# All Questions

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100 views

### Can a planet exist with the same mass as the earth, but have a different diameter?

Can there be a planet with the same mass, and a similar composition, as the earth, but with a larger or smaller diameter, and how could that theoretically occur? I've tried to see if there is any ...
3k views

### How do we know Nemesis is not a black hole (or neutron star)?

Nemesis, the hypothetical "death star", is supposed to be a massive body that orbits the Sun at long distances and periodically sends comets from the Oort Cloud into the inner solar system. These ...
100 views

### Cosmological redshift - How do we know it's not caused by the observer's time dilation?

Instead of cosmological redshift being caused by the metric expansion of space, why couldn't cosmological redshift be caused by our perspective moving faster in time? Said another way, if the ...
51 views

### What is the apparent magnitude of the faintest stars visible during a full moon?

Assuming the viewer is far from any light pollution, it is a cloudless night, and humidity is very low. What is the faintest apparent magnitude of stars visible to the naked eye during a full moon (...
27 views

### Are there any openly available simulators describing how planets form from protoplanetary disk?

Out of pure interest, I wonder whether there are existing open-source simulators that can simulate the formation of stars and planets from a protostar and the surrounding protoplanetary disk?
74 views

### Does the Lagrange L1 point have a 'size'?

Like in cubic kilometers, what is the size of L1 "area of influence"? being unstable I guess that size can vary?
125 views

### Minimum Telescope Needed to See Saturn's Rings

I am a total novice. My daughter, likes Saturn. Since Saturn is so close I thought it was a good time to view it with her. What are the minimum needed telescope specs? GC Update: Can answer ...
241 views

### Is there any site with telescopes data?

Is the data gathered from telescopes "open source"? If so, is there any website that group it all?
37 views

### Use of an Equatorial Mount [duplicate]

What is Equatorial Mount in simple terms? What is polar alignment? What will happen if we use an Equatorial Mount without polar alignment? And if we polar align how can we point at other stars?
39 views

### Where can I find the previous years' International Astronomy Olympiad question papers?

I have looked at the official site but the link for previous papers isn't working.
79 views

### How much infrared radiation is emitted by a bow shock?

Has the amount of energy being emitted from R Hydrae's bow shock been studied? If so, is there any information how much infrared radiation is emitted in any means of measurement? If the infrared ...
51 views

### Counter clockwise rotation of storms at Jupiter's north pole. What explanations have been proposed?

On Earth, high pressures and low pressures occur interchangeably. So that where two pressure systems intersect, they move the air in the same direction. But as Juno revealed the first observations of ...
39 views

### IAO 2015 Question 1 Noon at the Olympiad

Yesterday, on October 16, 2015, the upper culmination of the Sun at the venue of the Olympiad was at 11:29:44 local time. Calculate as accurate as possible at what time the upper culmination of the ...
8k views

### Would an object shot from earth fall into the sun?

Would an object shot from earth fall into the sun? If an object is shot at 107,000 km/h via rocket or otherwise, in the opposite direction to our orbit about the sun, it will be traveling at 0 km/h ...
252 views

### Why is ice on Mars not covered in dust?

There's exposed water ice on Mars, like in craters like this At the same time, Mars has dust storm, covering the solar panels of rovers, and occasionally covering the entire planet So why is this ...
1k views

### If a spaceship ran out of fuel somewhere in space between Earth and Mars, does it slowly drift off to the Sun? [migrated]

Pretty much what the title is saying. I feel like I am missing something fundamental here and this is driving me crazy. Does a spaceship which is out of Earth's gravity drift to the Sun eventually?
36 views

### Derivation of a formula for the mass of a tidal bulge and tidal torque

I've been looking into the tidal mechanism for a binary star system and seem to have hit a brick wall. In the literature (see below), little explanation is given to justify the equations (9.60), (9.61)...
54 views

### How does the number in stellar classification indicate properties within the range of that class?

I am doing some research for a video game and I wanted to store stellar data on a star, such as its Stellar Classification, and then from that derive a physical appearance in the game. These are ...
341 views

### Is the resulting light from a supernova a product of photons bouncing around in the Sun?

I was thinking about how photons formed in the centre of the Sun take quite a long time to exit the surface. And it occurred to me that at the end of a star's life (during a supernova, given that it's ...
144 views

### How does time work beyond the cosmic event horizon?

The faster you move through space, the slower you move through time - the calculations show that as you approach lightspeed, time comes to a standstill. How does time work beyond the cosmic event ...
40 views

### mm-wavelengths Moon map, scientific case

I would like to test a telescope with a Moon observation. It is a low spectrometer-imager at 110-300 GHz with a resolution of 4 arcmin@150 GHz. Is there any scientific target that concerns the Moon ...
107 views

### Visitors that became satellites?

To anyone's knowledge, has there ever been an object that approached the earth and was captured into an orbit? Is it thought that there might be such objects simply too small to spot or just not ...
93 views

### Propagate Earth trajectory for 1 Myr

What is the most accurate way of propagation of Earth trajectory relatively to the Sun? I need to calculate the Earth-Sun distance. Is there any library on Python? I've used before JPL Horizons, ...
69 views

### Moon changes position

So most nights the Moon usually rises on the right of the sky when I look through the window just like the previous night. But this night the Moon was on the left of the sky rising. Does anyone know ...
50 views

### Does the spin rate of a black hole correspond to a physical feature?

If the mass and orbital period for two neutron stars is known before collapse to a black hole and the rate of spin is known after collapse, 100 revolutions per second for instance, that will correlate ...
60 views

### The energy density of DM (to be fluid,state parameter=-2)increases with time. Does it violate the concept of accelerating universe?

We know that dark energy with value of state parameter $\omega<-1$ is called phantom dark energy model. In this model if we assume dark energy to be a fluid with value of state parameter $\omega=-2$...
53 views

### How many Moon's Topocentric Conjunction occurs per lunar month?

It is clear that only one Moon's Geocentric Conjunction occurs per lunar month, what about the Topocentric Conjunction for a given location? without scale I can imagine many Topocentric Conjunctions ...
65 views

### How to calculate phase angle of a satellite?

I'm making a program for predicting satellite passes. I'm trying to find out if the satellite is illuminated by the Sun and not in Earth's shadow. I need to know its phase angle: the angle between the ...
64 views

### Could there be a M-type asteroid beyond Jupiter?

Is there any reason to think an M-type asteroid could not have migrated beyond Jupiter and entered an orbit similar to the Centaurs?
122 views

### What do the fusing 'onion layers' of a pre-supernova star look like to scale?

I'm sure we've all seen the diagrams of various layers of element fusion from hydrogen to silicon in a star that's just about to go supernova. (Picture from courses.lumenlearning.com) I suspect ...
32 views

### How many parent stars contributed to our solar system? [duplicate]

All of the stuff that isn't hydrogen and helium (which came from the Big Bang), that coalesced to form our solar system (the iron, the sulfur, the water, and so forth) all came from previous ...
166 views

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### Get a table of Moon phase angle per day

Where can I get a table with the Moon phase angle for each day ? It's available here for a given day, but I would have to input each day of a year to get a full table. === NEW EDIT : 2019-09-18 ===...
124 views

### How much volume of gases could be added to Mars atmosphere that the planet gravity can retain?

This article Mars atmosphere states that Today Mars atmosphere is very thin, but it was not always like this. Around 3.5 billion years ago, the red planet had a thick enough atmosphere for liquid ...
59 views

### Formation of the First Stars

I've got a few questions about the first stars to form in the universe. First off how might metalicity have impacted the formation of the first stars and also what effect would the absence of metals ...
6k views

### Is it possible that the shadow of The Moon is a single dot during solar eclipse?

During a solar eclipse The Moon covers The Sun on some places on the Earth. Now the focal point is a bit above the Earth so the shadow area is about 160 miles. In history The Moon was a bit closer to ...
117 views

### Cosmological redshift vs doppler redshift

I'm reading Harrison's "Cosmology: Science of the universe" because Harrison focuses on the distinction between cosmological redshift (he calls it expansion redshift) and the Doppler redshift. He ...
97 views

### What is a black hole's “shadow” and the best angle to view it to measure the spin?

This excellent answer mentions several ways to try to observationally measure the spin of a rotating black hole. The third one is intriguing, but I don't understand how this works: The spin of a ...
199 views

### When did people discover that the Earth is not an ideal sphere, but a little flattened?

When did people discover that the Earth is not an ideal sphere, but a little flattened? And if you know, who was the first person to discover it?
24 views

### Dispersion: any software to work out the dispersed waveforms of EMW signals that propagate via interstellar medium for some distance?

Is there any software (toolbox, code, package, paid or opensource are both ok), to work out the dispersed waveforms of EMW signals (time series data are given), that propagate via the interstellar ...
42 views

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### Does the Sun have a numerical designation in any star catalogues?

Given the existence of large star catalogues listing millions of astronomical objects with numerical designations (such as Tabby's Star, KIC 8462852) it occurred to me that one of them might contain ...
205 views

### Can we see evidence of sunspots on other stars

Searching for exoplanets by measuring the change of a stars brightness when an exoplanet transits the star's disk also has the potential to detect exo-sunspots. Have they ever been detected?
108 views

### Estimate prevalence of ʻOumuamua-style interstellar obects inside Jupiter orbit now that C/2019 Q4 (Borisov) is found?

Now we know two of them, so maybe it's not an outlier. We have two points so we can draw a line. How many similar macroscopic objects should be zipping through space at ~30 km/sec so that we would ...
24 views

### Redshift, velocity, distance

How are redshift, (recessional) velocity and distance of a galaxy related? I understand what v=HD states. So I assume that Hubble measured a direct relation between the distance and recessional ...
577 views

### Can I see Harvest moon in India?

I just saw articles which say the Harvest moon will be visible in the US. Apart from the US, in which other country can people see it? Can I see it from India?
35 views

### How to model and subtract nebular emission lines from stellar spectrum

I have optical stellar spectra from a star forming region with spatially varying nebular background. I want to subtract the nebular lines from the stellar spectra (which are varying in intensity from ...