The science dealing with objects and phenomena located beyond Earth. In particular, this applies to observations and data. At its core, astronomy is the physically informed cataloging and classifying of the contents of the universe in order to better understand what is out there.

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11
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4answers
7k views

What does f/4.6 mean in a telescope and how important is this value? [closed]

In some specifications for telescopes, I saw a value marked as f/4.6. What does it mean exactly, and how important is when it comes to choosing a telescope?
8
votes
1answer
143 views

Best periods to observe Magellanic Clouds?

When is the best period of the year to observe the LMC and SMC in the Southern hemisphere, so that I can observe them at a reasonable time (e.g. around 10 in the evening?). I am in Sydney.
0
votes
2answers
191 views

Gyrochronology, the formula is empirical ?

The formula used in Gyrochronology that relates a star's Period of Rotation-Mass-Age is empirical? This news How to Learn a Star’s True Age "“A star’s rotation slows down steadily with time, ...
2
votes
3answers
221 views

What is the strange event in this simulation of a galactic collision?

I was watching this video on YouTube: 2 Spiral Galaxies w/Supermassive Black Holes Collide Around half way, and again almost at the end, the black holes seem to suddenly give off some sort of force ...
4
votes
2answers
143 views

What really are some distant astronomical bodies that seems like dust clouds?

Looking at pictures like this I bet it is a picture of a giant cloud of dust, bigger than a galaxy and made of asteroids and planets (instead of stars). But probably I'm wrong. What is that?
2
votes
1answer
547 views

IRIS alternative on mac?

I need to process some images taken from a telescope to determine the intensity of an astroid. This way I can determine the rotation period of this asteroid. The pictures were taken the usual way ...
3
votes
2answers
4k views

Glycerol: refractive index & absorption spectra in 0.2-0.4um range

Could anyone suggest where can I find absorption spectra & refractive index of Glycerol? I am specifically interested in UV range, 200-400nm, everything I was able to find out was for standard ...
0
votes
1answer
174 views

What is 656 Beagle?

What kind of object is 656 Beagle (1908BU)? I know it's a minor planet, but that includes a large array of different stuff. Specifically, I am looking at the general chemistry/geology of the object.
2
votes
2answers
862 views

What is meant by positive and negative gravity/energy/spactimecurvature?

I have recently come across some cosmological assertions (based on empirical data) about the universe being self contained in the sense that it is entirely capable of coming into existence from a ...
7
votes
3answers
472 views

Are there planetary systems where the planes of orbits vary greatly?

Inspired by this question, are there any known planetary systems with largely varying planes of orbit? For example a system where two planets have perpendicular planes?
5
votes
1answer
156 views

Oort Cloud Detection

The hypothetical Oort cloud is an explaination for long period comets. It presumably is made up of icy bodies orbiting up to 50,000 AU from the Sun. If so, shouldn't the Spitzer IR telescope have ...
1
vote
0answers
224 views

Is the conclusion that the cosmic burst observed in the Draco constellation from gamma rays that are streaming towards a massive black hole correct?

Referencing this news article: http://www.smh.com.au/technology/sci-tech/cosmic-burst-in-far-away-galaxy-puzzles-nasa-20110408-1d6kz.html It also references an event id: (GRB) 110328A The article ...
2
votes
1answer
125 views

Solar Cycle UV Variation

The average energy we receive from the Sun is 1,366 w/m^2, and this only varies by 0.1% from the activity peak to trough of its 11 year cycle. About 9% of the energy comes from wavelengths less than ...
-2
votes
5answers
283 views

Does the rotational speed of a planet consistently become faster and faster given that there are no conflicting events? [closed]

Does the rotational speed of a planet consistently become faster and faster given that there are no conflicting events?
4
votes
1answer
1k views

Gravity and Planetary Differentiation

During solar system formation, many bodies achieved hydrostatic equilibrium, a spherical shape where their self gravitational force was balanced by internal pressure. Many also achieved ...
11
votes
4answers
5k views

Why does Venus rotate the opposite direction as other planets?

Given: Law of Conservation of Angular Momentum. Reverse spinning with dense atmosphere (92 times > Earth & CO2 dominant sulphur based). Surface same degree of aging all over. Hypothetical large ...
7
votes
1answer
224 views

Mass Needed to Clear an Orbital Neighborhood

In 2006 the IAU deemed that Pluto was no longer a planet because it fails to "clear" the neighborhood around its Kuiper Belt orbit. Presumably, this is because Pluto (1.305E22 kg) has insufficient ...
5
votes
2answers
306 views

Does the math work out for there being enough time for the formation of the heavier elements and their distribution as seen in today's universe?

Currently accepted scientific theory says that all elements heavier than hydrogen, helium, and a little lithium have been created in supernova explosions. My questions, specifically, is has anyone ...
1
vote
4answers
8k views

How does the moon reflect light?

We can see the moon in the night because it reflects sunlight. But the light is incident on the opposite side of moon with respect to the observer in the night. In this case, how does the moon ...
6
votes
3answers
854 views

Why does the light side of the moon appear not to line up correctly with the evening sun?

I live at roughly 52.4,-2.1. On a sunny evenings I've often looked at the moon and the sun and noticed that the light part of the moon does not appear to line up with the sun. For example, at about ...
2
votes
2answers
213 views

The size of the planets

What calculations were done to discover the size of all the planets?
3
votes
1answer
2k views

Find true anomaly given period, eccentricity and time

Is it possible to find the true anomaly of an object in a Kepler orbit given the orbital period of the object, the orbital eccentricity and the time? Assuming a two body system and the mass of the ...
3
votes
1answer
448 views

Does the long axis of Earth's orbit precess? Does it nutate?

Get up off the plane of the ecliptic by a couple of million miles. Look back at the Sun and watch the Earth's orbit in time-lapse for a few centuries. The orbit is an ellipse tilted at 23.5 degrees ...
0
votes
3answers
112 views

Is there a chance for Earth to have an additional satellite someday?

I am just an space enthusiast and not a physics professional so pardon me if this is not the right place to ask. As title says, is there a chance for our Earth to have additional satellite(s) like our ...
11
votes
1answer
285 views

Why are all-Sky images drawn as a filled ellipse?

There is some convention? how is this 3d to 2d mapping done? here an example
4
votes
1answer
192 views

Gamma Ray Bubble at the center of our galaxy seen by Fermi Telescope

How could we measure high energy photons, whithout measuring them ? I can't understand how we can "see" those Gamma Ray Bubbles if they are not reaching here In this graph from Nasa you can see ...
2
votes
1answer
522 views

Astronomical detection significance from magnitude error

At this website: http://heasarc.gsfc.nasa.gov/docs/swift/analysis/threads/uvot_thread_afterglows.html The passage at the bottom states that a V-band magnitude of 17.62, with an error $\pm$0.02 is a ...
1
vote
4answers
228 views

Astronomy: Are any vanished objects visible to the naked eye?

Are there any objects out there that have since vanished, but because of their distance and the travel time for light, can be seen with the naked eye? Or are those things only visible with ...
2
votes
3answers
202 views

Is the “far” universe expanding more quickly?

I'm reading this silly Time article: http://www.time.com/time/health/article/0,8599,2044517,00.html And they say "Even at its best, the 20-year-old telescope never had the acuity to peer so far into ...
3
votes
2answers
11k views

How is the speed of light calculated?

How is the speed of light calculated? My knowledge of physics is limited to how much I studied till high school. One way that comes to my mind is: if we throw light from one point to another (of known ...
9
votes
2answers
15k views

How is distance between sun and earth calculated?

How has the distance between sun and earth been calculated? Also what is the size of the sun?
-2
votes
1answer
526 views

History of Man Acquired knowledge of solar system [closed]

I know the basics of solar system like how earth moves around sun, and that we have so many planets, elliptical orbit of earth, and how far is sun from earth etc etc. I want to take a step back and ...
2
votes
3answers
142 views

Planetary Atmospheres

Venus (0.815 Earth mass) supports a CO2 atmosphere of 93 bars at its surface. Earth's N2/O2 atmosphere has a surface pressure of one bar. What are the factors that limit the mass of atmospheric gases ...
2
votes
1answer
276 views

What happend with the light from all the galaxies visibles from an earth telescope?

Supposing it's possible to see some distant galaxies with an earth telescope, then, at the tip of the telescope lens there are photons comming from the distant galaxy... So, if I extend my hand in a ...
3
votes
3answers
2k views

Why do stars have absorption spectra?

Absorption spectra are a result of light of a certain wavelength exciting an atom from a lower energy level to a higher one and at the same time being absorbed. However, the atom should eventually go ...
7
votes
6answers
9k views

How fast is Earth moving through the universe?

As the galaxy is moving and the solar system orbiting the galaxy and the Earth orbiting the sun. So how fast is each object moving and what is the fastest we move at? Do we even know how fast the ...
1
vote
1answer
361 views

How is the mass of black hole at the center of our galaxy measured?

I've been watching a video about dark mater and a lot of the mass is missing in our universe. Astronomers got to this by measuring the speed that stars orbit the center of the galaxy and when they did ...
5
votes
4answers
861 views

Optical explanation of images of stars?

Very often when viewing pictures of the cosmos taken by telescopes, one can observe that larger/brighter stars do not appear precisely as points/circles on the image. Indeed, the brighter the light ...
6
votes
3answers
334 views

How accurately is the moment of perihelion of Earth known, and how is it measured?

Earth's perihelion passed about nine hours ago. How accurately do we know the moment of closest approach of the Earth to the center of the sun? How do we make this measurement?
19
votes
6answers
4k views

Why are the orbits of planets in the Solar System nearly circular?

Except for Mercury, the planets in the Solar System have very small eccentricities. Is this property special to the Solar System? Wikipedia states: Most exoplanets with orbital periods of 20 ...
1
vote
1answer
192 views

Astrophysical Data

I am working on a project that requires some amount of number crunching. I require some basic data about the galaxy M82 and our own Milky Way (particularly luminosities). My advisor is a nut and he ...
2
votes
0answers
322 views

What is the name of the physical space enveloping all universes? [closed]

Please excuse my question, as i don't come from a physics background, but i was really wondering. Assuming we are in one of numerous universes which all have physical dimensions: What is the name of ...
4
votes
1answer
347 views

Exoplanet surface detail: Limitations on size of space telescope array

How big could an array of space telescopes acting as an interferometer be ? How big would it have to be to resolve exoplanet surface detail the size of Iceland at a distance of 100 light years ?
4
votes
1answer
347 views

Lunar twilight and sixth magnitude stars

Summary: when the Moon is x degrees below the horizon, it interferes with stargazing the same as astronomical twilight would. What is x (as a function of the Moon's phase)? We define civil, ...
30
votes
8answers
21k views

Why CAN we see the new moon at night?

I understand that the Moon's phases are determined by its position in orbit relative to the Sun. (See: Full Story on the Moon). The "shadow" is not cast by the Earth (a common misconception - this is ...
14
votes
6answers
5k views

Why is the mapped universe shaped like an hourglass?

I've watched a video from the American National History Museum entitled The Known Universe. The video shows a continuous animation zooming out from earth to the entire known universe. It claims to ...
11
votes
3answers
484 views

If time standard clocks and any memories about the time standard are destroyed, can we recover the time standard again?

Assume the time standard clocks and any memories about the time standard are destroyed. Can we recover the time standard again exactly? Recovering the time standard again means we can determine the ...
7
votes
6answers
2k views

Is rotational motion relative to space?

Let's assume that there is nothing in the universe except Earth. If the Earth rotates on its axis as it does, then would we experience the effects of rotational motion like centrifugal force and ...
5
votes
3answers
986 views

How would I calculate celestial body characteristics without a priori knowledge?

Without any a priori knowledge of the mass, speed, distance, and size of local celestial bodies (aside from Earth's size), what can I calculate and how from my "backyard" through observation? Edit: ...
9
votes
5answers
3k views

What methods can astronomers use to find a black hole?

How can astronomers say, we know there are black holes at the centre of each galaxy? What methods of indirect detection are there to know where and how big a black hole is?