Astronomy 1100 Introduction to Astrophysics

1
Astronomy 1100Introduction to Astrophysics

• Goals to develop a knowledge of some of the
  basic tools used in the study of astronomy and
  astrophysics, and to gain practical experience
  with them. The field depends highly on accurate
  observations to make deductions about the
  universe around us, and it is important to
  understand which observations are fundamental and
  which are subject to large observational
  uncertainties.
• Emphasis is placed on the development of critical
  judgment to separate observational information
  from proposed physical models.

2
Astronomical Factoids Ancient Numerology 20 1
20 2 10 4 5 Numbers 1, 2, 4, 5, 10 are
factors of 20. But 1 2 4 5 10 22 gt
20 So 20 is an abundant number. 22 1 22 2
11 Numbers 1, 2, 11 are factors of 22. But 1 2
11 14 lt 22 So 22 is a deficient number.
3
6 1 6 2 3 Numbers 1, 2, 3 are factors of
6. But 1 2 3 6 6 ! So 6 is a perfect
number. The first five known perfect numbers
are 6, 28, 496, 8128, and 33,550,336. They form
a rather select group.
4
A perfect number is the sum of its proper
positive divisors, e.g.6 1 2 3 1 ? 2 ?
328 1 2 4 7 14 1 ? 2 ? 14 1 ? 4 ?
7Very few perfect numbers exist.6, 28, 496,
8128, 33,550,336, 8,589,869,056?
5
The astronomical connection 6 the number of
nights it takes the Moon to go from a thin
crescent after New Moon to First Quarter
phase. 28 the number of nights it takes for the
Moon to go from a thin crescent after New Moon
until it disappears from view at the next New
Moon (moonth 29½ days). Coincidence? 6
number of sides on a cube 360 6 6 10
number of degrees in a circle ? 365, the number
of days in a year 24 6 4 number of hours in
a day
6
(No Transcript)
7
The Phases of the Moon
8
The Phases of the Moon
9
Phases of the Moon
10
Pictures in the Full Moon
11
The Man in the Moon
The Lady in the Moon
The Beetle
The Rabbit
12
Development of the 24-hour Day
13
May 3, 1990.
April 19, 1990.
May 26, 1990.
14
Moonrise over Seattle
15
Sunset and Moonset?
16

17
Development of the 24-hour Day The day can be
separated into four (4) distinct
segments Sunrise to Noon (high point) Noon to
Sunset Sunset to Midnight (opposite of
noon) Midnight to Sunrise If each of these
segments is marked by the Suns movement through
6 smaller segments (6 is a perfect number) called
hours, then the day consists of 24 hours.
18
Circular units in Astronomy A complete circle
therefore consists of 360 6 ? 6 ? 10 units
called degrees (), or 24 4 ? 6 units called
hours (h). Subdivisions are 1 60 arcminutes
(') 1' 60 arcseconds (") 1h 60 minutes (m) 1m
60 seconds (s)
19
Plane Trigonometry Recall triangles in plane
trigonometry. A, B, and C denote angles a, b,
and c denote opposite sides Interrelated
through
20
(No Transcript)
21
Scientific Notation in Astronomy As in physics,
mks units are normally used in conjunction with
powers of ten notation and proper round-off
rules. Astronomers can be lazy at times, however,
and often stray from the standard usage. For
example, in the study of stellar atmospheres, cgs
units are used (an older variant of mks units).
In stellar astronomy, the units of length, mass,
and time are also expressed typically as parsecs
(pc), kiloparsecs (kpc), or Megaparsecs (Mpc),
solar masses (M?), and years (yr) or Megayears
(Myr).
22
Some examples. 1. The Suns disk has an average
angular diameter of 1920" while the Moons disk
has an average angular diameter of 1865". The
Suns average distance is 1.496 ? 108 km, while
that of the Moon is 3.844 ? 105 km. What are the
physical diameters of the Sun and the Moon?
23
Solution First step outline the problem in a
diagram. r 1.496?108 km (Sun), r
3.844?105 km (Moon) Since the angles in both
cases are small, roughly 0.5, it is possible to
solve for the angular diameter using the small
angle equation, namely where the angle ? is
expressed in dimensionless units, radians. 1
radian 206265 arcseconds
24
For the Sun, r 1.496?108 km and ?
1920". For the Moon, r 3.844?105 km and
? 1865". Actual mean diameter of Moon
3475 km.
25
2. The Hubble image below shows the satellites
Titan (upper right), Enceladus, Dione, and Mimas
(lower left) in transit across the planet Saturn.
The equatorial diameter of Saturn is 120,536 km.
What is the diameter of Titan? Solution
Measured diameters of the two images are 2¼ mm
and 53 mm, respectively. The agreement is
exact to within the 2 significant figure accuracy
of the measurements.
26
The Summer Triangle Groups that look like their
namesakes.
27
Hercules Normally pictured holding the world.
28
Sagittarius An archer? Better pictured as a
teapot.
29
The Perseus Group A story in the stars.
30
Ursa Major Does this group truly look like a
bear??!
31
Finding Polaris
32
A better way? - from Rambling Through the Skies,
George Lovi, Sky Telescope, December 1990.
33
The stars of Orion as pointers.
34
The field of Orion
35
The Heavenly G. Captain, all duh riggin seems
perfectly polished.
36
Stars are presently designated in a variety of
ways Greek letters, from east to west for stars
of comparable brightness (UMa)
37
Greek letters, from from brightest to faintest
for stars of comparable brightness (Ori, Cas), as
well as Bayer-Flamsteed numbers
38
Archaeoastronomy. Many constellations bear names
originating from eras when the stellar
configuration bore some resemblance to the object
after which they are named, e.g. Ursa Major, the
Great Bear.
39
Some were named for other reasons, e.g. Hydra.
40
Stars on the celestial equator (CE) rise due east
and set due west. In 2600 BC Hydra lay along the
CE, making then useful for navigation at night.
41
Only 50 of the 88 modern constellations were
known in antiquity. They also outlined
only regions in the northern sky, most being
named by ancient Minoans.
42
Ancient star maps.
43
Zodiacal Constellations, Astrological Eras, and
the link to precession.
44
The Taurus and Aries Eras.
45
The Beginnings? The Gemini Era.
46
The present.
47
The old constellation of Argo, the Ship, was very
large. It was but one of many symbols associated
with the story of Noahs Ark.