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Physics > Universe > Flashcards

Universe Flashcards

1
Q

Number of natural satellites in our solar system

A

59

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2
Q

Planets that don’t have any natural satellite

A

Mercury

Venus

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3
Q

Planet having maximum satellites and number of satellites it has

A

Saturn

Has 21 satellites

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4
Q

Ways in which stars can occur

A

Single stars
Binary stars
Clusters

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5
Q

Type of galaxies

A

Spiral
Elliptical
Irregular

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6
Q

Mass of Milky Way galaxy

A

M = (v^2 x r) / G
= 3 x 10^41 kg
=150 billion solar masses

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7
Q

What are asteroids

A

It is believed that asteroids are pieces of planets possibly due to gravitational effect of Jupiter

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8
Q

Comets?

A

Are small rock like material surrounded by large masses like water, ammonia and methane revolving in highly elliptical orbits around the sun

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9
Q

Meteors and meteorites?

A

Objects that get completely burned and blazing through the atmosphere are called meteors

While objects that aren’t completely burned are called meteorites

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10
Q

Hottest star

A

Blue star

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11
Q

Coolest star

A

Red Star

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12
Q

Observations in favour of Big Bang theory

A

Expanding universe

Red shift

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13
Q

Pulsating theory

A

States that the boundary of universe moves in and out with a time period of 8 x 10^9 years

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14
Q

Steady state theory

A

States that total number of galaxies present in the universe has attained a steady value.
Thus if one galaxy is lost another is lost due to annihilationa new ones formed

This theory is based on conservation of energy and mass

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15
Q

Hubble’s law

A

States that speed of recession(v) is related to distance(r) of Galaxy by the relation

v=Hr

H-Hubble’s constant = 10^17 kms-1/million light years

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16
Q

Formation of stars

A

Dust particles, Hydrogen and helium gas molecules in interstellar space combine together at -173 C
to form a cloud.

Try then start to contract and as a result of compression heating of cloud takes place.

At about 10^7 K fusion of H atoms is initiated with release of energy which keeps the stars shining for millions of years.

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17
Q

Death of star

A

After H in the core is exhausted the core starts contracting which increases the temperature

As a result the outer layer starts contracting which brings about a cooling effect

This process continues till the outer layer’s temperature drops to a point where the star appears red and the star is then called a Red Giant

This is followed by a violent explosion called nova/supernova in the star which throws the outer layers into interstellar space.

The left core may then convert into any one of the following before ultimately dying

1] white dwarf
2] Neutron star
3]Black Hole

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18
Q

White dwarf?

A

Was discovered by S. Chandrasekhar

The core which is made of protons and electrons dies as white dwarf of star’s original mass was 1.4 solar masses. This called Chandrasekhar limit.

Stars colour changes from white to yellow to red and finally black.

It then becomes invisible.

19
Q

Neutron star

A

The core made up of neutrons finishes up as neutron star if it’s original mass is between 1.5 to 5 solar masses

These stars produce very high magnetic fields

20
Q

What’s a Pulsar

A

A spinning neutron star emitting electromagnetic waves is called Pulsar

21
Q

Black Hole

A

If the original mass of star is greater than 5 solar masses it dies as a black hole

22
Q

Why does black hole have large gravitational pull?

A

Because mass of black hole is greater than that of sun but it has a small size and hence large gravitational pull

23
Q

Composition of Milky Way

A

It is composed of a few hundred billion stars i.e. 150 billion stars

24
Q

When and by whom was the Milky Way discovered

A

In 18th century by William Herschel

25
Q

Uranus was discovered by

A

William Herschel

26
Q

What’s interstellar matter

A

It is the space in the Milky Way that is filled with dust particles and gases

27
Q

Interstellar matter consists

A

90% hydrogen

28
Q

Dark nebulae

A

Are regions which appear dark because the intervening dust and gas obstruct the light from the stars behind

29
Q

Bright nebulae

A

These are regions showing great variety of brightness as they shine in the light of the nearby stars

30
Q

Example of a bright nebulae

A

Orion

31
Q

Milky Way’s rotation is

A

Not rigid

32
Q

Planetary systems revolve around a the centre of Milky Way with a speed of

A

250km/s

33
Q

Time taken by sum to complete one revolution

A

250 million years

34
Q

Percentage by mass of interstellar matter present in Milky Way

A

1.5%

35
Q

Why does tail of a comet point away from sun?

A

Due to radiation pressure only

36
Q

Spectrum of a star

A

Line absorption spectrum (usually)

37
Q

Main characteristics of black hole

A

It absorbs photon

38
Q

Spectrum of stars is closely related to

A

Colour

39
Q

White dwarfs are

A

Very small stars having diameter 1/5th of sun

40
Q

Dwarfs?

A

These are most common stars like sun

41
Q

1 Astronomical Unit (AU) is equal to

A

1.496 x 10^11 m

42
Q

alpha = ?

A

Diameter / Distance

43
Q

Reflecting power of planets is called

A

Albedo

44
Q

Gravitational energy of sun =

A

-(3/5) x (GM^2)/R

Physics (49 decks)

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