Last-modified: $Date: 1996/10/12 00:39:42 $
Version: $Revision: 2.0 $
URL: http://astrosun.tn.cornell.edu/students/lazio/sci.astro.html
Posting-frequency: semi-monthly (Wednesday)
Archive-name: astronomy/faq/part2

------------------------------

Subject: Introduction
 
 sci.astro is a newsgroup devoted to the discussion of the science of
astronomy.  As such its content ranges from the Earth to the farthest
reaches of the Universe.
 
 However, certain questions tend to appear fairly regularly.  This
document attempts to summarize answers to these questions.
 
 This document is posted on the first and third Wednesdays of each
month to the newsgroup sci.astro.  It is also available via anonymous
ftp in the directory <URL:ftp://seti.tn.cornell.edu/pub/lazio/> and it
is on the World Wide Web at
<URL:http://astrosun.tn.cornell.edu/students/lazio/sci.astro.html>.
 
Questions/comments/flames should be directed to the FAQ maintainer,
Joseph Lazio (lazio@spacenet.tn.cornell.edu).
 
------------------------------

Subject: Copyright
 
 This document, as a collection, is Copyright 1995,1996 by T. Joseph
W. Lazio (lazio@spacenet.tn.cornell.edu).  The individual articles are
copyright by the individual authors listed.  All rights are reserved.
Permission to use, copy and distribute this unmodified document by any
means and for any purpose EXCEPT PROFIT PURPOSES is hereby granted,
provided that both the above Copyright notice and this permission
notice appear in all copies of the FAQ itself.  Reproducing this FAQ
by any means, included, but not limited to, printing, copying existing
prints, publishing by electronic or other means, implies full
agreement to the above non-profit-use clause, unless upon prior
written permission of the authors.
 
 This FAQ is provided by the authors "as is," with all its faults.
Any express or implied warranties, including, but not limited to, any
implied warranties of merchantability, accuracy, or fitness for any
particular purpose, are disclaimed.  If you use the information in
this document, in any way, you do so at your own risk.

------------------------------

Subject: B.00 General

[Dates in brackets are last edit.]

    B.01 What are the largest telescopes? [96-06-14]
    B.02 What new telescopes/instruments are being built? [96-10-11]
    B.03 What is the resolution of a telescope? [95-08-23]
    B.04 What's the difference between astronomy and 
         astrology? [95-08-23]
    B.05 Is there scientific evidence for/against 
         astrology? [95-08-23]
    B.06 What about God and the creation? [95-08-27]
    B.07 What kind of telescope should I buy? [96-10-11]
    B.08 What are the possessive adjectives for the 
         planets? [95-12-05]
    B.09 Are the planets associated with days of the week? [96-05-29]
    B.10 Why does the Moon look so big when it's near the 
         horizon? [95-10-05]
    B.11 Is it O.K. to look at the Sun or solar eclipses using
         exposed film? CDs? [95-10-08]
    B.12 Can stars be seen in the daytime from the bottom of a tall
         chimney, a deep well, or deep mine shaft? [96-06-14]
    B.13 Why do eggs balance on the equinox? [96-06-14]
    B.14 How do I become an astronomer?  What school should I 
         attend? [96-07-03]

------------------------------

Subject: B.01 What are the largest telescopes?
Author: Bill Arnett <billa@znet.com>,
	William Keel <keel@bildad.astr.ua.edu>,
        Joseph Lazio <lazio@spacenet.tn.cornell.edu>,
	Steve Willner <swillner@cfa.harvard.edu>


Corrections and/or additions to these lists are welcome!

(Optical telescopes, nighttime)

The list below gives the largest optical telescopes operating today.
For complicated pupil shapes, the effective aperture diameter is
given.  Location is geographic; we omit most organizational details,
amusing and intricate as they may be.  The list stops above 2.1
because there are a lot of these scattered about.  URL's are given
where known.

Aperture  Name              Location 
10.0      Keck I            Mauna Kea, Hawaii
   (mirror composed of 36 segments)
   http://astro.caltech.edu/observatories/keck.html
   http://www.keck.hawaii.edu:8080/
   gopher://doulos.ucsc.edu/11/observe/maunakea (not much there either!)
 6.0      BTA               Nizhny Arkhyz, Russia
   (Bolshoi Teleskop Azimutalnyi = Large Altazimuth Telescope)
 5.0      Hale              Palomar Mountain, California
   http://astro.caltech.edu/observatories/palomar/
 4.5      Multiple Mirror   Mt. Hopkins, Arizona
   (6 mirrors, 1.8 m each; see also B.02)
   http://sculptor.as.arizona.edu/foltz/www/mmt.html
 4.2  William Herschel      La Palma, Canary Islands
   http://ing.iac.es/WHT.html
 4.0  Victor Blanco	    Cerro Tololo, Chile
   http://www.ctio.noao.edu/4m/base4m.html
 3.9  Anglo-Australian      Siding Spring, Australia
   http://www.aao.gov.au/
 3.8  Mayall                Kitt Peak, Arizona
   http://www.noao.edu/kpno/kpno.html
 3.8  UK Infrared           Mauna Kea, Hawaii
   http://www.jach.hawaii.edu/UKIRT/home.html
 3.6  ESO                   Cerro La Silla, Chile
   http://lw10.ls.eso.org/lasilla/lasilla-homepage.html
 3.6  Canada-France-Hawaii  Mauna Kea, Hawaii
   http://www.cfht.hawaii.edu/
 3.6  New Technology        Cerro La Silla, Chile
   http://www.eso.org/NTT/
 3.5  MPI-CAHA              Calar Alto, Spain
   http://www.mpia-hd.mpg.de/CAHA/
 3.5  ARC                   Apache Point, New Mexico (mostly remote control)
   http://www.apo.nmsu.edu/
 3.5  WIYN                  Kitt Peak, Arizona
   http://www.noao.edu/wiyn/wiyn.html
 3.5  Starfire		    Kirtland AFB, New Mexico
   http://www.plk.af.mil/PLhome/PA/FACTSHEETS/metertel.html
 3.0  Shane                 Mount Hamilton, California
   http://cgi.irving.org/cgi-bin/irving-cgi-bin/xplore.pl?lick+shnentry+A+M
 3.0  NASA IRTF             Mauna Kea, Hawaii
   http://irtf.ifa.hawaii.edu/
 2.7  Harlan Smith          Mt. Locke, Texas
   http://vulcan.as.utexas.edu/vc/vc_home.html
 2.7  Liquid Mirror         Malcolm Knapp Research Forest, British Columbia
   (mercury mirror)
   http://www.geop.ubc.ca/~cabanac/limits.html
 2.6  Shajn                 Byurakan, Armenia
 2.6  Crimean               Crimea, Ukraine
 2.5  Hooker                Mt. Wilson, California
   http://www.mtwilson.edu/
 2.5  Isaac Newton          La Palma, Canary Islands
   http://ing.iac.es/welcome.html
 2.5  duPont		    Las Campanas, Chile
   http://www.astro.princeton.edu/~ogle/warsaw/lco.html
 2.5  Nordic Optical        La Palma, Canary Islands
   http://www.not.iac.es/
 2.4  Hiltner               Kitt Peak, Arizona
   http://www.astro.lsa.umich.edu/obs/mdm/
 2.4  Hubble                Low Earth orbit
   http://www.stsci.edu/
 2.3  WIRO                  Jelm Mtn., Wyoming
   http://www.noao.edu/kpno/kpno.html
 2.3  Steward Obs.	    Kitt Peak, Arizona
   (to be renamed in honor of Bart Bok in 1996 April)
   http://chinadoll.as.arizona.edu/~schmidt/90inch.html
 2.3  Advanced Technology   Siding Spring, Australia
   http://msowww.anu.edu.au/home.html
 2.3  Vainu Bappu           Kavalur, India
 2.2  ESO-MPI               Cerro La Silla, Chile
   http://lw10.ls.eso.org/lasilla/lasilla-homepage.html
 2.2  MPI-CAHA              Calar Alto, Spain
   http://www.mpia-hd.mpg.de/CAHA/
 2.2  UH                    Mauna Kea, Hawaii
   http://www.ifa.hawaii.edu/88inch/88inch.html


The largest radio telescopes are:

Largest single dish: Arecibo Observatory (Nat. Astron. & Ionosphere
  Center, Cornell U.)  305-m, Puerto Rico
  http://www.naic.edu/

Largest fully-steerable single dish: Max Planck Institut fuer
  Radioastronomie, 100 m, Effelsburg, Germany
  http://www.mpifr-bonn.mpg.de/effberg.html

Largest mm wave dish: Nobeyama Radio Observatory, 45m, Japan
  http://radio.utsunomiya-u.ac.jp/NAO/nobeyama.html

Largest sub-mm dish: James Clerk Maxwell Telescope (Joint Astron.
  Center = UK, Canada, Netherlands), Mauna Kea, 15 m
  http://www.jach.hawaii.edu/JCMT/

Largest (connected-element) interferometric arrays: 
  Very Large Array (NRAO, New Mexico), 
  27 dishes, each 26.4 m effective diameter
  The maximum separation between antennas is ~35 km.
  http://info.aoc.nrao.edu/doc/vla/html/VLAhome.shtml (not much
  information there for casual browser, except maybe at 
  http://info.aoc.nrao.edu/doc/vla/html/VLA-images.html)

  MERLIN (NRAL, University of Manchester, UK)
  up to 8 dishes, various specifications. 
  The maximum separation between antennae is 217 km (between the
  Cambridge and Knockin dishes). 
  http://www.jb.man.ac.uk/merlin/MERLIN.html
  [MERLIN actually uses radio links between the antenna elements, so
  maybe it should go into a separate category.]


Longest-baseline (dedicated) interferometric array: Very Long Baseline Array
  (NRAO), 10 dishes, each 26.4 m effective diameter, United States
  The maximum separation between antennas is ~8600 km, between the
  islands of St. Croix and Hawaii.
  http://info.aoc.nrao.edu/doc/vlba/html/VLBA.html (again, not much
  for the casual browser, except possibly 
  http://info.aoc.nrao.edu/doc/vlba/html/VLBA-news.html)


Other telescopes of note:

Infrared:
Infrared Space Observatory (ISO) (ESA, launched 1995)
  http://isowww.estec.esa.nl/

Ultraviolet:

Extreme Ultraviolet Explorer (EUVE) (NASA)
   http://www.cea.berkeley.edu/

International Ultraviolet Explorer (IUE) (NASA, PPARC and ESA)
   http://www.vilspa.esa.es/iue/iue.html

X-ray:

X-Ray Astronomy Satellite (SAX) (ESA)
   http://astro.estec.esa.nl/SA-general/Research/Sax/Saxint/saxmain.html

X-Ray Timing Explorer (XTE) (NASA), 2 instruments: PCA & HEXTE
   http://heasarc.gsfc.nasa.gov/docs/xte/XTE.html

ASCA/ASTRO-D (ISAS)
   http://www.astro.isas.ac.jp/xray/mission/asca/ascaE.html

Roentgen Satellite (ROSAT) (MPE)
   http://www.rosat.mpe-garching.mpg.de/

European Space Agency's X-ray Observatory, EXOSAT [defunct] (ESA), 
   3 instruments
   http://heasarc.gsfc.nasa.gov/docs/exosat.html

Einstein, the second High Energy Astronomy Observatory (HEAO-B) [defunct]
   (NASA), 5 instruments: IPC, HRI, SSS, FPCS, & OGS
   http://heasarc.gsfc.nasa.gov/docs/einstein.html

Gamma-ray:

Fred Lawrence Whipple Gamma-Ray Observatory (SAO), a 10 m and 11 m
   instrument
   http://oir-www.harvard.edu/FLWO/FLWO/whipple.html
   http://egret.sao.arizona.edu/

CANGAROO (U. Adelaide & Nippon), 4 4-m cameras
   http://www.physics.adelaide.edu.au/astrophysics/cangaroo.html

Compton Gamma-Ray Observatory (NASA) [space-based], 
   4 instruments: OSSE, EGRET, COMPTEL, & BATSE
   http://cossc.gsfc.nasa.gov/cossc/cgro.html

Cosmic ray:

The High Resolution Fly's Eye Cosmic Ray Detector HiRes 
   http://www.physics.adelaide.edu.au/astrophysics/FlysEye.html

------------------------------

Subject: B.02 What new telescopes/instruments are being built?
Author: Bill Arnett <billa@znet.com>,
 	William Keel <keel@bildad.astr.ua.edu>,
	Steve Willner <swillner@cfa.harvard.edu>,
        Joseph Lazio <lazio@spacenet.tn.cornell.edu>,
	with corrections and additions by many others

(These lists are undoubtedly incomplete.  Additions and corrections
welcome!)

Optical Telescopes (nighttime):

Now actually under construction:
16.4  Very Large Telescope    Cerro Paranal, Chile
      (quartet of 8.2-m telescopes)
      <URL:http://http.hq.eso.org/vlt.html>
11.0  Hobby-Eberly Telescope, Mt. Fowlkes, Texas
      (spectroscopy only)
      <URL:http://www.as.utexas.edu/het/het.html>
      <URL:http://www.astro.psu.edu/het/>
10.0  Keck II                 Mauna Kea, Hawaii
      <URL:http://www2.keck.hawaii.edu:3636/>
      <URL:http://astro.caltech.edu/observatories/keck/>
 8.0  Gemini North            Mauna Kea, Hawaii
 8.0  Gemini South            Cerro Pachon, Chile
      <URL:http://www.gemini.edu/>
 8.2  Subaru (JNLT)           Mauna Kea, Hawaii
      <URL:http://www.clarkson.edu/clarkson/corning/corning.html>
 6.5  MMT		      Mt. Hopkins, Arizona
      (replace current six mirrors with single one; see B.01)
      <URL:http://sculptor.as.arizona.edu/foltz/www/mmt.html>
 5.1  Liquid Mirror         Malcolm Knapp Research Forest, British Columbia
      (mercury mirror)
      <URL:http://www.geop.ubc.ca/~cabanac/limits.html>
 3.7  Advanced Electro-Optical System     Mt Haleakala, Hawaii
      <URL:http://www.plk.af.mil/PLhome/PA/FACTSHEETS/eleoptcl.html>
 3.5  Telescopio Nazionale Galileo        La Palma, Canary Islands, Spain
      <URL:http://www.pd.astro.it/TNG/TNG.html>


Others likely to start soon:
Large Binocular Telescope, (Italy; U. Arizona), pair of 8-m
  telescopes, Mt. Graham, Arizona 
  http://lbtwww.arcetri.astro.it/

Canary Islands Large Telescope Canary Islands, Spain, 10 m segmented mirror
  http://www.iac.es/10m/uk10m.html

Magellan (Carnegie Institution Observatories), 6.5 m, Las Campanas
  http://medusa.as.arizona.edu/mlab/mag.html


Solar Telescope:

Global Oscillation Network Group (GONG), six sites around the world
  for velocity imaging
  http://helios.tuc.noao.edu/gonghome.html 

Radio telescopes:

Submillimeter Array, (Smithsonian Astrophysical Observatory), six 6-m
  dishes at Mauna Kea
   http://sma2.harvard.edu/index.html

Millimeter Array (MMA) (NRAO)
   http://info.cv.nrao.edu/mma.html

Green Bank Telescope (NRAO)
   http://info.gb.nrao.edu/GBT/GBT.html

X-ray:

Astro-E (ISAS)
   http://www.astro.isas.ac.jp/xray/mission/astroe/astroeE.html

Advanced X-ray Astrophysics Facility (NASA)
   http://hea-www.harvard.edu/asc/axaf-welcome.html

High-Throughput X-Ray Spectroscopy Mission (ESA)
   http://astro.estec.esa.nl/XMM/xmm.html

Neutrino:

Antarctic Muon and Neutrino Detector Array (AMANDA)
   http://spice2.physics.wisc.edu/amanda.html

Deep Undersea Muon and Neutrino Detection (DUMAND)
   http://web.phys.washington.edu/local_web/dumand/aaa_dumand_home.html

Gravitational Waves:

LIGO, (US), 4 km path
  http://www.ligo.caltech.edu/

Virgo, (Italy), 3 km path
  http://www.pi.infn.it/virgo/virgoHome.html

------------------------------

Subject: B.03 What is the resolution of a telescope?
Author: Steve Willner <swillner@cfa.harvard.edu>

The _limiting_ resolution of a telescope can be no better than a size
set by its aperture, but there are many things that can degrade the
resolution below the theoretical limit.  Obvious examples are
manufacturing defects and the Earth's atmosphere.  Another interesting
one is the addition of a central obstruction (e.g., secondary mirror)
which degrades the resolution for most practical purposes even though
it _shrinks_ the size of the central diffraction disk.  The problem is
that even though the disk diameter decreases, the central disk
contains a smaller fraction of the incident light (and the rings
contain more).  This is why modest sized refractors often outperform
reflectors of the same size.

Giving a precise value for the resolution of an optical system depends
on having a precise definition for the term "resolution."  That isn't
so easily done; the most general definition must be based on something
called "modulation transfer function."  If you don't want to be
bothered with that, it's enough to note that in all but pathological
cases, the diameter (full width at half maximum in radians) of the
central diffraction disk will be very close to the wavelength in use
divided by the diameter of the entrance pupil.  (The often seen factor
of 1.22 refers to the radius to the first null for an _unobstructed_
aperture, but a different factor will be needed if there is a central
obstruction.)  In practical units, if the wavelength (w) is given in
microns and the aperture diameter (D) in meters, the resolution in
arcseconds will be:
  R = 0.21 w/D .

------------------------------

Subject: B.04 What's the difference between astronomy and astrology?
Author: Phillippe Brieu <phillipe@umich.edu>

Although astronomy and astrology are historically related and many
individuals were interested in both, there is today no connection
between the two.  Hence two different USENET newsgroups exist:
sci.astro (for the former) and alt.astrology (for the latter).  DO NOT
CONFUSE THEM.

Astronomy is based on the laws of physics (and therefore mathematics)
and aims at describing what is happening to the universe based on what
we observe today.  Because the laws of physics are constant (as far as
we can tell), astronomy can also explain how the universe behaved in
the past and can propose a limited number of possible scenarios for
its future (see FAQ entry about Big Bang).  Everyday life applications
of astronomy include calculations/predictions of sunrise/sunset times,
moon phases, tides, eclipse locations, comet visibility, encounters
between various celestial bodies (e.g., SL9 comet crash onto Jupiter
in 1994), spacecraft trajectories, etc.

Astrology on the other hand claims it can predict what will happen to
individuals (or guess what is happening to them), or to mankind, based
on such things as solar system configurations and birth dates.  Common
applications include horoscopes and such.  Regardless of whether there
is scientific support for astrology, its goal and methods are clearly
distinct from those of astronomy.

------------------------------

Subject: B.05 Is there scientific evidence for/against astrology?

This question should be discussed in alt.astrology and/or sci.skeptic,
not in sci.astro.

------------------------------

Subject: B.06 What about God and the creation?
Author: Joseph Lazio <lazio@spacenet.tn.cornell.edu>

Astronomy is silent on the matter of God and the creation.

Astronomy is based on applying the laws of physics to the Universe.
These laws of physics attempt to describe the natural world and are
based on experiments here on Earth and our observations of the rest of
the Universe.  The key words are "natural world."  It is obvious that
the existence of a supernatural being(s) is outside the realm of the
natural laws.

It should be noted that people do use the results of astronomy to
attempt to deduce the existence of God (or gods).  Unfortunately, one
can reach two, equally valid conclusions:

  * Many atheists (including some astronomers) argue that the
    regularity of the natural world, combined with our apparent lack
    of distinction in it (the Earth is just one planet, around one
    star, in one galaxy, etc.), are compelling reasons not to believe
    in any god.  

  * Many theists (including ordained ministers and priests who are
    also astronomers) find the study of the natural world another
    means of understanding God.  The beauty, order, and sheer scope of
    the natural world are profound clues to the power and intelligence
    which created it all. 

Since sci.astro is devoted to science of astronomy (i.e., the natural
world), sci.astro is not the appropriate forum for such a religious
debate.  If you would like to discuss such things, you should go to
talk.origins, talk.religion.*, or maybe soc.religion.*

------------------------------

Subject: B.07 What kind of telescope should I buy?

 See the Purchasing Amateur Telescopes FAQ, posted regularly to
sci.astro.amateur or <URL:http://www.scs.uiuc.edu/~nash/saafaq.html>.

------------------------------

Subject: B.08 What are the possessive adjectives for the planets?
Author: Steve Willner <swillner@cfa.harvard.edu>,
	Andrew Christy <christy@rschp2.anu.edu.au>

Mercury  Mercurian    mercurial
Venus	 Venerian     venereal
	 Venusian
         Cytherean
Earth	 Terrestrial
	 Telluric
Mars	 Martian      martial
         Arean
Jupiter  Jovian	      jovial
Saturn	 Saturnian    saturnine
Uranus	 Uranian
Neptune	 Neptunian
Pluto	 Plutonian

The first form(s) refers to the planet as an object (e.g., "Saturnian
rings").  The second form refers to human characteristics historically
associated with the planet's astrological influence or with the god or
goddess represented by the planet (e.g., "a jovial individual").

------------------------------

Subject: B.09 Are the planets associated with days of the week?
Author:	Steve Willner <swillner@cfa.harvard.edu>,
	Andrew Christy <christy@rschp2.anu.edu.au>,
	Ken Arromdee <arromdee@blaze.cs.jhu.edu>,
	Giuseppe De Marco <gdemarco@freenet.hut.fi>

Surprisingly, yes.  This comes from the historical association of the
"planets" with gods and goddesses.  In ancient times, the word
"planets" was from the Greek for "wanderers" and referred to objects
in the sky that were not fixed like the stars.  Some of these
associations are clearer in English, especially if we compare with
names of Norse or Old English gods/goddesses, while others are clearer
from comparing French/Spanish with the Roman gods and goddesses.  We
have:

         Sun      Moon    Mars     Mercury    Jupiter   Venus    Saturn

Roman             Luna    Mars     Mercury    Jupiter   Venus    Saturn
Norse                     Tiw      Woden      Thor      Freya

French   dimanche lundi   mardi    mercredi   jeudi     vendredi samedi
Spanish  domingo  lunes   martes   miercoles  jueves    viernes  sabado
Italian  Domenica Lunedi  Martedi  Mercoledi  Giovedi   Venerdi  Sabato
English  Sunday   Monday  Tuesday  Wednesday  Thursday  Friday   Saturday
German   Sonntag  Montag  Dienstag Mittwoch   Donnerstag Freitag Samstag


 Notes:
1. Sun:  Dimanche and domingo are from the Latin for "Day of the Lord."
2. Saturn:  Sabado is from "Sabbath."
3. German and English use Teutonic, not Scandinavian forms of the God
   names, e.g., "Woden" in "Wednesday," not "Odin," which is the Norse
   equivalent. The God of Tuesday was Tiw.
4. Russian numbers three days (Tuesday = 2nd, Thursday = 4th, and
   Friday= 5th) and does not use God/Planet names for the rest.


This association between planets and days of the week holds in at
least some non-European languages as well.  (How many?)

In Japanese the days Tuesday through Saturday (and the associated
planets) are named after the five Asian elements, rather than gods.

                Japanese
          days           planets

Sun       nichiyoubi     hi    (same kanji as nichi)
Moon      getsuyoubi     tsuki (same kanji as getsu)
Mars      kayoubi        kasei
Mercury   suiyoubi       suisei
Jupiter   mokuyoubi      mokusei
Venus     kinyoubi       kinsei
Saturn    doyoubi        dosei

------------------------------

Subject: B.10  Why does the Moon look so big when it's near the horizion?
Author: Steve Willner <swillner@cfa.harvard.edu>

The effect is an optical illusion.  You can verify this for yourself
by comparing the size of the Moon when it's on the horizon to that of
a coin held at arm's length.  Repeat the measurement when the Moon is
overhead.  You will find the angular size unchanged within the
accuracy of the measurement.

In fact the apparent vertical diameter of the Moon is a bit smaller on
the horizon than overhead because of atmospheric refraction.  A really
precise measurement will reveal that the horizontal diameter is (on
average) about 1.7% smaller when the Moon is horizontal because you
are farther from it by approximately one Earth radius.

The Sun, incidentally, shows the much same effects as the Moon, though
it's a really bad idea to look directly at the Sun without proper eye
protection (NOT ordinary sunglasses).  The change in apparent angular
diameter is, of course, less than 0.01% instead of 1.7% because the
Sun is farther away.

I'm not aware of any definitive explanation of the cause of the
optical illusion.  One possibility is that objects on the horizon look
bigger simply because there is something nearby with which to compare.
Another is that our brains interpret things seen in a horizontal
direction as larger.  The little reading I've done suggests that the
latter is a better explanation, but anybody having a definitive answer
is invited to write a better answer to this question!

------------------------------

Subject: B.11  Is it O.K. to look at the Sun or solar eclipses using
	exposed film? CDs?
Author: Joseph Lazio <lazio@spacenet.tn.cornell.edu>,
	Steve Willner <swillner@cfa.harvard.edu>

This question appears most frequently near the time of solar eclipses.

The short answer is no!  The unobscured surface of the sun is as
bright as ever during a partial eclipse and just as capable of causing
injury.  The injured area on the retina may be a bit smaller, of
course, but that's no reason to risk damage.  Moreover, there are no
nerve endings in the retina, so one can do permanent damage without
being aware of it.

People have proposed a host of methods for viewing the Sun, including
exposed film and CDs.  These home-grown methods typically suffer from
two flaws.  First, they do not cut out enough visible light.  Second,
they provide little protection against ultraviolet or infrared light.

The only safe method for viewing the Sun directly is using No. 14
arc-welder filter or a metallicized glass or Mylar filter.  A local
hardware store or construction supply store should carry or know where
to obtain arc-welder filters.  Many astronomy magazines carry ads for
solar filters.

Whatever filter you use, inspect it to make sure it has not been
damaged.  Even a pinhole can let through enough light to cause injury.
If you use a filter over a telescope or binocular, make sure the
filter is firmly attached and cannot come off accidentally!  Never use
an eyepiece filter, which can overheat and crack.  Any filter should
cover the entire entrance aperture (or more precisely, any part of the
entrance aperture that isn't covered by something completely opaque).
If using only one side of a binocular, cover the other side.

An alternative way to view the sun is in projection.  You can use a
pinhole camera or a telescope, eyepiece, and screen.  Many observing
handbooks illustrate suitable arrangements.  This method is not only
safe, it can give a magnified image and make it easier to see details.

If you are lucky enough (or put in the advance planning) to see a
total solar eclipse, the total phase can be enjoyed with no eye
protection whatsoever.  In fact, experienced eclipse-goers often cover
one eye with a patch for several minutes before totality so the eye
will be dark-adapted during totality.  Just be sure to look away (or
through your filter again) the instant totality is over.

------------------------------

Subject: B.12 Can stars be seen in the daytime from the bottom of a
	tall chimney, a deep well, or deep mine shaft?
Author: Michael Dworetsky <mmd@star.ucl.ac.uk>
 
The short answer is no (well, almost no).  The long answer is given by
David Hughes in the Quarterly Journal of the Royal Astron. Soc., 1983,
vol. 24, pp 246-257.

This mistaken notion was first mentioned by Aristotle and other
ancient sources, and was widely assumed to be correct by many literary
sources of the 19th century, and even believed by some astronomers.
But every astronomer who has ever tested this by experiment came away
convinced it was impossible.

If you want to try an interesting experiment to see why it is believed
that whatever people see up chimneys cannot be stars, try the
experiment at night, as I have done, using a cardboard tube centre
from a paper towel roll (mine had an opening of 25 square degrees).
You will see that, at random, you will seldom include one visible
star, rarely two, and virtually never more than two, in the field.

Separate experiments to attempt to see Vega and Pollux through tall
chimneys were performed by J. A. Hynek and A. N.  Winsor.  They were
unable to detect the stars under near perfect conditions, even with
binoculars.

The daytime sky is simply too bright to allow us to see even the
brightest stars (although Sirius can sometimes be glimpsed just after
the Sun rises if you know exactly where to look.)  Venus can be seen
as a tiny white speck but again, you have to be looking exactly at the
right spot.

The most likely explanation for the old legend is that stray bits of
rubbish get caught in the updraft and catch the sunlight as they
emerge from the chimney.  It is possible to see stars in the daytime
with a good telescope, as long as it has been prefocused and can be
accurately pointed at a target.
 
------------------------------

Subject: B.13 Why do eggs balance on the equinox?
Author: Bob Riddle <briddlkc@cyclops.pei.edu>

Luck.  In short, there's no validity to the idea that eggs can only be
balanced on the equinox.

This question often arises during March and September, when it is not
unusual to hear, see, or read news reports about the equinox occurring
during that month.  It is also not unusual to hear news reports being
able to balance an egg on the equinox day.  In fact many times these
reports will highlight a classroom wherein the students are shown
trying to balance eggs.  Naturally some eggs will balance and others
will not---one time, then perhaps do differently the next time.

The focus in these reports, however, seems to be on the eggs that do
balance rather than the observations from the experiment that not all
eggs balanced the first time tried, nor did all eggs always balance,
or perform the same way every time.

There are a number of problems with the idea of balancing an egg:

1. Typically, explanations about the balancing act involve gravity.
One explanation that I've heard suggested that gravity is "balanced"
when the sun is over the earth's equator.  Another gravity-based
explanation is that the sun exerts a greater gravitational attraction
on the earth on these two days.  If gravity is involved in balancing
the egg shouldn't other objects balance as well? Or is gravity
selective such that only an egg is affected on this particular day?

2. The equinox is a certain day, while the sun is actually at the
equinox point for an instant (0 degrees on the celestial equator and
12 hours within the constellation Virgo). Therefore, shouldn't the egg
only be balanced at the specific time that the sun reaches that
position?

3. If the Sun's gravity is involved, shouldn't latitude have an
effect?  For example I live at 40 degrees north.  Shouldn't the egg
lean at an angle pointing towards the sun where I live---and if so,
then it should only be standing straight up at the equator?

You can of course conduct your own experiment.  Issues to consider
when designing your experiment include, Would the same egg balance on
any other day(s) during the year?  What would be the results of
standing the same egg under the same physical conditions and at the
same time each day throughout the year?

------------------------------

Subject: How do I become an astronomer?  What school should I attend?
Author: Suzanne H. Jacoby <sjacoby@noao.edu>

This material is extracted from the National Optical Astronomy
Observatories' Being an Astronomer FAQ,
<URL:http://www.noao.edu/education/astfaq.html>.

Astronomers are typically good at math, very analytical, logical, and
capable of sound reasoning (about science, anyway).  Computer literacy
is a necessity.  While not all astronomers are skilled computer
programmers, all should be comfortable using a computer for editing
files, transferring data across networks, and analyzing their
astronomical data and images.  Other valuable traits are patience and
determination for sticking to a difficult problem or theory until
you've seen it through---which can take years.  The final product of
scientific research is the dissemination of the knowledge gained, so
don't overlook the importance of communication skills like effective
public speaking at professional meetings and the ability to publish
well written articles in scientific journals.

Many of these skills are developed during one's education and
training.  In the U.S., a typical astronomer will obtain a Bachelor of
Science (B.S.) degree in a physical science or mathematics, then
attend graduate school for 5--7 years to obtain a Ph.D.  After earning
a Ph.D., it is common to take a postdoctoral position, a temporary
appointment which allows an astronomer to concentrate on his or her
own research for about two to three years.  These days, most people
take a second postdoc or even a third before they are able to land a
faculty or scientific staff position.

If you want to become an astronomer, a general principle is to obtain
as broad and versatile an education as possible while concentrating in
mathematics, physics, and computing.  It is not critical that your
Bachelor's degree be in astronomy.  Students with a strong core of
physics classes in addition to some astronomy research experience are
most likely to be accepted to graduate programs in astronomy.

Additional information on astronomy as a career can be obtained from
the American Astronomical Society,
<URL:http://www.aas.org/education/career.html>, and the
Harvard-Smithsonian Center for Astrophysics (contact their
Publications Department, MS-28, 60 Garden Street, Cambridge, MA 01238,
USA, or call 617-495-7461, ask for the brochure "Space for Women").

