Answers to some Astronomical Questions
A collection of questions and answers which I've collected over
the years, in no particular order.
-
Will a nearby supernova kill
all life on Earth?
-
I worked up this response a few years ago; thanks to
David Palmer and Robert Spiker for their help in putting it together.
I've also tried to calculate
how frequently a star will explode
close enough to the Earth to be dangerous.
That document is in Postscript, I'm afraid; there are too many
equations for HTML or plain ASCII text.
- What is the evidence for
ice on the moon?
- There's information from the Lunar Prospector mission,
and from the Clementine spacecraft.
- What are some limitations on
distances derived from heliocentric parallax?
-
- How are supernovae classified?
- available in
HTML table format
(thanks to Jim Benet!),
or ASCII text format.
- Is there evidence for periodicity of
impact events on the Earth?
-
- What do we know about
Martian meteorites,
-
and how do we know it?
A very nice summary by James N. Head of the Lunar and Planetary Lab.
- Is it good for astronomers
not to fall from observing ladders?
-
A short rant in which I warn against the increasing distance of
professional astronomers from the acquisition of their data.
- Why aren't CCDs the answer to every
astronomical imaging application?
-
A comparison of some astronomical detectors by Brian Skiff.
Originally posted to sci.astro.amateur.
- Are quasars really at
distances indicated
by their redshifts?
- or The Redshift Controversy;
a discourse
by Bill Keel of the claim that (some) quasars aren't at distances
indicated by their redshifts. Originally posted to sci.astro.
- What is the format of
a simple 16-bit integer FITS file?
-
- What is the "dust" in space?
-
An essay on the evolution of dust in the ISM, by Amara Graps.
Originally posted to sci.astro.
Latest update: July 29, 2000.
- What sort of telescope should I buy as a Christmas present?
-
- What does a radio galaxy
look like?
-
A brief summary by Martin Hardcastle, originally posted
to sci.astro.research.
- Is it possible to detect
supernovae with neutrino experiments?
-
Alex Habig explains the process by which this might be possible,
in a note originally posted to VSNET.
- Does the Cassini spacecraft
present a significant health risk?
-
No, but please
do read Jeff Cuzzi's analysis, originally posted to
sci.astro on September 16, 1997.
-
What type of film is best for astrophotography?
-
Thanks to Michael Covington (I enjoy my copy of his book).
- Why are there rings around
the remnant of Supernova 1987A?
-
Read Phil Plait's fine description and find out.
- Why do astronomers measure
distances in parsecs?
-
My answer was originally posted to sci.astro on Jan 29, 1998.
- Why don't Moths and astronomy mix?
- To see why, read
a description of moth-related problems at the Apache Point
Observatory.
Or take a look at
this picture, taken in June 2003.
- What is the "L" class of stars?
-
From a sci.astro posting by Neill Reid.
- What is Dark Matter?
-
A brief answer from a posting to sci.space.science.
- What's the relationship between visual and
photoelectric/CCD magnitudes?
-
Arne Henden supplies a brief answer in this posting to VSNET.
- Why do astronomers think there
are supermassive black holes at the centers of some galaxies?
-
Martin Hardcastle explains, in a message originally posted to
sci.astro.
- What's the difference between GMT and UT and
all those other timescales?
-
Paul Schlyter explains, in a message originally posted to
sci.astro.fits.
- Are there any upcoming high-energy
space satellite missions? What about the "Swift" mission?
-
David Palmer gives a nice summary of the "Swift" mission,
scheduled for launch in 2003, which will detect GRBs and
locate them precisely.
- Where can I find information
about a particular star?
-
Brian Skiff provides a guide to some excellent on-line
resources (from a post to VSNET-chat, Sep 10, 2001).
But do read his warning in the next item ...
- Can you always trust
those giant astronomical databases?
-
Brian Skiff shows that sometimes, just occasionally, one
needs to take the results of a query with a grain of salt ....
- Some comments on astrometry
with recent all-sky surveys
-
Brian Skiff rates several of the all-sky surveys.
- How have astronomers mapped the sky at different wavelengths?
-
Ned Wright's
NGSS proposal has a very nice figure showing
a number of recent surveys, with their sensitivity
and wavelength.
- Why do some stars pulsate?
-
Toshihito Ishida outlines
the kappa mechanism briefly ,
from a message originally sent to vsnet-chat, May 19, 2000.
- Why are there tides?
-
My short answer , with pointers
to some more detailed explanations.
Originally mailed to a curious student, Oct 6, 2000.
- How do globular clusters stay spherical?
-
My short answer , which
points out the key is lack of dissipation in
stellar systems. Originally posted to sci.astro
on Dec 10, 2000.
- Is light from the distant universe scattered, or not?
-
Radiation from the CMB is,
but light from distant stars is not.
Originally posted to sci.astro
on Dec 10, 2000.
- Can we see Apollo hardware on the Moon?
-
The short answer is "no", but there are
some pictures taken from spacecraft
in orbit around the moon
which show evidence for the Apollo hardware.
Based in part on a posting to sci.astro by Alex Blackwell
of the University of Hawaii,
Jan 3, 2001.
- How can I figure out the appropriate exposure time for my
CCD astrophotos?
-
Try using
Michael's signal-to-noise calculator
- Which colleges and universities offer undergraduate programs
in astronomy?
-
Check out
Tom Balonek's compilation of undergrad programs in astronomy
- Why do the gas giant planets (Jupiter, Saturn, Uranus, Neptune)
emit more energy than they receive from the Sun?
-
Marshall Perrin of UC Berkeley posted a short answer to sci.astro
which includes some good references:
read Marshall's explanation
- Where can I find information on a particular star?
-
- Who invented the term "parsec"?
-
A discussion
appeared in sci.astro in April 2002.
The short answer is probably Herbert Hall Turner, in 1913.
- How many measurements does it take to determine an asteroid's period?
-
Kim Lang provides some good advice.
Originally posted to the Minor Planet Mailing List in Aug 2002.
- Why do AM radio stations fade out (or in) at night?
-
David Knisely explains it all.
Originally posted to sci.astro in January, 2003.
- What are the first results of the Microwave Anisotropy Probe (MAP) mission?
-
Ted Bunn gives a summary.
Originally posted to sci.astro.research in February, 2003.
- How faint a star can a person see?
-
Brian Skiff provides some information
Originally posted to sci.astro.amateur some years ago,
and then re-posted in vsnet-chat in February, 2003.
- What is "differential" photometry?
-
Arne Henden describes the
basic photometric techniques.
Originally posted to CCD-astrometry-photometry on Nov 6, 2003.
- What would happen if 10^(75) ergs were released in intergalactic space?
-
This was a particularly interesting question which came my
way as part of the
MadScientist Network .
You can read
the full question and my take on the answer,
though of course there are many, many other ways to analyze the situation.
- How can I avoid common
mistakes while doing astrometry?
-
This question came up on the
Minor Planet Mailing
List
and it seemed appropriate to save it here for future reference...
- How dangerous is a chunk of weapons-grade
uranium?
-
Originally posted to
the Bad Astronomy forums on Jan 25, 2007.
- Why doesn't dark matter accumulate
at the center of the Sun?
-
Originally posted to
the Bad Astronomy forums on Mar 3, 2007.
Another good source of information is
Phil Plait's Bad Astronomy page.
Last modified Mar 3, 2007
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