# All Questions

59 views

### coordinates in ICRF

The International Celestial Reference Frame (ICRF) is defined based on distant quasars and the origin is the barycentre of the Solar system. So, how can we measure the coordinates (\alpha, \delta) of ...
74 views

### why are solar telescopes built on lakes? the site differnece between a solar and an optical telescope

According to the wikipedia page big bear, water can cool the observatory. Big bear is in the southern California. It is better to build it on a cold high mountain with stable and clear atmosphere? ...
33 views

### How is the age of a star on the Henyey track calculated?

I was reading Stellar Evolution in Early Phases of Gravitational Contraction, by Chushiro Henyey, where he writes, If $L \propto R^{-\alpha}$ along the path, the age of a star from the time when ...
42 views

### Sunsets: Mars/Earth

I understand why our sky is blue and turns red when the sun sets or rises. I know why the sky on mars is red, but why does it turn blue during sunsets and rises? Shouldn't this actually not work due ...
120 views

### For how many bodies can there be a stable orbit with no very heavy central body?

The question is a bit vague, but let me explain: Take for example 2 bodies of the same mass. They can orbit around their centre of mass/gravity. Is something like this possible with multiple ...
44 views

### Types of Exoplanets

We discover vastly more exoplanets, that are gas giants that orbit their parent star very closely, than small terrestrial planets that are more distant to their sun. Could this be due to the methods ...
40 views

### Probability of finding life-supporting exoplanets

We've found over a thousand exoplanets by now, but how many of them could support life? What percentage of newly found planets are potentially life-harbouring? Or haven't we found any exoplanets that ...
142 views

### Why aren't secondary mirrors offset to get rid of diffraction spikes due to the support vanes?

Some kind of ellipsoidal shape mirror could reflect to a secondary mirror which is not in the way of the infalling light. Two advantages are immediately obvious. The primary mirror would not be partly ...
277 views

### Can the Milky Way be seen with the naked eye? Does this apply to any galaxy? If yes, then how and when?

I have seen different pictures in a different community to showcasing the Milky Way. I can never tell whether it's edited or it's the real picture. Actually, I can never see any galaxy as such by with ...
72 views

### Milky Way stellar number density : is the stated equation in this paper incorrect?

The paper is : http://www.astro.washington.edu/users/ivezic/Publications/tomographyI.pdf The equation is equation #23 in the paper. It's a model for the density of stars in the Milky Way's disk. It ...
276 views

### How can we tell the difference between matter and antimatter by observation in space?

I just was wondering and searching on the internet with little luck in the topic. On Antimatter Wiki they tell the observable universe is built up by matter. I read antimatter can be detected in ...
395 views

### Longest and shortest wavelength

What is the longest and what is the shortest wavelength of light? How fast would a light-emitting object have to recede in order to shift the frequency of light to increase the wavelength from the ...
40 views

### Attraction to barycenter

If an object was a distance from a planet away that equaled the distance from the object to a moon of the said planet, would it be drawn into the direction of the barycenter as it is the common center ...
65 views

### Globular cluster star density as a function of distance from the center

Context: I want to simulate globular clusters in a simple way, just to display the positions of stars. Assuming isotropy, what would be a reasonable model of the stellar number density as a function ...
213 views

### How would the solar system look in a Geocentric model?

If I fix the Earth as the center of the solar system, what would this look like? Are there any good images? How complex is this system?
149 views

### Is radiation from neutron stars delayed by time dilation?

I understand a neutron star to be the densest stuff that can exist without becoming a black hole, the densest thing which directly gives off radiation we can detect. At the event horizon of a black ...
85 views

Ok so I was reading about the Fermi paradox, assuming life will form and thrive where possible as soon as possible and there is a very probable chance many other earths formed would they have started ...
37 views

### Exoplanets and relativity [duplicate]

Ok, so I have read about how exoplanets are found using all sorts of genius methods. I also understand the further an obect in a telescope is the further into the past I am looking. So given that ...
167 views

### What supernova has created the iron currently found in Earth core?

Iron is generated by stars in a certain part of their life cycle. Earth contains a lot of iron inside, however it is clear that this iron could have not been generated in a star in close proximity. If ...
304 views

### What happens to galaxies when they die?

Stars explode when they die and blast heavy elements into space. Do galaxies do the same thing?
107 views

### Standardized “constellation” regions?

The current system of constellations is historical and has kind of arbitrary boundaries. This has a number of obvious downsides: Difficult to define boundaries need complex tables to express Each ...
29 views

### What is a typical value for core-to-star efficiency?

I was reading Unfolding the Laws of Star Formation: The Density Distribution of Molecular Clouds by Kainulainen et al., which discusses star formation rates and efficiencies. One variable used is ...
28 views

### Occurence of Venusian transits

As transits of Venus come in pairs each seperated by 8 years, wouldn't that imply an accurate ratio between earths and Venus' revolution period? I've found the ratio to be about 0.681. I presume one ...
198 views

### Where might a semi proficient amateur analyst participate in meaningful astronomical efforts

I am a retired engineer that has an ongoing interest in space efforts. In my youth I did work on the Apollo program but on propulsion and vehicle thermal control: not flight dynamics. I have ...
93 views

### Evidence that galaxies are made of billions of stars?

What is the evidence that galaxies are made of billions of stars? Even faint galaxies? Can spectral analysis distinguish galaxies from individual stars?
24 views

### If conjuncting planets are 1/3° apart (geocentric) at 15° elongation how low could the elongation at closest approach be?

Does anyone even have a rough idea? I don't know which pairs of planets can appear close for longer without changing elongation too slow like Mars does when behind the Sun.
329 views

### “Up” and “down” in Space [closed]

From my understanding, "up" and "down" in space is going towards (down) an object's gravitational pull or (up) which is going away from it. I get confused with this explanation, and I believe simply ...
128 views

### Finding Latitude and Longitude of a person or of where a picture was taken

this is my first post on the Astronomy stack exchange site. Please let me know how this question is based on y'all's generally accepted criteria for a good question as well as possible improvements. ...
191 views

### Has the sun become way brighter the last years?

Up to last year, I never got blinded by the sun in everyday situations (e.g. running towards it), at no time of the year I was. But since last christmas, it occured to me more often that I cannot ...
64 views

### Difference in redshift between 2 interacting galaxies

I have a galaxy 'A', say at redshift 1. Let's suppose this galaxy has no peculiar velocity. What would be the redshift of another galaxy 'B', that has a radial velocity of 500 km/s, relative to A? ...
1k views

### Which is more rare: Lunar eclipse or Solar eclipse?

Which is more rare: Lunar eclipse or Solar eclipse? Please explain why either one is more rare than the other. Thank you in advance for your inputs.
377 views

### Stars in the sky

Are the stars we can see with the naked eye in the night sky only from our Milky Way galaxy or can we see stars from Andromeda? I am aware we can see other celestial objects like nebulas and the ...
368 views

### Why can we see stars but not astronaut on the moon

A question came up today in astronomy class and it got me wondering all night. How is it that if stars are so far away, we can see them so clearly but we cannot see astronauts on the moon.
89 views

### Calculating the age of the universe

Is the calculated age of the universe that of the visible universe or the entire universe? I dont know how the age is calculated but if it is believed that all we see visibly IS the entire universe ...
445 views

### Mini black holes, a possible result of the LHC experiment at CERN

A scientist at CERN LHC (Large Hadron Collider) was asked during an interview about the possible results and consequences of operating the LHC at full power of collision in the near future, one of the ...
49 views

### Two body transient solution

In the two body problem, if each body is given an initial condition as a momentum vector, what is the transient part of the solution as it settles into the steady state orbit?
229 views

### Claim that 30-m class telescopes will have resolution far superior to Hubble: true?

This article makes the claim that the Giant Magellan Telescope (GMT, number 4 in the list) will have resolution 10 times better than that of Hubble, while the Thirty Meter Telescope (TMT, number 3 in ...
53 views

### Is it possible to get the distance to a star in the IPHAS DR2 catalog?

I'm looking at the IPHAS DR2 catalog. It has the Right Ascension and Declination but I'm not seeing any distance information (lightyears or parsecs). I'm wondering, given the columns in the dataset, ...
85 views

### What would this moving point of light be?

Tonight (10:00 PM EST Middlesex County, Mass.) when looking at the mostly clear sky I observed what I at first believed was a meteor. This point of light was moving east to northeast and that would be ...
262 views

### Why is the moon a fuzzy, white ball?

I currently own a telescope, I'm an amateur astronomer and currently just trying to view the moon. I own the Celestron PowerSeeker 70AZ. Link for information on the telescope: ...
93 views

### Cosmological deflation?

Wikipedia tells us: In physical cosmology, cosmic inflation, cosmological inflation, or just inflation is the exponential expansion of space in the early universe. The inflationary epoch lasted ...
211 views

### On a log-log plot of surface gravity to planet mass, what is the meaning of the y-intercept?

I am playing around with data from exoplanets.org, and am interested in the plot of surface gravity to planet mass. I reproduced this plot after downloading their data and performed a non-linear ...
313 views

### Why does the Solar System have no (natural) satellites of satellites?

What are the conditions for a planetary moon to have a satellite of its own? How far do the Solar System's bodies fall from the necessary threshold?
160 views

### What is the most populated/numerous stellar system in which the orbits of all objects are known?

I posed a question or two on here a couple months or so ago about the orbital patterns of each of the seven stars in the two septenary star systems Nu Scorpii and AR Cassiopeiae. They remain ...
156 views

### Is there a way to tell what the surface of a planet is like?

Kepler-442b I'm doing a project in which I need to find a planet within our galaxy that might be habitable. I found this planet that is within its stellar system's habitable zone, and due to research ...
101 views

### Would dark energy save the earth for a while as the sun heats up?

Would the expansion of space (e.g. dark energy) move the earth further away from the sun over time, possibly saving us for perhaps a few billion years as the sun heats up? Scientists now tend to ...
120 views

### Star versus Black Hole

I'm making a simplified animation for college project on how a star reacts with a black hole. I had known that a black hole sucks in everything and thus should be doing the same for stars. But upon my ...
99 views

### Could our Sun be a companion star of a massive black hole?

Can we track its orbit well now? There is any study that may indicate our sun may be a companion of a big black hole? What is the current constrain about its orbit now? There is a 1000 solar mass ...