# All Questions

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61 views

### Dark matter and vacuum

How different would space have been if there was no dark matter? Can space be considered vacuum even when occupied with abundant dark matter?
100 views

### Why pulsar pulses are so extremely regular?

It's often said that the pulses of the pulsar have a very precise period, which helps to detect easily exoplanets that cause fluctuations in the time of arrival (TOA) of the pulses. Anybody knows why?
39 views

### I also see the line of 30 stars @today(11/jan/2020)on5:35am [duplicate]

I can't take any pic because I don't know how many light are coming.
16 views

### How to search binaries in Simbad using spectral types

In the Simbad database there are many binary stars listed with the spectral classification of each component. For example, for $\alpha$ Centauri, Simbad yields a spectral type of G2V+K1V. My question ...
20 views

### INDI protocol with AZ GoTo SynScan to control an amateur telescope mount : problem with tracking

I have a SkyWatcher telescope with an AZ mount and a SynScan GoTo to drive the telescope. I want to drive the telescope from my computer. Using Linux, I use the INDI protocol (https://www.indilib.org)...
25 views

### How is length of meridian calculated in 1793?

I was studying metrology and came across it. Kindly help me with this query? In 1793 the length of meter was realized using the length of the meridian passing through Paris divided by 10 raised to 7....
53 views

### more than 30 moving stars [duplicate]

I am Abdul Kadhir from Kochi, Kerala, India. I, my wife and my daughter have seen today (2020-01-11) morning 5.45 AM IST a line of stars. A pair of more than 30 stars moving in a line from south to ...
91 views

### Is there a verification of the solar system barycenter as it is theoretically determined?

The barycenter of our solar system is not the sun, but a changeable location outside of the center point of the sun. A often used diagram of that relation is shown below, originated from the Wikipedia ...
142 views

### What is the cycle for when the maximum amount of the Moon's apparent area is sunlit?

The Moon is defined as full when its ecliptic longitude is 180$^{\circ}$ distant from the Sun's. But what is the cycle for when the maximum proportion of the moon's apparent area is sunlit, and for ...
41 views

### Approximately how many light years across (arclength) was the furthest reaches of the Hubble Ultra Deep Field?

I can find the area($11^2$ arcminutes) and lengths ($200$ arcseconds per side) but if I were to consider just the furthest region (arclength) of the survey, about how many light years across would ...
35 views

### Metal lines in Lyman-alpha forest

I need to find metal lines in the Lyman-alpha forest of quasar spectra, without the red side of lyman alpha emission line. Can you guide me how to do this?
109 views

### Does mean solar time and sidereal time sometimes indicate the same time?

I'm trying to wrap my head around the different definitions of time. Since mean solar time depends on the Sun, and sidereal time depends on the stars, and since the position of the Sun relative to the ...
48 views

### How are small objects automatically identified and their locations determined in digital images?

I have a large quantity of old digital images of low energy electron diffraction (LEED) patterns that I must process to identify and locate small, sometimes elongated gaussian-like blobs of a few ...
124 views

### Exposure details for this now (in)famous image from Lowell Observatory?

IAU's announcement 19035 IAU Statement on Satellite Constellations, 03 June 2019 links to 19035a Trails made by Starlink satellites which contains the image shown below. Question: Is it possible to ...
71 views

### Could the mineral composition of planets explain the absence of megastructures?

The Fermi paradox concerns why we don't observe evidence of alien life, such as megastructures. If we were to build a Dyson swarm, the best source material may be Mercury (Armstrong and Sandberg 2013):...
66 views

### What is the LSST now?

Space.com's It's Official: Vera Rubin Observatory Named to Honor Dark Matter Scientist says: "We're here today to focus on the major renaming of the facility after a pioneering astronomer, that is ...
57 views

### How much higher is the radiation around Jupiter than at Chernobyl, after the explosion?

I suppose the radiation levels are higher at Jupiter, but how much? Would the Juno probe have been able to "operate" on the Chernobyl roof in 12000 roentgen/hr? After watching the short series ...
42 views

### Verifying refractor lens about scratches

I found an used Skywatcher 70mm telescope for buying, but its lenses are a little suspect about harming. In one photo, it looks clearly a scratch, but in the another, it is not visible. Could it be an ...
104 views

### Is there a stellar database that indicates how long ago stars in our Galaxy formed?

There are several ways of determining the age of a star: its position in the HR diagram, the presence of a protoplanetary disk, it belonging to a cluster... When did the stars in our Galaxy form? Do ...
72 views

### What constellation is closest to the Zenith with RA=12 and Dec =47.6?

I have several options, but I do not know how to calculate which option is closest to the zenith in title. Could you please help me with this? Thank you. ...
68 views

### Age of earth relative to other planets

Relative to the average age of other known planets, is the earth young, old or in the middle? Does it make a difference if you compare the earth against nearby planets (say < 500 LY), or other ...
54 views

### Catching up with Hubble domain galaxy at constant acceleration: is it possible? If yes, what time will it be when I arrive?

An elf gave me a magic spaceship for Christmas: it can maintain a thrust of $\alpha = 10\ \mathrm{N/kg}$ indefinitely. Otherwise, I'm still constrained by physics. I plan to set out on a journey into ...
39 views

### Primordial black holes microlensing

Could the movement of a PBH found in the outer solar system by microlensing be totally unpredictable and impossible to track after it was first detected?
69 views

### In the milky way which star(s) are farthest from galactic plane?

I am looking for at least one star on each of the side of the galactic plane. I understand there would be an error tolerance. So, please do not hesitate if the answer is not exact. Preferably, please ...
54 views

### Orbitally convenient Mars-to-Earth transit times?

Are there any peculiar solar system layouts that would result in highly efficient transits between Mars-to-Earth? I am aware of a Hohmann transfer orbit, but can other planets be used to "sling-shot" ...
116 views

### Does a flat universe mean not finite and circular?

I am trying to wrap my head around what a flat universe means; Trying to imagine why angles of triangles in spherical volumes are different. Because my brain can't do that well and I became a bit ...
67 views

### Why is constant velocity drift not an accepted explanation of Hubble expansion?

Edward A Milne at the Oxford University proposed that what Hubble was observing was simply a natural sorting of random galactic motions. If a group of galaxies formed together moving at various ...
67 views

### Does a black hole necessarily contain a singularity?

I'm basing this hypothesis on the theories around how an outside observer watching something fall into a black hole will never actually see the thing pass the event horizon. And secondly that from the ...
34 views

### how to calculate the half-mass radius and tidal radius of a (simulated) globular cluster

I am exploring a dataset of a direct N-body simulation of a star cluster, such that all particles have the same mass and G = M = −4E = 1 for the whole cluster. The data available is the positions ...
115 views

### Where can I find Helium 3 in our solar system?

What are the best locations within the solar system to find Helium 3 excluding the Sun? Where is Helium 3 most abundant after the Sun?
66 views

### DSO in a 60mm telescope

I am thinking about buying a telescope, but here in Brazil they are very expensive and hard to find where to buy. So, the better telescope I can pay for is a Celestron Powerseeker 60AZ. My main ...
17 views

### X-rays, Solar wind and Sun's corona

I was reading that Solar corona emits the solar wind however also X-rays. What is the difference during the creation of these effects and impacts on our atmosphere? Thank you!
221 views

### How Will Starlink Affect Observational Astronomy?

I have recently found that people around the world have been posting observations of a line of moving objects in the sky which is very likely to be a part of Starlink satellite constellation, such ...
37 views

### Actual meteor sightings formula

I'm trying to realistically approximate the value of meteor sightings during a meteor shower because I don't want to have high expectations going in. I have a couple questions about this formula I ...
28 views

### Calculating angle between the sun and a perpendicular to earth given lon/lat & time

If you had your longitude/latitude, and the time/date, how could I go about working out the angle between your normal and the sun? At first I was doing a simplistic approach of assuming elliptical ...
114 views

### Plotting Astronomical Data Using Python

I have been trying to create a graph which shows the distances between the stars and the earth, yet I could not obtain the desired graph as seen below (click to zoom in): My graph: As @uhoh ...
70 views

### Derivation of the orbital parameters of a exoplanet discovered by direct imaging

I wonder which orbital elements of a exoplanet can be found only applying direct imaging. I know that the angular separation combined with parallax can give us the semi-major axis, but what about the ...
249 views

### How can a singularity actually exist?

Probably a stupid question, but it "bothers" me and I can't find a concrete answer on the internets. When you fall into a black hole, afaik, time slows down for the matter falling in as it gets ...
140 views

### Quadrantids Meteor Shower 2020 viewing times

It's my first time going to see the Quadrantids Meteor Shower, or any meteor shower in fact. I just want to know if I'm getting the right info for viewing this event. I got my info from this site ...
54 views

### stars moving in the sky or something [duplicate]

I was out in the garden having a cigarette and was watching the shy looking at three stars for about 5 minutes. suddenly they moved in the sky and crossed paths.one has now stopped still and would ...
73 views

### How can I calculate 27 tropical/solar year since my birthdate?

Let's say I was born on 27th November 1993 at 03:15:15 AM. Is there any way I can calculate exact 27 tropical cycle since my birthdate/birthtime. What date and what time it will be after exact 27 ...
38 views

### Astronomical events and Celebrations

In the past people celebrated important astronomical events and some of those events are still celebrated in some cultures and traditions. For example: March/September equinox, New Moon, Winter/...
428 views

### Why do the upper-atmosphere clouds of Venus appear to have that V shape?

IF I understand correctly, the atmosphere moves in the same direction as the rotational spin, but about 60 times faster. It is driven from the hot side of Venus to the cold side (the difference being ...
35 views

### For any given meteor shower in a given year (e.g. Quadrantids, now) where can I see a rough prediction of how many days it will last?

For a given shower the rate hitting the Earth's atmosphere versus time is usually a peak with a width of a few days, though there are some exceptional unicors. Is there a place where I can view this ...
41 views

### Could the impresssion of a accelerated expansion of the universe come from a loss of energy of light on a large scale of time?

How do we know that redshift is not the result of energy loss or wave expansion of light on a large scale of millions of years that we have never been able to observe? How can we exclude the ...
34 views

### Identifying consecutive flying objects [duplicate]

First of all, sorry for my complete lack of knowledge in the field! The event I'm describing left me puzzled and I'm looking for possible explanations, and I thought I'd start here. I saw a number of ...
2k views

### Are stars expected to become dimmer before a supernova?

With the recent news about the "fainting" of Betelgeuse and the speculation that this might be a precursor to a supernova, I'm wondering if there is any theoretical/observational basis for this ...
39 views

### Name of extra-terrestrial “moon's” orbital period? [duplicate]

Is there a commonly used alternative to "month"? Or does that work for any moon?