Download Eclipses

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What is an eclipse?
• A solar eclipse occurs when the Moon
comes between the Sun and the
observer.
• A lunar eclipse occurs when Earth
comes between the Sun and the Moon.
• A total eclipse happens when the
moon entirely blocks the Sun or the
Earth's shadow totally blocks our view
of the moon
• An annular eclipse occurs when the
Sun and Moon are exactly in line, but
the apparent size of the Moon is
smaller than that of the Sun.
•A hybrid eclipse is intermediate
between a total and annular eclipse. At
some points on the surface of the Earth
it is visible as a total eclipse, whereas at
others it is annular.
Phases of the Moon
• Eclipses will occur during some of these phases.
• There are many kinds of eclipse, two of which
are solar and lunar eclipses.
Solar Eclipses
Solar Eclipses
• Occur at New Moon because we will not be
able to see the moon due to the illuminated
side of the moon being pointed away from
Earth.
• If the moon’s shadow happens to fall upon
Earth’s surface at that time, we will see some
portion of the sun’s disk covered or ‘eclipsed’
by the moon.
Lunar Eclipses
• Earth’s shadow is composed of two cone – shaped
components, one inside the other.
Lunar eclipses
• Everyone on the night side of Earth can see an
eclipse of the Moon when it takes place
• Lunar eclipses can be useful because you can
measure the exact time when each crater of
the moon enters and leaves the umbral
shadow.
• These crater timings can be used to estimate
the enlargement of the earth’s atmosphere
due to airborne dust and volcanic ash.
Why don’t they occur every month when the
moon is in the full moon phase?
• The Moon’s orbit about Earth is tilted 5 degrees to
Earth’s orbit around the sun.
• Meaning the moon spends most of the time either
above or below the plane of earth’s orbit.
• The plane of Earth’s orbit around the Sun is
important because Earth’s shadows lie in exactly the
same place.
• During Full Moon, the Moon usually passes above
or below earth’s shadows and misses them entirely
so no eclipse takes place.
Partial and Total Lunar Eclipses
• From 2000BC through 3000 AD, there are
7,718 eclipses of the Moon
• There are anywhere from 0 to 3 lunar eclipses
each year.
• The last time that three total lunar eclipses
occurred in one calendar year was in 1982.
• Partial eclipses slightly outnumber total
eclipses by 7 to 6.
Partial and Total Solar Eclipses
Year
Total
Partial
Annular
Hybrid
1998
1 (Feb)
0
1 (Aug)
0
1999
1 (Aug)
0
1 (Feb)
0
2000
0
5 (Feb, July
(x2), Dec)
0
0
2001
1 (June)
0
1 (Dec)
0
2002
1 (Nov)
0
1 (June)
0
2003
1 (Dec)
0
1 (May)
0
2004
0
2 (Apr,
Oct)
0
0
2005
0
0
1 (Apr)
1 (Apr)
2006
1 (Mar)
0
1 (Sept)
0
2007
0
2 (Mar,
Sept)
0
0
2008
0
0
1 (Feb)
0
2009
2 (July &
Aug)
0
1 (Jan)
0
Total Eclipse in Cornwall 11/08/1999
•The last total eclipse in Britain prior to this, was over 80 years ago, for us in Britain this
is a once in a lifetime experience.
•The partial eclipse started at about 10 a.m., and by 11.11 it was total darkness, and
returns to partial eclipse approximately 2 minutes later, before full sunlight is restored
around noon
Binary Stars
• A binary star system consists of 2 stars that orbit around
a common point
• Four types of binary system
–
–
–
–
Visual binaries
Spectroscopic binaries
Eclipsing binaries
X-ray binaries
• 5-10% of visible stars are visual binaries
• ~50% of all stars are members of binary systems
Background image: Artists impression of
binary system called HD 113766
Visual and Spectroscopic Binaries
• Visual binaries:
– Individual stars visible through a telescope
• Spectroscopic binaries:
– Stars are so close together they appear as a single star
– Binary nature deduced from their periodic Doppler
shifts of wavelengths of lines seen in spectrum
– Double-lined spectroscopic binaries – spectrum shows
lines from both stars
– Single-lined spectroscopic binaries – only one set of
lines seen, other is too faint
Eclipsing and X-ray Binaries
• Eclipsing binaries:
– Orbital plane is oriented exactly edgewise to the plane of
the sky so one star passes directly in front of the other,
blocking out its line during the eclipse
– May also be visual or spectroscopic binaries
• X-ray binaries:
– Emit x-rays
– Made up of normal star and collapsed star
– These pairs of stars produce X-rays if the stars are close
enough together that material is pulled off the normal
star by the gravity of the dense, collapsed star.
Transits
• Occurs when, for example, a planet passes across the
disk of the Sun.
• On Earth we only experience transits of Mercury and
Venus.
• Transits far rarer than eclipses of the Sun by the
moon.
• On average we experience 13 transits of Mercury
each century.
• Transits of Venus are much rarer
• The first transit that was recorded was in 1631 by the
French astronomer Gassendi.
Transits of Mercury
• Transits of Mercury occur within a few days of
either 8th May or 10th November.
• Transits will occur if Mercury passes into the
path between the Earth and the Sun at this
time.
• Chances of a November transit occurring are
almost twice as high as those for a May transit
• The last transit of Mercury occurred on 7th
May 2003, being the first one seen since 1999.
Visibility of 7th May 2003 Transit of
Mercury
Transits of Venus
• Only 6 transits of Venus since the invention of the
telescope, occurring in 1631, 1639, 1761, 1769,
1874 and 1882.
• Transits of Venus only occur in early December
and June.
• The last transit of Venus occurred on 8th June 2004
• The next will occur on 6th June 2012
Visibility of 8th June 2004 Transit of Venus