If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

## Class 12 Physics (India)

### Course: Class 12 Physics (India)>Unit 9

Lesson 7: Some natural phenomena

# Advanced sunrise & delayed sunset

Why is the sun squashed during sunrise and sunset? Why do we see the sun even before it rises? Our atmosphere is the main cause of this. We will explore these questions in detail.  Created by Mahesh Shenoy.

## Want to join the conversation?

• What causes the apparent flattening of the sun's disc at sunrise and sunset?
• Late reply but I'm bored !

I assume you didn't realize that flattening and squashing means the same, but I'll still answer

1 WORD - ATMOSPHERIC REFRACTION

Explanation

Lower the object from the horizon, higher the shift
so bottom of the sun has more shift than the top part of the sun.
This is the Reason
(1 vote)
• At noon, there's no Advanced or delayed effect.
The question is that where the advanced sunrise ray and the actual sunshine align? Is it at noon? If so, we don't see the actual sunshine till noon because of the atmosphere?
• Yes, we get an illusion of the sun. But, at noon, the light rays from the sun are coming directly above us. So, the atmosphere may cause a slight deviation, but it is much lesser than at sunrise and sunset. So, most likely,it will never align, but come really close to the actual path of the sun during noon.
• Why doesn't the ray bend when it is almost perpendicular?
• Because when its almost prependicular then that ray only acts as a normal and therefore there is no net refraction. Then it doesn't move towards (or away) the normal. And, even how can it do so if it itself is the normal?
• Advanced sunrise and delayed sunset
• Is the time same for when we see a sunrise and for when we see a sunset as we get to see the sunrise earlier and sunset delayed?
• Yes if the actual sun is near the horizon then the time is the same
• So according to this, the SUN moves around the EARTH?!
It might be a silly question, but I am confused.
(1 vote)
• @ Aashi no. When Earth moves Round the Sun, the (light from sun) has to travel varying distances and because of Atmos refraction we see Advanced Sunrise and Delayed Sunset.
• this is the case when the sun is assumed smaller than the earth, but what if it's bigger?
(1 vote)
• what do they then actually mean when they say that the sun rises 8 minutes late(Due to the time taken by light to travel the distance). are they referring to the amount of time takes for light to travel the distance or is it taking this also into account
(1 vote)
• it is given that-"in general the lower the object more is this shifting effect" but also that-" our atmosphere makes the objects appear higher in the sky and the effect is the strongest near the horizon"arent they contradictory. if its near the horizon, wont the object be higher?