Recent content by cadnr

The EPOXI team is currently performing just such observations of the Earth, for use in exoplanet characterisation. They are using the Deep Impact spacecraft (originally used to make a close encounter with a comet), which is currently about 50 million miles from Earth. The measurements have...

The reference is to continuum emission at a particular wavelength. Imagine an emission continuum. It's quite possible to specify the flux at a given wavelength isn't it. For example, the continuum emission from a blue star is less at a red wavelength (say, 700 nm) than a blue wavelength (say...

Here are some tabulated rotational partition functions for various molecules: http://www.astro.uni-koeln.de/site/vorhersagen/catalog/partition_function.html The values are listed as log10(Q(T)) where Q(T) is the partition function at temperature T.

I suppose, however, that for sufficiently high energy collisions, the Pauli exclusion force might also come into play

Um, you might look up the Saha equation... that could be relevant

In this wavelength range, most of the radiation comes from the photosphere, which I don't think would vary much in size as a function of wavelength

I could be wrong, but maybe refractive index increases towards the red in a plasma.

During the collision, kinetic energy of the moving atoms is converted into excitation energy of an electron. if the excitation energy is above the threshold for ionisation, then the electron may be lost from the atom. You'd be right in thinking the coulomb interaction is responsible for...

Mass loss is due to radiation pressure (outward) overcoming gravitation (inward). In very massive stars, the gravity at the surface is weak and the radiation strong, so the matter gets blown away. As astrorob says, in AGB stars molecules form as the star pulsates. This is due to the...

1) Yes the moon is orbiting the Earth, but very slowly (it only goes around the Earth about 12 times a year), so it's true to say that the motion about the sun is the dominant factor in the Moon's motion in the solar system. In a similar way, the Sun's motion around the Galactic Centre is...

Because the Doppler effect depends on line-of-sight velocity, not angular velocity - think of the velocity vectors of the stars involved and you will see how this works.

The space between galaxies is believed to have been heated by the universe's first stars, which were huge and millions of times brighter than our Sun. It would still feel cold for a human out there because solid bodies radiate heat very rapidly. The density of gas is so low that it would not...

Without looking at specific minerals, the best you could calculate would be a mean number density. Oxygen and silicon are the most abundant elements in the Earth's crust, so silicate (SiO_3) might give you a reasonable starting point for a rough calculation.

The easiest way to measure the Sun's orbital velocity is to examine the motion of the Galactic centre relative to background stars on the far side of the Milky Way. See for example http://www.chron.com/content/interactive/space/astronomy/news/1999/ds/990602.html

Nobody really knew what the Milky Way was until the last hundred years, let alone that we orbit its centre. To know this requires precise measurements of the speeds and distances of stars throughout the Galaxy, again, possible only using technology from the last hundred years or so.