is it possible to take clear night sky shots with stars/ planets visible from Redmi Note 4? what settings do I use? when I try to take it just comes black, unless on full moon day with HDR, though stars like Orion's belt won't get captured. Would using a telescope make celestial objects much clear to capture?
Astrophotography is a much more complex process than you might expect it to be.
The stars do put out a lot of light, but it's pretty well diffused by the time it hits Earth. You would need a long exposure (about 1 minute) shot multiple times, each time checking the alignment to make it work.
Most astrophotography uses multiple shots taken over several hours and composited in software. The telescope has to be moved to track the objects or you will end up with trails.
In short, you really do need a telescope at best (and need to understand how to use it), or an SLR either film or digital with a decent lens that you can set to infinite focus.
I've shot stars on a film camera using a 55mm prime lens, and did 3 minutes shots on ISO 400 film. They looked ok, not great but ok. If you're using a digital camera, you will need to keep in mind that sensors heat up with continuous use.
If shooting with an SLR, you need to get to the site you're shooting from while it's still light and focus on some clouds. Often, you can get away with setting your lens to infinity, but many lenses have an infinity point which is not quite infinite. Focussing on the stars in the dark is like knitting with smoke, so you need to be there early.
Phone cameras are really not geared up for any niche uses. They're the perfect snappy cameras for capturing a moment, and as most of the time you have your phone with you, it really is a great tool. It's not got the versatility needed for astrophotography as it stands though, and you would struggle to find any phone with appropriate settings to make it possible, let alone get good results without some additional hardware.
Essentially, it comes down to the ability of the device to capture light from a long distance away. The lens and sensor on a phone are pretty small and would struggle to let in sufficient light to get really clear shots as it stands.
As Michael Clark has pointed out in the comments, a smartphone can be used with a telescope to capture some high quality photos, as the telescope is very capable of capturing enough light to be readable by the sensor.
Where the phone may cause issues is in setting the sensitivity to be sufficient to capture light quickly. In many tutorials for astrophotography using DSLRs, it is recommended to set the ISO level quite high (3200 or 6400) so as to reduce the time taken during the exposure. As high ISO captures less detail, compositing the shots is necessary to produce a clear image. I've never encountered a phone which allows ISO setting changes manually (I can't find any details on the Redmi Note 4 on this point), but this might not be necessary if your telescope produces a bright enough image at the eyepiece. If you don need to shoot long shots with the phone, you might need to find a way to secure it to the telescope so as to prevent shaking.
I would also suggest that you use the timer when taking the shot. For my longer exposures, I used a remote release to keep from shaking the camera, but for shots taken on a second camera with up to 30 seconds exposure available, I used the timer as I had no remote trigger for it. Just pressing the shutter shook the camera and led to some very messy trails, however setting a 5 second timer was enough to allow me to trigger the shot, and give enough time for the tripod to stop wobbling.
From my experience so far with photographing stars, I have learned that you should not underestimate the task. I found a lot of issues cropping up which I simply didn't account for - the stars move a lot faster than you realise, and wind shake is definitely noticeable even on a very calm night.
If you want to get it right, have a look at this site which will tell you everything you need to know to get started - http://www.astropix.com/html/i_astrop/quick.html
As an aside, that link is the very first result from a google search for "getting started with astrophotography". It's worth having a look around online before posting, as in many cases if the answer can be found quickly, people will be less inclined to reply.