# All Questions

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### How to see Mars and Venus in color?

My telescope is Arsenal - Synta 70/700 AZ2 (refractor model). 140x max zoom (10 mm with Barlow). I could clearly see Jupiter and Saturn in color. I even saw brown stripes on Jupiter. Yet, when I tried ...
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### can moon rise before sun and set after it in the same day

I found it mentioned in ancient Arabic astronomic book Kitāb al-Amwāl by Ibn Qutaybah (889 AD) Cresent can't be seen in the morning in the east in front of the sun and in the evening i the west ...
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### What is the mass and momentum of a relativistic jet?

Relativistic jets from accreting black holes are powerful radiation sources, but carries some ionized matter along. What are the estimates or observations of the mass or momentum flow in such jets?
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### What satellite is this?

While out viewing the Perseid shower last night (8/11/20), we saw an interesting object that I'm trying to identify. We're in the vicinity of Portland, Oregon. It appeared to be traveling west->...
19 views

### Determine spectral type of star from its properties

How can I determine spectral type of star, if I know all its another properties? For Example, Rigel A has spectral type B8Ia. Rigel has temperature 12 500 K. ...
25 views

### How can one determine the angle between the line of nodes and the major axis of the orbit of Mars?

I know when northern summer is on Mars, the solar radiation on its surface has a minimum of 492 W/m², meaning that is also the time when Mars is furthest from the Sun. So this would coincidence ...
26 views

### Question about semi-major axis mean separation

I am currently doing an assignment but I cannot for the life of me understand what one of terms used means. Notice I am not trying to get help with the assignment itself, but rather to make me ...
1k views

### What color is a red dwarf star?

I read recently that a red dwarf star might actually look white. I realize there's a wide range in red dwarf surface temperature, 2,500 to 3,500 degrees K, compared to 5,778 for our Sun. Metal at ...
23 views

### How can I estimate the initial luminosity of a SNIa given initial mass of Ni-56?

The initial portion (and peak) of a SNIa's light curve is powered by the $\beta$-decay reaction: $$^{56}Ni \rightarrow ^{56}Co + e^+ + \nu_e + \gamma$$ Supposing we know how much Ni-56 is created in ...
35 views

### Celestron C14 collimation and cleaning

When checking the collimation of a Celestron 14" SCT I took this image: My question is: how much will the particles causing the local aberrations affect the image quality? (i.e. do I need to ...
57 views

### How did we measure the mass of the universe?

In an wiki article, observable universe, it was mentioned that, Mass (ordinary matter) 1.5×10^53 kg I wonder how did we measure the mass of our observable universe?
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### Can a telescope ever increase the apparent luminance of an extended object?

From what I know about common telescope designs, telescopes don't increase the apparent luminance of extended objects compared to the luminance seen with the naked eye. In this sense extended objects ...
49 views

### How much (more or less) of the moon will be visible as it recedes from the Earth?

The Moon is receding from the Earth, at a rate of about 4 cm per year. We can currently see about 59% of the Moon's surface, from the Earth's surface. Will the amount of the Moon's surface we can see ...
13 views

### Why is the peak value(s) of the spectral radiance of the CMB different if you calculate with freq. instead of wavelength?

On Wikipedia, the calculated value of the peak frequency of the cosmic microwave background is 160.23 GHz, but it says if you do the calculating with wavelengths, then convert to frequency, you get a ...
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### What was the energy/wavelength/frequency of the CMB when first emitted/released?

Given the z redshift of 1089, and the temperature difference between then and now of about 1089, I tried scaling the ev, freq. and wavelength by 1089.... Is that right? I get a freq. of about 240 ...
3k views

### How much does the sky change in a few thousand years?

The "fixed stars" are not actually fixed, the earth's tilt changes over time etc., but all that happens slowly on human timescales. Imagine a Babylonian astronomer (or astrologist?) ...
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### 360 degree image of the whole sky

I look for an image that I know exists. It is an image showing the whole sky, showing all stars and galaxies bright enough to be visible at the resolution, projected to the same shape that is commonly ...
122 views

### If the solar system is nearly flat, then why don't all the planets appear to lie on the same axis when viewed from earth?

For instance, consider the image below. The location of the planets seem to be so random relative to Earth. If the solar system was indeed flat, then I would expect the planets to lie on the same '...
41 views

### Picking two random points in space and drawing a line between them, what is the chance the line intersects anything?

I thought of this question after pondering how most of the observable universe is observable. If we can observe it, then the space between us and that object must have been unoccupied to allow the ...
29 views

### How can I calculate the uncertainties in magnitude like the CDS does?

When you check an entry of the Gaia DR2 stellar catalogue in Vizier, for example this one, you can see that there is a value for the G magnitude (in our case 18.0733 mag) and a value for the ...
4k views

### Why can't we see Saturn's phases from earth?

In the Astronomy Picture of the Day from August 8, 2020 ("Crescent Saturn"), the caption states From Earth, Saturn never shows a crescent phase Why is this? We can observe phases on ...
46 views

### Timekeeping on other celestial bodies than Earth

I have looked for months for any site capable of calculating solar altitude w.r.t an observer located on the surface of a generic celestial bodies, but with no luck as of now. Even NASA does not ...
47 views

### Black Hole - energy and matter

Can someone explain what is happening with energy (e.g. light) and matter which was collected by a black hole? I suppose that matter builds a black hole's mass and size, but what about light? Does it ...
26 views

### Problem 7- chapter 13 of the Astronomy Principle and practice.-Calculate the radius of Venus

Well, this is one of the exercises from chapter 13 of the Astronomy Principle and Practice, which using Kepler's Laws to solve it. But if there are other ways to solve that would be great. Thank you!
62 views

### How does a cross dispersed spectrum look like in a reality (from echelle spectrographs)?

I am an analytical chemist with some interest in amateur spectroscopy. Since astronomers use echelle spectrographs to study the high resolution spectrum of the stars, someone suggested to post the ...
1k views

### Shouldn't tidal locking be impossible for a satellite that has a considerably eccentric orbit?

This popped up into my mind just now. The Moon is tidally locked to Earth, and also has a significantly eccentric orbit. This means that its orbital velocity near periapsis is considerably faster than ...
480 views

### What is meant by “vastness of space, which now filled a volume of a hundred million light years”?

I am reading the book Cosmic biology: How life could evolve on other worlds (citation below) and do not understand the meaning of the following paragraph from page 4 (emphasis mine): It took 200,000 ...
2k views

### Where is the Perseids meteor shower coming from?

Swift–Tuttle Comet has orbital period of 133.28 years. Yet, people say that debris and dust from this comet causes this meteor shower. This does not make any sense. Or do they want to say that from ...
50 views

### Strange trail left by shooting star [duplicate]

I saw something really odd last night that I cannot understand. Last night I got up around 3am to catch a glimpse of the upcoming Perseids meteor shower, now I know it's not peaking until next week ...
189 views

### Are all solutions of the 3-body problem restricted to 2 dimensions?

I am not a physicist. Suppose there are two massive bodies orbiting each other. Their orbit will presumably define a plane. As far as I know, the existing solutions to the 3-body problem are limited ...
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### Why can there be several seconds of lag between a binary neutron star merger and the emission of gamma rays from the same area?

Answers to: Gravitational waves and gamma ray burst: how were the error bars determined for this speed of gravity calculation? Was $H_0$ used? go into substantial detail explaining this determination. ...
81 views

### how long a light year on earth will seem [closed]

First of all, sorry if this is not the right StackExchange to ask this question, but i don't know a better place (open to suggestion in case). So, the question: Suppose that for some reason, we can ...
87 views

### Impact on the rest of the solar system if Mercury or Venus were disassembled?

I've watched a few theoretical videos about Dyson spheres where they mention that the most practical way to do that would be to disassemble a planet - preferably one already close to the sun - Mercury ...
50 views

### Can an event horizon form with the observer already inside?

I am on a planet orbting a star around the center of the milky way (assume no supermassive blackhole there). By some mechanism, mass starting from the outer part of the galaxy gets pushed inward until ...
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### Events I cannot explain

In the last few days I experienced two events I cannot explain. I watch the sky since I was a child so I'm aware of most events like satellites, ISS, Iridium flares, etc... First event It was about 22:...
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### How did the orbits of Phobos and Deimos circularize?

The satellites of Mars might be captured asteroids. But Phobos has an eccentricity of $0.015$, and Deimos of $3\times10^{-4}$. If they were captured, they likely were captured with rather eccentric ...
461 views

### Gravitational waves and gamma ray burst: how were the error bars determined for this speed of gravity calculation? Was $H_0$ used?

This newly updated answer to How precise are the observational measurements for the speed of gravity? and this answer to How is the most accurate value of 𝐺 measured? cites the November 2017 arXiv ...
60 views

### Trying to use Canon 60D DSLR with Skywatcher 130P. Can't focus image

I have a Skywatcher Heritage 130P FlexTube Dobsonian Telescope. It works well, I can see lovely stars, planets, moons of Jupiter etc. It came with two eye pieces (1.25 inch): 10 mm and 25 mm. I also ...
42 views

### Why is our heliosphere an asymmetric croissant shape?

The big, recent astronomy news about our heliosphere's asymmetric croissant shape has me confused.... Some articles mention the influence on our solar system's outermost boundary of very hot cations, ...
46 views

### Angular diameter result confirmation

Not being a math-minded person at all, however basic it might appear to be to all of you in this particular question, I would like to get the following calculation confirmed. I'm trying to calculate ...
77 views

### 50mm f1.8 for Astrophotography

I am considering using a 50mm f1.8 maybe even try aN 85mm f1.8 on my Astro FI 102MM Telescope have you any thoughts or suggestions? I have never taken images via a telescope so this is a whole new ...
97 views

### Is it possible to have a trinary star system with a planet that orbits their barycenter?

I am trying to model a 3-star system with a planet. The three stars have the same mass. I have gotten the stars (Yellow, Pink, Blue) into a stable orbit. However, I am wondering if a "free-...
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### How can something infinitely big have expanded from an infinitely small?

Please help me reconcile what I see as contradicting theories: The universe began with the Big Bang and expanded from an infinitesimally small point. The universe is infinite. How can something ...
138 views

### Is cosmology an accurate field? [closed]

I'm new here this is my first question. I'm an engineering student and I really like mathematics, I've recently watched a movie about Stephen Hawking (The Theory of Everything) In which he makes ...
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### At what distance could a supernova damage the Earth's ozone layer?

As from my latter question it seems Betelgeuse might be much closer than the usually presumed 640 light years. It might be as close as ~440 ly. Suppose it is, would this have any dangerous effects on ...