
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1answer
743 views

Understanding The Turnover Point of Angular Diameter Distance

I am trying to get a better understanding of cosmological distances, in particular the angular diameter distance which I have also seen referred to as angular size distance. What I am looking for is ...
2
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1answer
172 views

Does the given radius of a planet/moon include its atmosphere?

In NASA fact sheets, such as this one for Venus, a radius of the planet is given. Is that radius the radius of the surface of the planet, or of the envelope of atmosphere? Put another way, if ...
1
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1answer
323 views

How do we get the angular size of a crater without lens?

Suppose I want to calculate the diameter of the crater. I apply the small angle formula $$diameter=\frac{\theta_{diameter}}{206265''}\times D$$ where $\theta_{diameter}$ is the angular size of the ...
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0answers
59 views

Calculating angular diameter amplitude from angular diameter variations of Cepheid variable

I'm a high school student but have as much interests in Cepheid variable as the professionalists. I'm trying to derive independent distances to Cepheid with the Baade-Wesselink method. I got the ...
0
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1answer
52 views

How do I get the change in angular diameter value?

Given that I got the equation relating the angular diameter(θ) and $V$–$K$ band value, which is known as $\logθ_0=(0.262±0.004)(V−K)_0+(0.547±0.006)$ from this paper, how do I get the 'change' in ...
2
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0answers
53 views

Using the surface-brightness relation for Cepheids

I'm a high school student who is doing research about Cepheid variables. I'm in the process of deriving distance to Cepheid using the Baade-Wesselink method, which utilises the surface brightness ...
1
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0answers
50 views

Change in angular diameter of Cepheid variables

I'm a highschool student and in the process of writing a research paper of deriving period-lumniosity relation of Cepheid variable independently of the pre-existing PL relation. Thus, I need to derive ...
5
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1answer
3k views

What is the angle between the equator of the sun, and the plane of the Earth's orbit

I want to know the angle between the plane that passes through the centre of sun and is perpendicular to its spin axis, and the plane that contains the orbit of earth around sun? Is this a fixed ...
4
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3answers
1k views

Do objects look larger the further away they are, beyond z=1?

I stumbled upon this text which illustrates and says: We find that as the object is moved to higher redshifts its angular size first decreases (as naively expected) but soon begins to increase ...
6
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3answers
15k views

What is the angular diameter of Earth as seen from the Moon?

...today I must have left my brain home. I know it's a simple calculation but I keep failing simplest calculations today. What is the angular diameter of Earth as seen from the surface of the Moon?