not in the near future
the last is only reserved for the super rich 
Astrometry
Astrometry is a part of astronomy and deals with
the positions of stars and other celestial bodies, their distances
and movements. Part of astrometry involves creating the cosmic
distance ladder.
It is one of the oldest subfields of the science, the successor to
the more qualitative study of positional astronomy. Astrometry
dates back at least to Hipparchus, who compiled the first catalogue
of stars visible to him and in doing so invented the brightness
scale basically still in use today. Modern astrometry was founded
by Friedrich Bessel with his Fundamenta astronomiae, which gave the
mean position of 3222 stars observed between 1750 and 1762 by James
Bradley.
Apart from the fundamental function of providing astronomers with a
reference frame to report their observations in, astrometry is also
fundamental for fields like celestial mechanics, stellar dynamics
and galactic astronomy. In observational astronomy, astrometric
techniques help identify stellar objects by their unique motions.
It is also instrumental for keeping time, in that UTC is basically
the atomic time synchronized to Earth's rotation by means of exact
observations.
There have been several important advances in astrometry.
- Sundials were effective at measuring time.
- Astrolabes were invented for measuring celestial
angles.
- Astrometric applications led to the development of
spherical geometry.
- Careful measurement of planetary motions by Tycho Brahe proved
the Copernican principle, that Earth revolves
about the Sun.
- The sextant dramatically improved measurement of
celestial angles.
- The development of cheap charge coupled devices, software, and
telescopes allowed for large-scale amateur astrometric observation
of minor planets.
Another was the use of Cepheid variable stars to measure the
distance to nebulae, which led to the discovery of other galaxies
by Edwin Hubble. Hubble used triangulation on nearby Cepheids, and
correlated the Cepheid's period to their absolute brightness. Then
by measuring the period and brightness of Cepheids in nebulae, he
established their distance by their brightness.
Hubble used Cepheids to discover and calibrate distance with the
red shift shown by distant galaxies.
From 1989 to 1993, the European Space Agency's Hipparcos satellite
performed astrometric measurements resulting in a catalogue of
positions accurate to 20-30 milliarcsec for over a million
stars.
Astronomers use astrometric techniques for the tracking of
near-Earth objects. It has been also been used to detect extrasolar
planets by measuring the doppler shift they cause in their parent
star's spectrum. NASA's planned Space Interferometry Mission will
utilize astrometric techniques to detect gas giants around other
stars, and perhaps even terrestrial planets nearby.
Astrometric measurements are used by astrophysicists to constrain
certain models in celestial mechanics. By measuring the velocities
of pulsars, it is possible to put a limit on the asymmetry of
supernova explosions. Also, astrometric results are used to
determin the distribution of dark matter in the galaxy.
Astrometrics is the science of stellar
measurements and motion. Astrometrics was used, during the 1990s,
to detect extrasolar gas giants orbiting various solar systems.
This was done by observing the "stellar wobble" of a star and
calculating what kinds of gravitational forces would cause such
motion; it was then determined that planetary forces must be
affecting the stars in question.
Issue #6
Astronomy Picture of the Day
2005 February 27
The Solar Spectrum
Explanation: It is
still not known why the Sun's light is missing some colors. Shown
above are all the visible colors of the Sun, produced by passing
the Sun's light through a prism-like device. The above spectrum was
created at the McMath-Pierce Solar Observatory and shows, first
off, that although our yellow-appearing Sun emits light of nearly
every color, it does indeed appear brightest in yellow-green light.
The dark patches in the above spectrum arise from gas at or above
the Sun's surface absorbing sunlight emitted below. Since different
types of gas absorb different colors of light, it is possible to
determine what gasses compose the Sun. Helium, for example, was
first discovered in 1870 on a solar spectrum and only later found
here on Earth. Today, the majority of spectral absorption lines
have been identified - but not all.
Credit &
Copyright: Nigel Sharp (NSF), FTS, NSO, KPNO, AURA, NSF
Astrophysics
Astrophysics is the branch of astronomy that deals
with the physics of the universe, including the physical properties
(luminosity, density, temperature and chemical composition) of
astronomical objects such as stars, galaxies, and the interstellar
medium, as well as their interactions. The study of cosmology is
theoretical astrophysics at its largest scale; conversely, since
the energies involved in cosmology, especially the Big Bang, are
the largest known, the observations of the cosmos also serve as the
laboratory for physics at its smallest scales as well.
Spiral Galaxy ESO
269-57
In practice, virtually all modern astronomical research involves a
substantial amount of physics. The name of a school's doctoral
program ("Astrophysics" or "Astronomy") in many places like the
United States often has to do more with the department's history
than with the contents of the programs.
History
Although astronomy is as old as recorded history, it was long
separated from the study of physics. In the Aristotelian worldview,
the celestial pertained to perfectionbodies in the sky being
perfect spheres moving in perfectly circular orbitswhile the
earthly pertained to imperfection; these two realms were seen as
unrelated.
For centuries, the apparently common-sense view that the Sun and
other planets went round the Earth went unquestioned, until
Nicolaus Copernicus suggested in the 16th century that the Earth
and all the other planets in the Solar System orbited the Sun.
Galileo Galilei made quantitative measurements central to physics,
but in astronomy his observation didn't have astrophysical
significance.
The availability of accurate observational data led to research
into theoretical explanations for the observed behavior. At first,
only ad-hoc rules were discovered, such as Kepler's laws of
planetary motion, discovered at the start of the 17th century.
Later that century, Isaac Newton, bridged the gap between Kepler's
laws and Galileo's dynamics, discovering that the same laws that
rule the dynamics of objects on earth rules the motion of planets
and the moon. Celestial mechanics, the application of Newtonian
gravity and Newton's laws to explain Kepler's laws of planetary
motion, was the first unification of astronomy and physics.
After Isaac Newton published his Principia, maritime navigation was
transformed. Starting around 1670, the entire world was measured
using essentially modern latitude instruments and the best
available clocks. The needs of navigation provided a drive for
progressively more accurate astronomical observations and
instruments, providing a background for ever more available data
for scientists.
At the end of the 19th century it was discovered that, when
decomposing the light from the Sun, a multitude of spectral lines
were observed (regions where there was less or no light).
Experiments with hot gases showed that the same lines could be
observed in the spectra of gases, specific lines corresponding to
unique chemical elements. In this way it was proved that the
chemical elements found in the Sun (chiefly hydrogen) were also
found on Earth. Indeed, the element helium was first discovered in
the spectrum of the sun and only later on earth, hence its name.
During the 20th century, spectrometry (the study of these spectral
lines) advanced, particularly as a result of the advent of quantum
physics that was necessary to understand the astronomical and
experimental observations.
Observational astrophysics
Most astrophysical processes cannot be reproduced in laboratories
on Earth. However, there is a huge variety of astronomical objects
visible all over the electromagnetic spectrum. The study of these
objects through passive collection of data is the goal of
observational astrophysics.
The equipment and techniques required to study an astrophysical
phenomenon can vary widely. Many astrophysical phenomena that are
of current interest can only be studied by using very advanced
technology and were simply not known until very recently.
The majority of astrophysical observations are made using the
electromagnetic spectrum.
- Radio astronomy
studies radiation with a wavelength greater than a few millimeters.
Radio waves are usually emitted by cold objects, including
interstellar gas and dust clouds. The cosmic microwave background
radiation is the redshifted light from the Big Bang. Pulsars were
first detected at microwave frequencies. The study of these waves
requires very large radio telescopes.
- Infrared
astronomy studies radiation with a wavelength that is too
long to be visible but shorter than radio waves. Infrared
observations are usually made with telescopes similar to the usual
optical telescopes. Objects colder than stars (such as planets) are
normally studied at infrared frequencies.
- Optical
astronomy is the oldest kind of astronomy. Telescopes and
spectroscopes are the most common instruments used. The Earth's
atmosphere interferes somewhat with optical observations, so
adaptive optics and space telescopes are used to obtain the highest
possible image quality. In this range, stars are highly visible,
and many chemical spectra can be observed to study the chemical
composition of stars, galaxies and nebulae.
- Ultraviolet, X-ray and
gamma ray astronomy study very energetic processes such as
binary pulsars, black holes, magnetars, and many others. These
kinds of radiation do not penetrate the Earth's atmosphere well, so
they are studied with space-based telescopes such as RXTE, the
Chandra X-ray Observatory and the Compton Gamma Ray
Observatory.
Other than electromagnetic radiation, few things may be observed
from the Earth that originate from great distances. A few
gravitational wave observatories have been constructed, but
gravitational waves are extremely difficult to detect. Neutrino
observatories have also been built, primarily to study our Sun.
Cosmic rays consisting of very high energy particles can be
observed hitting the Earth's atmosphere.
Observations can also vary in their time scale. Most optical
observations take minutes to hours, so phenomena that change faster
than this cannot readily be observed. However, historical data on
some objects is available spanning centuries or millennia. On the
other hand, radio observations may look at events on a millisecond
timescale (millisecond pulsars) or combine years of data (pulsar
deceleration studies). The information obtained from these
different timescales is very different.
The study of our own Sun has a special place in observational
astrophysics. Due to the tremendous distance of all other stars,
the Sun can be observed in a kind of detail unparalleled by any
other star. Our understanding of our own sun serves as a guide to
our understanding of other stars.
The topic of how stars change, or stellar evolution, is often
modelled by placing the varieties of star types in their respective
positions on the Hertzsprung-Russell diagram, which can be viewed
as representing the state of a stellar object, from birth to
destruction. The material composition of the astronomical objects
can often be examined using:
- spectroscopy
- radio astronomy
- astronomical observatories
Theoretical astrophysics
Theoretical astrophysicists create and evaluate models to reproduce
and predict observations. They use a wide variety of tools which
include analytical models (for example, polytropes to approximate
the behaviors of a star) and computational numerical
simulations.
Dark matter and dark energy are currently topics in astrophysics,
as their discovery and controversy originated during the study of
the galaxies.
Issue #7
Astronomy Picture of the Day
2005 February 28
Unusual Plates on Mars
Explanation: What
are those unusual plates on Mars? A leading current interpretation
holds that they are blocks of ice floating on a recently frozen sea
covered by dust. The unusual plates were photographed recently by
the European Space Agency's Mars Express spacecraft currently
orbiting Mars. Oddly, the region lies near the Martian equator and
not near either of Mars' frozen polar caps. Without being covered
by dust, any water or ice near away from the poles would quickly
evaporate right into the atmosphere. Evidence that the above-imaged
plates really are dust-covered water-ice includes a similarity in
appearance to ice blocks off Earth's Antarctica, nearby surface
fractures from which underground water could have flowed, and the
shallow depth of the craters indicating that something is filling
them in. If correct, the low abundance of craters indicates that
water may have flowed on Mars as recently as five million years
ago.
Credit: G. Neukum
(FU Berlin) et al., Mars Express, DLR, ESA
Cosmology
Cosmology is the study of the large-scale
structure and history of the universe. In particular, it deals with
subjects regarding its origin and evolution. It is studied by
astronomy, philosophy, and religion.
Physical cosmology
- The Big Bang
-- The Friedmann-Lemaître-Robertson-Walker metric
-- The shape of the universe in big bang theory
- Cosmological principle
- Hubble Law
-- Comoving distance
- Cosmic microwave background (CMB)
-- Cosmic variance
- Big bang nucleosynthesis
- Galaxy Formation and Evolution
- Large Scale Structure of the Cosmos - few 100 Mpc - a few percent
of the horizon
- Dark matter
- Dark energy
- Cosmic inflation
- Topological defects
- The Ultimate fate of the Universe
Due to the extreme conditions believed to be present during the
first minutes of the universe's history, cosmologists often
co-operate with scientists from areas such as particle
physics.
Other cosmologies
Other cosmologies include:
- Philosophical cosmology
-- Presocratic philosophers
-- Anthropic principle
- Religious cosmology
Issue #8
Astronomy Picture of the Day
2005 March 1
NGC 1531/2: Interacting Galaxies
Explanation: This
dramatic image of an interacting pair of galaxies was made using
8-meter Gemini South telescope at Cerro Pachon, Chile. NGC 1531 is
the background galaxy with a bright core just above center and NGC
1532 is the foreground spiral galaxy laced with dust lanes. The
pair is about 55 million light-years away in the southern
constellation Eridanus. These galaxies lie close enough together so
that each feels the influence of the other's gravity. The
gravitational tug-of-war was triggered star formation in the
foreground spiral as evidenced by the young, bright blue star
clusters along the upper edge of the front spiral arm. Though the
spiral galaxy in this pair is viewed nearly edge-on, astronomers
believe the system is similar to the face-on spiral and companion
known as M51, the Whirlpool Galaxy.
Credit &
Copyright: T. Rector (U. Alaska Anchorage), Gemini Obs.,
AURA, NSF
Galaxy formation and
evolution
In astrophysics, the questions of galaxy formation and evolution
are:
- How, from a homogeneous universe, did we obtain the very
inhomogeneous one we live in?
- How did galaxies form?
- How do galaxies change over time?
The formation of galaxies is still one of the most active research
areas in astrophysics; and, to some extent, this is also true for
galaxy evolution. Some ideas, however, are now widely
accepted.
A spectacular head-on collision
between two galaxies is seen in this NASA Hubble Space Telescope
true-color image of the Cartwheel Galaxy.
After the Big Bang, the universe had a period when it was
remarkably homogeneous, as can be observed in the Cosmic Microwave
Background, the fluctuations of which are less than one part in one
hundred thousand.
The most accepted view is that all the structure we observe today
was formed as a consequence of the growing of primordial
fluctuations by gravitational instability. Recent data strongly
suggests that the first galaxies formed as early as 600 million
years after the Big Bang, much earlier than astronomers had
previously believed. That leaves hardly enough time for the tiny
primordial instabilities to grow sufficiently forming protogalaxies
into galaxies.
A great deal of the research in this area is focused on components
of our own Milky Way, since it is the easiest galaxy to observe.
The observations which must be explained in, or at least not at
odds with, a theory of galactic evolution, include:
- The stellar disk is quite thin, dense, and rotates.
- The stellar halo is very large, sparse, and does not rotate (or
has perhaps even a slight retrograde rotation), with no apparent
substructure.
- Halo stars are typically much older and have much lower
metallicities than disk stars (there is a correlation, but there is
no absolute connection between these data).
- Some astronomers have identified an intermediate population of
stars, variously called the "metal weak thick disk", the
"intermediate population II", et al. If these are indeed a distinct
population, they would be described as metal-poor (but not as poor
as the halo stars), old (but not as old as the halo stars), and
orbiting very near the disk, in a sort of "puffed-up", thicker disk
shape.
- Globular clusters are typically old and metal-poor as well, but
there are a few which are not nearly as metal-poor as most, and/or
have some younger stars. Some stars in globular clusters appear to
be as old as the universe itself (by entirely different measurement
and analysis methods)!
- In each globular cluster, all the stars were born at virtually
the same time (except for a few globulars that show multiple epochs
of star formation).
- Globular clusters with smaller orbits (closer to the galactic
center) have orbits which are somewhat flatter (less inclined to
the disk), and less eccentric (more circular), while those further
out have orbits in all inclinations, and tend to be more
eccentric.
- High Velocity Clouds, clouds of neutral hydrogen are "raining"
down on the galaxy, and presumably have been from the beginning
(these would be the necessary source of a gas disk from which the
disk stars formed).
- and many more interesting data.
Issue #9
Astronomy Picture of the Day
2005 March 2
The Powerful Sumatra-Andaman Islands
Earthquake
Explanation:
December's 9.0 earthquake has likely shortened Earth's day by about
three microseconds and may also have tweaked Earth's rotational
wobble. The megathrust earthquake occurred as the Indian tectonic
plate slid further beneath the Burma tectonic plate. The earthquake
was the fourth most powerful since the year 1900 and triggered
tsunamis that tragically killed over 250,000 people in nearby
coastal regions. In the above map, the yellow star indicates the
location of the main earthquake, while circles show the locations
of large aftershocks. The Sumatra-Andaman Islands earthquake's
effect on the Earth's rotation was sudden but much smaller than the
accumulated effects of other surface events such as an El
Nino.
Credit: USGS
