The Solar System

388.9 nm

1875.1 nm

1281.8 nm

1093.8 nm

1005.0 nm 954.6 nm

...

..

.

..

.

397.0 nm

410.2 nm

434.0 nm

486.1 nm

656.3 nm

93.8 nm
95.0 nm
97.2 nm
102.6 nm
121.5 nm

...
...

H

H

H

Balmer series

(Visible-UV)

Paschen series

(IR)

Lyman

series

(UV)

Nucleus

500

Wavelength (nm)

Visual-wavelength imageVisual-wavelength image

600 700

Intensity

H

H H

Balmer lines

Paschen lines

Lyman lines

100 nm

500 nm

1000 nm

1500 nm

Infrared

Visible

Ultraviolet

2000 nm

H

H

H

..

.

The shorter-wavelength

lines in each series

blend together.

2

3

The electron orbits in the hydrogen atom are

shown here as energy levels. When an electron

makes a transition from one orbit to another, it

changes the energy stored in the atom. In this

diagram, arrows pointed inward represent transitions

that result in the emission of a photon. If the arrows

pointed outward, they would represent transitions

that result from the absorption of a photon. Long

arrows represent large amounts of energy and

correspondingly short-wavelength photons.

Modern astronomers rarely
work with spectra as bands of
light. Spectra are usually recorded
digitally, so it is easy to represent
them as graphs of intensity versus
wavelength. Here the artwork
above the graph suggests the
appearance of a stellar spectrum.
The graph below reveals details not
otherwise visible and allows
comparison of relative intensities.
Notice that dark absorption lines in
the spectrum appear as dips in the
curve of intensity.

2a Transitions in the hydrogen atom can be grouped into series—the Lyman series,

Balmer series, Paschen series, and the like.

Transitions and the resulting spectral lines are

identified by Greek letters. Only the first few

transitions in the first three series are shown

at left.

2b In this drawing (right) of the hydrogen spectrum,

emission lines in the infrared and

ultraviolet are shown as gray. Only

the first three lines of the Balmer

series are visible to human eyes.

2c Excited clouds of gas in space emit light at all of the

Balmer wavelengths, but you see

only the red, blue, and violet

photons blending to create the

pink color typical of ionized

hydrogen.

AURA/NOAO/NSF