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No, Pluto is a so called resonant trans-neptunian object; the orbital period of Pluto is almost exactly 3:2 (1.5) times that of Neptune. This means that every time Pluto nears perihelion and is ...

Actually, the stars and nebulae that make up the spiral arm are only temporarily part of that spiral arm. Spiral arms are more like sound waves where individual particles move around a more or less ...

Depends on the interpretation of your question... The best places not to observe the moon are the north and south pole. On the north pole you will only be able to see objects above the celestial ...

Most stars form in clusters, so it is very likely that the Sun was part of a star cluster when it formed. But in On the Dynamics of Open Clusters, the relaxation time of a cluster is calculated to ...

Certainly. Astronomical Unit is probably one of the most used distance units used in astronomy. It is of course only used when discussing the distances within a stellar system, such as the distances ...

You can calculate the angular diameter of the Earth using the equation: $$a = \arctan \frac{D}{d}$$ where $a$ is the angular diameter, $D$ is the physical diameter of the Earth, and $d$ is the ...

This can only happen if the moonrise at a certain date is earlier than the moonrise at the previous day. There are two reasons why this could happen: The body (Moon, Mars,...) moves in the opposite ...

It depends a bit on how precise you would want to be. A very good discussion on how to calculate the orbits of solar system objects is given in the book by Jean Meeus, Astronomical Algorithms (1999), ...

The apparent magnitude (in V ~ visual) is in column 42-46. Other magnitudes are BT magnitude (columns 218-223) and VT magnitude (columns 231-236). These are magnitudes recorded with different (colour) ...

Yes there is a difference, Kuiper Belt Objects (KBOs) are a subset of Trans Neptunian Objects (TNOs). Other subsets are Oort-cloud objects (OCOs) and scattered disk objects (SDOs). These are not KBOs ...

VY Canis Majoris and UY Scuti are variable star designations. The first discovered variable star in a constellation is called R, the second, S, and then unto Z. After Z comes RR and so on. For a full ...

Given the angular diameter $a$ in radians and the distance $d$ in Mpc, you can get the actual diameter $D$ from: $$D = d\tan{a}$$ Using the small angle approximation, you get: $$D = da$$ $a$ is in ...

The classification of stars using spectral class is a very useful classification when considering the properties of (the atmosphere of) a star at that moment. If you consider the different stages in ...

No it does not have the same composition everywhere. In the core hydrogen is fused into helium, so the fraction of hydrogen (denoted by $X$, between 0 and 1) decreases while the fraction of helium ($Y$...

Depends on what you would call noticeable. The perturbations between the planets are quite small and you will only notice them if you either measure the positions of the planets very accurately or ...

Yes, you are correct. The luminosities can be added. Luminosity is the amount of electromagnetic energy emitted per unit of time (measured in $\textrm{J} \cdot \textrm{s}^{-1}$ or $\textrm{W}$). So ...

Due to the atmospheric refraction the Sun rises earlier and sets later as you correctly wrote. Refraction however is perpendicular to the horizon. So if the apparent sun rise is earlier, than the true ...

The beginning of the year (1st of January) has been chosen for historical reasons (near the winter solstice) and has absolutely nothing to do with Earth's perihelion passage. Earth's perihelion could ...

Potentially photons emitted by your torch could travel to infinite distances, assuming the universe will keep on expanding. If the light gets further away, the photons of your torch will be spread out ...

The most accurate system is the ephemeris service from Jet Propulsion Laboratory (JPL): http://ssd.jpl.nasa.gov/horizons.cgi

Actually the method described on Wikipedia is not the method that is meant by Spectroscopic Parallax. To determine the spectroscopic parallax, you'll need a spectrum of the star and measure the widths ...

1) this question has no real answer as it depends on the reference frame being used. It is very unlikely that they will be stationary except in their own reference frame. rephrased 1) In theory ...

Is there any standard software or algorithm for computing the Sérsic index from an image? I don't think it is standard but Vika et al (2013) have used a modified version of GALFIT to extract Sérsic ...

If I understand your question correctly than your problem is that the primary direction of vCR[3] is the intersection between the prime meridian and the Earth's equator, instead of the vernal equinox. ...

The European Southern Observatory has catalogues with image data available from http://www.eso.org/qi/, you will have to register before you are able to access them. I'd suggest you look at other ...

As @barrycarter mentioned you can use the Horizons web interface from JPL: http://ssd.jpl.nasa.gov/horizons.cgi You can change the setting in the web form by clicking on the [change] links for the ...

Most of the stars in the Hipparcos catalogue do not have a common name. In the main catalogue file you will also find the Henry Draper (HD) number of the star (if it has one) at columns 391-396. You ...

There is actually disagreement on this matter (within the IAU?). Dr. Alan Stern (lead of the New Horizons mission) for instance points out that "this rule is inconsistent" (e.g. see Pluto vote '...