#angular diameter

Ask Ethan: Do Ancient Galaxies Get Magnified By The Expanding Universe?

“Do ancient galaxies appear larger to us than they really were, due to the expansion of the Universe? If so, then by how much?”

It seems like the simplest, most straightforward idea in the world: the farther away an object is, the smaller it appears. View the same object when it’s twice as far away, and it will only appear to be half as large in terms of angular size. Place it ten times as far away, and you’ll see it appear just one-tenth the size. 

But this is only true in flat, static space. In the expanding Universe, this relationship falls apart, particularly when you factor in dark energy. More distant objects appear smaller the farther away you look, but only to a point. Galaxies that are about 14-to-15 billion light-years away will appear the smallest, and then the same-sized galaxy will actually appear larger the farther away you look! This may be counterintuitive, but there’s real, solid science to back it up. 

उत्तर भारत के कुछ हिस्सों में रविवार को पूर्ण कुंडलाकार सूर्यग्रहण देखा जाएगा

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एक कुंडलाकार सूर्य ग्रहण, जिसमें सूर्य आग की अंगूठी की तरह दिखाई देता है, रविवार को देश के कुछ हिस्सों में दिखाई देगा, पृथ्वी विज्ञान मंत्रालय ने कहा।

ग्रहण का आंशिक चरण सुबह 9.16 बजे शुरू होगा। कुंडलाकार चरण सुबह 10.19 बजे शुरू होगा और दोपहर 2.02 बजे समाप्त होगा। ग्रहण का आंशिक चरण अपराह्न 3.04 बजे समाप्त होगा।

एस्ट्रोनॉमिकल सोसायटी ऑफ इंडिया ने कहा, “दोपहर के करीब, उत्तर भारत में एक…

One of the things I wonder about sometimes is just how things like the mega-structures in some science fiction might look from Earth.

What you see in the image is a pair of cylindrical orbiting habitats roughly 1 km in radius and 2 km in height, along with a 125 km coilgun intended to launch payloads clear out of Earth orbit at human survivable accelerations.

The structure is eclipsing the moon, and the relative sizes should be reasonably accurate for a person standing on the equator looking up at the structure 500 km directly above.

Here’s a closer look, with the positions changed a bit so the moon is more visible.

Why Moon Is Not Bathed In Earth-shine In Solar Eclipse

A solar eclipse is a natural event that takes place on Earth when the Moon moves in its orbit between Earth and the Sun (this is also known as an occultation). It happens at New Moon, when the Sun and Moon are in conjunction with each other. If the Moon was only slightly closer to Earth, and orbited in the same plane and its orbit was circular, we would see eclipses each month. The lunar orbit is…